https://en.wikipedia.org/wiki/Animal_locomotion
Animals move in a variety of ways to get from A to B. Common modes of locomotion are initiated by self-propulsion e.g. running, swimming, jumping, flying, hopping, soaring and gliding. Many other animal species choose the most suitable transportation method based on the environment, known as “passive locomotion”. e.g. Sailing (jellyfish), Kiting (spiders), Rolling (beetles and spiders), riding other animals (Phoresis). We have known animals move because they are either searching for food, a suitable mate, an appropriate microhabitat, or escaping predators. The ability to move helped many animals survive, which resulted in natural selection shaping the most effective locomotion methods and mechanisms for mobile organisms. For instance, non-migratory animals must have energetically costly but rapid locomotion in order to frequently move quickly to escape predators. Meanwhile, migratory animals such as the Arctic tern have energetically economical locomotion mechanisms in order to travel vast distances. Common locomotory organs or anatomical structures include cilia, legs, wings, arms, fins, or tails.
Animals move through, or on, 4 types of environment:
(a) Aquatic = In or on water
https://en.wikipedia.org/wiki/Aquatic_locomotion
https://en.wikipedia.org/wiki/Fish_locomotion
Aquatic locomotion is a biologically propelled motion through a liquid medium. The mechanics of swimming evolved many times in a range of organisms ranging from arthropods, fish, molluscs, reptiles, birds and mammals.
The first 3 swimming animals may have appeared in the Early to Middle Cambrian, even though jellyfish fossils were discovered in the Ediacaran. They were closely related to the arthropods, including the Anomalocaridids, which swam in a similar manner to cuttlefish by means of lateral lobes. In Early Cambria, chordates were hypothesised to be swimming before cephalopods joined the ranks of the nekton in late Cambria. Although many terrestrial animals retained a certain capacity to swim, some organisms, nevertheless, returned to the water and developed the capacities for aquatic locomotion. Most apes (including humans) didn’t, hence lost the instinct to swim. In 2013, Pedro Renato Bender proposed that “Saci last common ancestor hypothesis” (named after Saci, a Brazilian folklore character who cannot cross water barriers). He thought the loss of instinctive swimming ability in apes were due to constraints related to the adaptation to an arboreal life in the last common ancestor of apes. He hypothesised the increased risks of exposure to water than the advantages of crossing water increasingly contributed to ancestral apes’ avoidance of deep-water bodies. This decreased contact with water bodies may have led to the disappearance of the doggy paddle instinct.
How do micro-organisms swim?
For example, the centre of mammalian spermatozoon contains mitochondria that help energise movement of the sperm’s flagellum. The motor around the base produces torque, just like in bacteria for movement through the aqueous environment.
How do invertebrates swim?
Among the radiata, jellyfish and their kin, invertebrates mainly swim through flexion of their cup-shaped bodies. All jellyfish are free-swimmers, albeit passively. Passive swimming is akin to gliding, which involves floating along fluid currents in order to conserve energy when controlling its position or motion. On the other hand, active swimming requires energy expenditure to move in the desired direction.
In bilateria, arrow worms (chaetognatha) undulate their finned bodies, while nematodes undulate their fin-less bodies. Some arthropod groups including crustaceans, such as shrimp, usually swim by paddling with their special swimming legs called “pleopods”. Crabs use their modified walking legs called “pereiopods” to swim, whereas Daphnia beat its antennae to swim.
Molluscs like free-swimming sea slugs and sea angels have flap fin-like structures to help them swim. Some shelled molluscs such as scallops and cephalopods clap their 2 shells together by opening and closing them in order for them to swim.
Deuterostomia such as feather stars and vertebrates (notably fish) swim by undulating their numerous arms. Salps pump water through their gelatinous bodies to move through fluid medium.
https://www.youtube.com/watch?v=9OIjaHIrM0U
i. Jet Propulsion
This method of aquatic locomotion involves animals filling a muscular cavity with water and squirting it out to propel them in the opposite direction of the squirting water. For instance, jellyfish draw water from its rear and then expel it from the same end. Through this method of propulsion, the aquatic animals’ velocity fluctuates during movement due to the expanse of the contracting cavity. Nevertheless, expulsion of water through its rear leads to acceleration while vacuuming of water leads to deceleration. Assuming fluctuations in drag and mass are negligible, a high-enough frequency of jet-propulsion cycles may make this method a relatively inefficient method of aquatic locomotion.
Animals known to move via jet propulsion are cephalopods, jellyfish, scallops and starfish.
— Cephalopods require high amounts of energy expenditure to move by jet propulsion, which decreases its relative efficiency as the size of organism increases. Since the Paleozoic, the environment gradually suited the more efficient motion of fish than cephalopods in order to increase its chances of survival, as fins and tentacles were able to maintain a steady velocity unlike jet propulsion. However, the stop-start motion of jet propulsion is useful for escaping predators or capturing prey as it requires explosive bursts of extreme speed. This means cephalopods are the fastest marine invertebrates, accelerating quicker than most fish. Cephalods first absorb oxygenated water into their mantle cavity to its gills. Second, muscular contraction of this cavity expels the spent water through the hyponome, created by a fold in the mantle. Since they expel water anteriorly through the hyponome, cephalopods usually move backwards but their desired direction is controlled by pointing the spent water in different directions. Cephalopods that are neutrally buoyant need not swim to remain afloat. Although squid swim slower than fish, they use more power to accelerate to a rapid velocity. The limit in the amount of water accelerated out of the squid’s mantle cavity contributes to the inefficiency of jet propulsion.
— Jellyfish have a 1-way water cavity to generate each phase of continuous cycles of jet-propulsion followed by a rest phase. The Froude efficiency of method is about 0.09, which is interpreted as a costly method of locomotion. Compared to fish of equal mass, the metabolic expenditure of transport for jellyfish is high.
— Scallops adopt a similar jet propulsion design to jellyfish by swiftly opening and closing their shells, then drawing in water and expelling it from all sides. This helps them escape predators such as starfish. In addition, its shell acts as a hydrofoil to counteract the scallop's tendency to sink. The Froude efficiency for this locomotion is about 0.3, which makes it preferable for emergency situations to escape from predators. Nonetheless, the elastic hinge connecting both of the scallop’s shells mitigates the work required to carry out its locomotion.
— Elastic energy becomes stored in abductin tissue of scallop muscles when shell is closing, which acts like a spring to open the shell. This elasticity reduces the work done against the water as the openings is quite large when water enters and quite small when water leaves. Furthermore, the work of inertia of scallop jet-propulsion is quite low too. This makes the minimal energy savings created by the abductin tissue negligible.
Medusae can also use their elastic mesoglea to enlarge their bell.
How do fish swim?
https://en.wikipedia.org/wiki/Fish_locomotion
Fish swim by exerting force against the surrounding water. Fish typically contract their muscles on either side of its body in order to generate waves of flexion that travel the length of the body from nose to tail, generally expanding as they go along. The vector forces exerted on the water by such motion cancel out laterally, and generate a backwards net force that pushes the fish forward through the water. While most fishes generate thrust using lateral movements of their body and caudal fin, many other species move mainly using their median and paired fins. However, the latter group swim slower than the former group, but can turn rapidly, which is important when living in coral reefs for instance.
A. There are 5 groups of body / caudal fin propulsion that differ in terms of the fraction of their body being displaced laterally.
(i) Anguilliform = This group contains some long, slender fish such as eels. They show little increase in the amplitude of the flexion wave as it passes along the body. e.g. Eels propagate a more or less constant-sized flexion wave along their slender bodies.
(ii) Sub-carangiform = This group shows a more marked increase in wave amplitude along the body with most work being done by the rear half of the fish. Their bodies are stiffer, allowing it to move at higher speeds at the expense of manoeuvrability. e.g. Trout
(iii) Carangiform = Named for the Carangidae, this group is stiffer and faster-moving than the previous groups. Most of their locomotion is concentrated in the rear end of the body and tail, meaning they rapidly oscillate their tails.
(iv) Thunniform = This group contains high-speed long-distance swimmers, such as tunas and several lamnid sharks. Their tails and the region connecting the main body to the tail (the peduncle) move virtually sideways. This enables these fish to chase and catch prey easier due to the increase in speed of swimming, like in Barracudas.
Tunas such as the bluefin swim fast with their large crescent-shaped tails.
(v) Ostraciiform = This group doesn’t have any appreciable body wave when they employ caudal locomotion. They generate thrust by rapidly oscillating only their tail fin. e.g. Ostraciidae.
B. Median / Paired Fin Propulsion
Many fish swim by combining the behaviour of their 2 pectoral fins or both their anal and dorsal fins. Different types of median / paired fin propulsion can be achieved by preferentially using 1 fin pair over the other.
e.g. Ocean sunfish have a tetraodontiform mode system, while many other fish use their pectoral fins to swim, steer and perform dynamic lift. Fish with electric organs, such as those in the knifefish (Gymnotiformes), swim by undulating their long fins while stabilising its body in order to disturb the electric field being generated.
(i) Rajiform = This locomotion is seen in rays, skates, and mantas where their large, well developed pectoral fins vertically undulate to produce thrust.
(ii) Diodontiform = This locomotion is seen in fish, such as porcupinefish (Diodontidae), where their large pectoral fins propagate undulations to propel them.
(iii) Amiiform = This locomotion is seen in the bowfin, where their long dorsal fin undulate while their body axis is stabilised and straightened.
(iv) Gymnotiform = This locomotion is seen in the knifefish (Gymnotiforms), where their long anal fin undulates. It essentially is an inverted amiiform.
(v) Ballistiform = This locomotion is seen in the family Balistidae (triggerfishes) and Zeidae, where both anal and dorsal fins undulate.
(vi) Oscillatory = This locomotion is also known as ‘mobuliform locomotion’ or pectoral-fin-based swimming. It is seen in Pelagic stingrays, such as the manta, cownose, eagle and bat rays, where motion is produced by less than half a wave on the fin, similar to a bird wing flapping.
(vii) Tetrodontiform = This locomotion is seen in the Tetradontiformes (boxfishes and pufferfishes) e.g. ocean sunfish, where their dorsal and anal fins flap as a unit, either in phase or exactly opposing one another.
(viii) Labriform = This locomotion is seen in the wrasses (Labriformes), where their pectoral fins oscillate based on drag or lift. They generate propulsion either by dragging the fins through the water in a rowing motion in response to drag, or via lift mechanisms.
Describe the dynamics of swimming
Since fish have quite dense bone and muscle tissue, their gas bladders helps increase its buoyancy in order to maintain depth. Other fish store oils or lipids to achieve the same aim. If fish lack these features, they instead use dynamic lift by flapping their pectoral fins. During their swimming motion, fish position their pectoral fins to generate lift, which allows them to maintain a certain depth. The drawbacks of this method include the requirement of constant motion to maintain buoyancy and the inability to swim backwards or hover.
Swimming animals produce thrust to overcome the water’s drag to exert powered swimming, similar to the aerodynamics of flight. Unlike flying, however, they need not supply much vertical force because the upwards buoyancy force counters the downwards gravitational force, which allows them to float effortlessly. Swimming behaviour is classified into 2 distinct “modes” according to the body structures involved in thrust production: Median-Paired Fin (MPF) and Body-Caudal Fin (BCF). Each classification has numerous specifications along a spectrum of behaviours from purely undulatory to entirely oscillatory. Undulatory swimming modes involves wave-like movements of the propulsive structure e.g. fin or the whole body to generate thrust, while oscillatory modes involves swivel movements of propulsive structure on an attachment point without any wave-like motion to generate thrust.
Most fish generate undulatory waves that propagate down the body through the caudal fin to generate swimming propulsion, which is known as Body-Caudal Fin (BCF) swimming. This includes anguilliform, sub-carangiform, carangiform, and thunniform locomotory modes, and the oscillatory ostraciiform mode.
Swimming fish adapt behaviours in order to achieve a balance of stability and manoeuvrability. BCF swimming is effective in quick acceleration and continuous cruise motion as it relies on more caudal body structures to direct powerful thrust rearwards. Therefore, it is inherently stable and often observed in fish with large migration patterns that maximise efficiency over long periods. On the other hand, the coordination of movement of multiple bilateral fins generate propulsive forces in MPF swimming helps execute elaborate turns. This helps MPF swimming adapt to movements requiring high manoeuvrability, hence it’s often observed in smaller fish requiring elaborate escape patterns. A 2005 study found a relationship between the habitats occupied by fishes and their swimming capabilities. For instance, on coral reefs, faster-swimming fish species typically live in wave-swept habitats subject to fast water flow speeds, while the slower fishes live in sheltered habitats with low levels of water movement.
A 1999 study argued that fish don’t exclusively on 1 locomotor mode, but are rather locomotor generalists, meaning they choose among and combine behaviours from many available behavioural techniques. A 2013 study found the BCF swimmers predominantly incorporate movement of their pectoral, anal, and dorsal fins as an additional stabilising mechanism at slower speeds. A 1999 study found they hold those aforementioned fins close to their body at high speeds to improve streamlining and reduce drag. A 2006 study found zebrafish altered their locomotor behaviour in response to changing hydrodynamic influences throughout growth and maturation.
Due to the variety of depth of aquatic ecosystems, controlling buoyancy effects is critical for aquatic survival. In order to control their depth, fish generally regulate the amount of gas within their specialised organs. They can actively control their density as they change the amount of gas in their swim bladders. When the amount of air in their swim bladder increases, this lowers their overall density below the surrounding water. Hence, this increases upward buoyancy pressures, which causes the fish to rise until they reach a depth of equilibrium with the surrounding water.
What are hydrofoils?
Fish with Hydrofoils or fins use them to push against the water generating a normal force to provide thrust, propelling it through water. For instance, sea turtles and penguins beat their paired hydrofoils to create lift. Leopard sharks have a pair of pectoral fins that are angled at varying degrees to allow the animal to rise, fall, or maintain its level in the water column. Reducing the fin surface area minimises drag, thus increases efficiency. Regardless of size, at any speed, maximum possible lift is proportional to (wing area) x (speed)2 . Many fish and sharks have vertical caudal hydrofoils, while dolphins and whales have large, horizontal caudal hydrofoils. Cetaceans, penguins, and pinnipeds porpoise in order to conserve energy when moving at high speeds. Since drag increases with speed, the work required to swim unit distance is greater at higher speeds, but the work needed to jump unit distance is independent of speed. Therefore, seals use their caudal tail to propel themselves through the water, while sea lions use their pectoral flippers to create thrust solely.
What is drag powered swimming?
When an organism collide with the fluid’s molecules, it creates friction. This causes drag against moving fish, which explains the emergence of many fishes’ streamlined shape. A streamlined shape works to reduce drag through orientation of elongated objects parallel to the direction of drag force, therefore it allows water currents to pass over and taper off the end of the fish. This leads to efficient energy use in aquatic locomotion. Some flat-shaped fish have a flat bottom surface and curved top surface to take advantage of pressure drug, which generates upward lift.
Aquatic organisms with appendages use them for propulsion in 2 main and biomechanically extreme mechanisms. Some use them for lift-powered swimming, analogous to flying animals as appendages flap like bird wings, and decrease drag on the appendage’s surface.
How do fish larvae swim?
https://www.youtube.com/watch?v=wtIhVwPruwY
The larvae of any ray finned fish, such as the Actinopterygii, swim at between 10 and 900 Reynolds Number. This places them in an intermediate flow regime where both inertial and viscous forces play an important role. As larvae size increases, the use of pressure forces to swim at higher Reynolds number increases.
At least 2 types of wake are shed by undulatory swimmers: Connected vortex loops are shed by carangiform swimmers, whereas individual vortex rings are shed by Anguilliform swimmers. The shape and arrangement of the trailing edge from which the vortices are shed influence the structure of the vortex rings. A 2008 study evaluated swimming speed, and ratio of swimming speed to body wave speed and the shape of body wave influence the pattern of the vortex rings.
There are 3 phases to spontaneous bouts of swimming. (1) The start or acceleration phase involves the larva rotating its body to make a 'C' shape, known as the ‘preparatory stroke’. Then it pushes in the opposite direction to straighten its body, known as a ‘propulsive stroke’ (or a ‘power stroke’) propelling the larva forwards. (2) Cyclic swimming involves the larva swimming at a relatively constant speed. (3) The deceleration phase involves the larva gradually slowing down to a complete stop. Due to its body bending, the larva’s preparatory stroke involves the creation of 4 vortices around its body, 2 of those are shed in the propulsive stroke. In the vortices of the deceleration phase, a large area of elevated vorticity can be seen compared to the starting phase.
The swimming abilities of larval fish play an important survival role. This means larval fishes with higher metabolic rate and smaller size are more susceptible to predators. This helps reef fish larva settle at a suitable reef and locate its home, which is often isolated from its home reef in search of food. They are found to swim between ~12 cm/s - 100 cm/s, which is quite fast compared to other larvae. Despite the swimming speeds of larvae fish from the same families, their variations create a wide spectrum. At a species level, their body length is significantly related to their swimming ability. At the family level, only 16% of variation in swimming ability can be explained by length according to a 2005 study. A negative correlation is evaluated between the fineness ratio and the swimming ability of reef fish larvae, which suggests a minimisation of overall drag and maximisation of volume. In a 2004 study, reef fish larva among taxa differ significantly in their critical swimming speed abilities, leading to high variability in sustainable swimming speed. Hence, this causes sustainable variability in their ability to alter dispersal patterns, overall dispersal distances and control their temporal and spatial patterns of settlement.
Examples of larval fish:
— Atlantic herring eggs
— Late-stage lanternfish larva
— Late-stage scaldfish larva (9mm)
— Larva of conger eel (7.6cm)
— Bluefin tuna larva
— Pacific cod larva
— Walleye larva
— Common sturgeon larva
— Boxfish larva
— Ocean sunfish larve (2.7mm)
Hydrodynamics:
Both inertial and viscous forces enact on small undulatory swimmers, which indicates the relative importance of Reynolds number (Re). Since Re is proportional to body size and swimming speed, the swimming performance of a larva increases between 2–5 days post fertilisation (d.p.f.). Compared with adults, the larval fish experience relatively high viscous force. In order to increase thrust to that of adult fish, larval fish increase their tail beat frequency and thus amplitude. As they age, larval fish increase their tail beat frequency to 95 Hz in 3 dpf from 80 Hz in 2 dpf. This increases their swimming speed, hence reduces their predation and increases their prey catching ability upon their first feed around 5 dpf. The flow regime inversely and non-linearly influences the vortex shedding mechanics of larval fish. A 2015 study considered Reynolds number (St) as a design parameter for vortex shedding mechanism that defines the ratio of product of tail beat frequency with amplitude with the mean swimming speed. Studies argue Re is the main deciding criteria of a flow regime, since slow larvae swim at higher St but lower Re and vice versa for faster larvae. Since St is directly proportional to the small size of swimmers and flow regime, this gives similar speed ranged adult fishes a constant St. In general, fishes swimming in viscous or high-friction flow regimes create more body drag, which lead to higher St. Conversely, adult fish swimming viscous or high-friction flow regimes have lower stride lengths, leading to shorter tail beat frequency and smaller amplitude. For the same displacement or higher propulsive force, this increases thrust, hence unanimously reduces Re.
At 5-7 dpf, larval fishes begin feeding, by which they experience extreme mortality rate (~99%) few days afterwards, known as the ‘Critical Period’. This Critical Period is mainly due to hydrodynamic constraints. Even if there are adequate prey encounters, larval fish still fail to eat. Therefore this makes the size of larval body one of the primary determinants of feeding success. This makes smaller larvae function in a lower Re regime. The size of larvae increases with age, which increases both their swimming speed and Re. Experiments conducted within the last 5 years found Re~200 (Reynolds number of successful strikes) is higher than the Re~20 (Reynolds number of failed strikes). A 1988 study concluded around 40% energy invested in mouth opening is lost to frictional forces rather than contributing to accelerating the fluid towards mouth according to their Numerical analysis of suction feeding at a low Re. A 2017 study determined the relationship between larvae’s feeding success and ontogenetic improvement in the sensory system, coordination and experiences as non-significant. Successful strikes correlates positive with the peak flow speed or the speed of larvae at the time of strike. Moreover peak flow speed correlates with gape speed or the speed of opening the buccal cavity to capture food. China et al. found larva cumulatively increase the successful strike outcomes with age, body size and gape speed. Therefore, larger larvae develop capabilities in capturing faster escaping prey and exerting sufficient force to suck heavier prey into their mouths.
A larval prey’s ability to sense and evade the strike determines their survival rate when encountering a predator. Adult fishes typically exhibit rapid suction feeding strikes, compared to larval fishes. Larvae’s critical defence against predation depends on their sensitivity of larval fish to velocity and flow fields. In the daytime, many prey utilise their visual system to detect and evade predators. In the dark, however, there are visual difficulties detecting predators, leading to the prey’s delayed responses to predatory attacks. Nevertheless, a 2013 study found fishes have a mechano-sensory system to allow them to detect differences in flow generated by different motions surrounding the water and between the bodies, known as a ‘lateral line system’. When their lateral line system detects a predator, the larva evades its strike by 'fast start' or 'C' response. Other aquatic prey such as copepods and crustaceans have setae to sense water flow along their antennas, which is not too dissimilar to the lateral line system. When a swimming fish disturbs a volume of water ahead of its body with a flow velocity, this increases the flow’s proximity from its body. Ferry, Wainwright and Lauder describe this phenomena as a ‘Bow Wave’. This means the escape probability is inversely dependent on the timing of the 'C' start response. Therefore, at the time of strike, escape probability increases with the distance from the predator. A 2013 study concluded that prey successfully evade a predator strike from an intermediate distance (3–6 mm) from the predator. Prior to suction feeding, prey could react by detecting the flow generation of an approaching predator by startle response. Well-timed escape maneuvers are crucial for a larval fish’s survival.
Behaviour:
The complex and diverse locomotor repertoire and neural systems of higher vertebrates complicates objective quantification.
How do amphibians swim?
Most of the amphibia have a larval state, which has inherited anguilliform motion from fish ancestors, and an accompanying laterally compressed tail. Corresponding tetrapod adults forms (e.g. sub-class Urodeles that retained its tail) are occasionally aquatic to a negligible extent. However the majority of Urodeles, from the newts to the giant salamander Megalobatrachus, retain a laterally compressed tail useful for carangiform motion. One exception is the genus Salamandra, whose tail has lost its suitability for aquatic propulsion.
A majority of the tailless amphibians (e.g. frogs and toads of the sub-class Anura) are aquatic to an insignificant extent in adult life. However, A considerable aquatic minority adapted the tailless-tetrapod structure for aquatic propulsion, which is a problem. Their locomotion mode is unrelated to those used by fish. Their flexible back legs and webbed feet allow them to execute leg movements similar to a human ‘breast stroke’, rather more efficiently because their legs are more streamlined.
How do reptiles swim?
Modern members of the class Reptilia descended from the archaic tailed Amphilia, making it an obvious case in the order Crocodilia (crocodiles & alligators), in regards to aquatic propulsion. They use their deep, laterally compressed tails in an essentially carangiform mode of propulsion. Despite their hydromechanical shape featuring roughly circular cross-section and gradual posterior taper, terrestrial snakes swim fairly readily by required, using anguilliform propulsion. Usually tetrapods experience difficulty swimming but Cheloniidae (true turtles) evolved their forelimbs into flippers of high-aspect-ratio wing shape to imitate a bird's propulsive mode more accurately than do the eagle-rays themselves.
How does fin and flipper locomotion work?
https://en.wikipedia.org/wiki/Fin_and_flipper_locomotion
Swimming mammals, such as whales, dolphins, and sea lions, use their flippers to move forward through the water column. When sea lions swim, they have a thrust phase followed by a recovery phase, which lasts about 60% and 40% of the motion cycle respectively. In 1985, Godfrey recorded a full cycle duration lasting about 0.5 - 1 sec. Rapid manoeuvres such as changing direction requires initiation of head movement toward the animal’s back followed by their body performing a spiral turn. Because their pectoral flippers are closely located to their centre of gravity, sea lions demonstrate capability in manoeuvrability in the pitch, roll, and yaw direction. Thus sea lions are not constrained, turning stochastically as they please. Researchers hypothesise the complex habitat contributes to the increased level of manoeuvrability of marine animals. Difficult environments featuring rocky inshore / kelp forest communities provide prey many niches to hide, therefore predators hunting in their environments require speed and manoeuvrability to capture prey. A 2004 study discovered sea lions learn complex skills early on in ontogeny and perfect them as pups by 1 year of age. Although whales and dolphins have less manoeuvrability, meaning their movements are more constraints, thus limited in rapid and efficiently turning, they have, however, faster accelerations than sea lions. The centre of gravity in both whales and dolphins does not align with their pectoral flippers in a straight line, which leads to more rigid and stable swimming patterns.
Aquatic reptiles, such as sea turtles, have pectoral flippers to pro-pulse through the water and have pelvic flippers for manoeuvre their bodies. When they swim, they move their pectoral flippers in a clapping motion underneath their body and pull them back up into an airplane position, generating forward motion. A 1993 study found sea turtles minimise drag through the water and increase their swimming efficiency through rotation of their front flipper. They exhibit a natural suite of behaviour skills that help them direct themselves towards the ocean, and identify the transition from sand to water after hatching. A 2003 study found rotation in the pitch, yaw or roll direction gives hatchlings the capability to counteract the forces acting upon them, which allows them to correct with either their pectoral or pelvic flippers and redirecting themselves towards the open ocean.
Discuss terrestrial locomotion of animals with fins and flippers
— Fish: Terrestrial locomotion poses new obstacles such as gravity and new media, including sand, mud, twigs, logs, debris, grass, etc. Fish with fins and flippers are aquatically adapted, hence their appendages don’t use much usage in such environments. Researchers hypothesised that fish try to ‘swim’ on land, but they may have evolved to cope with the terrestrial environment. e.g. Mudskippers demonstrate a 'crutching' gait giving them the ability to walk over muddy surfaces, and dig burrows to hide in. To jump, mudskippers initially manoeuvre their body into a J-curve at about 2/3 of its body length (with its tail wrapped towards the head), then straighten their body to propel them like a projectile through the air. This enables them to cope with the new environment and opens their habitat to new food sources as well as new predators.
— Marine reptiles: Reptiles, such as sea turtles spend most of their lives in the ocean. However, one aspect of their life cycle involves females coming ashore to lay their nests on the beach. As a result, sea turtle hatchlings emerge from the sand and run toward the water by themselves. Depending on the species, Wyneken (1997) described sea turtles as having either a symmetrical gait (diagonally opposite limbs are moving together) or an asymmetrical gait (contra-lateral limbs move together). e.g. Loggerhead sea turtle hatchlings exhibit symmetrical gait on sand, whereas, leatherback sea turtles exhibit the asymmetrical gait on land. It’s known leatherbacks employ their front (pelvic) flippers more to achieve forward terrestrial locomotion. Sea turtles typically nest on subtropical and tropical beaches worldwide and exhibit such behaviour such as arribada (collective animal behaviour). This behaviour is seen in Kemp Ridley’s turtles, which emerge all at once in one night only onto the beach to lay their nests.
How do escape reactions work?
Some arthropods, such as arthropods and shrimps, flick their tail to propel themselves backwards quickly, known as lobstering or the caridoid escape reaction. Varieties of fish, such as teleosts, also use ‘fast-starts’ to escape from predators. Fast-starts are initiated by muscle contraction on one side of the fish twisting the fish into a C-shape. Then muscle contraction occurs on the opposite side to allow the fish to enter into a steady swimming state with waves of undulation traveling alongside the body. Fast-twitch muscle fibres located in the central region of the fish generates that power of the bending motion. Fish have sets of Mauthner cells that signal the muscles on one side of their body to contract. They are activated upon a startling stimuli, which can be visual or sound-based.
Fast-starts are split up into 3 stages:
(I) Preparatory Stroke = Initial bending to a C-shape with small delay caused by hydrodynamic resistance
(II) Propulsive Stroke = Rapid bending of the body to the other side, which may occur multiple times
(III) Rest Phase = Fish returns o normal steady-state swimming and the body undulations begin to cease.
Because larger muscles located closer to the central portion of the fish are stronger, they generate more force than the muscles in the tail. This asymmetry in muscle composition causes body undulations that occur in Stage 3. There’s unpredictability in the fish’s position upon completion of the fast-start, which helps them survive against predators.
Resistance within the inertia of each body part limits the rate of bending of the body. Because the inertia results from the momentum created against the water, this assists the fish in creating propulsion. The forward propulsion generated from C-starts, and steady-state swimming, is a result of the body of the fish pushing against the water. Waves of undulation create rearward momentum against the water, which provide the forward thrust required to push the fish forward.
What is the efficiency of swimming?
The Froude propulsion efficiency is defined as the ratio of power output to the power input:
nf = 2U1 / (U1 + U2)
- where U1 = free stream velocity and U2 = jet velocity.
Efficiencies between 50-80% for carangiform propulsion is interpreted as good.
— Drag Minimisation
Flow disruptions around the body generates pressure differences outside the boundary layer of swimming organisms. This difference on the up- and down-stream surfaces of the body is called ‘pressure drag’, creating a downstream force on the object. On the other hand, fictional drag results from fluid viscosity in the boundary layer, which is elevated by turbulence.
The relationships between inertial and viscous forces in flow ((animal's length x animal's velocity)/kinematic viscosity of the fluid) is measured by Reynolds Number (Re). Higher Re values correlates with higher turbulent flow, where the boundary layer separates and creates a wake. On the other hand, lower Re values correlates with laminar flow, where boundary layer separation is delayed. This decreases wake and kinetic energy loss to opposing water momentum.
Factors that influence drag include:
- Body shape of the swimming organism = Long, slender bodies reduce pressure drag by streamlining, while short, round bodies reduce frictional drag. Therefore, the optimal shape of an organism depends on its niche. Swimming organisms with a fusiform shape will likely experience the greatest reduction in both pressure and frictional drag.
- Wing shape = Different methods of stroke, recovery of the pre-stroke position accumulates drag.
- High-speed ram ventilation = This creates laminar flow of water from the gills along the body of an organism.
- Mucus secretion = Along with the addition of long-chained polymers to the velocity gradient, this can reduce frictional drag experienced by the organism.
— Buoyancy
Many aquatic/marine organisms have developed organs to compensate for their weight and control their buoyancy in the water. They position the density of their bodies adjacent to the surrounding water. Some hydrozoans, such as siphonophores, has gas-filled floats:
- Nautilus, Sepia, and Spirula (Cephalopods) have chambers of gas within their shells.
- Most teleost fish and lantern fish (Myctophidae) have swim bladders.
Many aquatic and marine organisms may also be composed of low-density materials:
- Since deep-water teleosts lack a swim bladder, they have few lipids and proteins, deeply ossified bones, and watery tissues that maintain their buoyancy.
- Some sharks’ livers are composed of low-density lipids, such as hydrocarbon squalene or wax esters (also found in Myctophidae without swim bladders), which provide buoyancy.
Swimming animals whose density is higher than water must generate lift or adapt a benthic lifestyle. Generation of movement-based hydrodynamic lift is important to prevent the fish from sinking. Their bodies often act as hydrofoils, which is more effective in flat-bodied fish. At small tilt angles, lift is greater for flat fish than it is for narrow-bodied fish. Narrow-bodied fish use their fins as hydrofoils while their bodies remain horizontal. Sharks have a
heterocercal-shaped tail to drive the water downward, which creates a counteracting upward force while thrusting the shark forward. The pectoral fins and upward-angle body positioning contributes to the generation of lift. Alexander McNeill believes tunas primarily use their pectoral fins for lift.
Buoyancy maintenance is metabolically expensive, that is, large amounts of energy is required to grow and sustain a buoyancy organ, adjust the composition of biological makeup, and exert physical strain to stay in motion. In 1992, Alexander McNeill suggested swimming upward and gliding downward, in a "climb and glide" motion minimises lower energy costs to physically generate lift, compared to constant swimming on a plane.
— Temperature
Temperature affects both the properties of the water and the organisms in the water, since most organisms have an ideal temperature range specific to their body and metabolic needs. This greatly affects the ability to move through water.
Q10 (Temperature coefficient) = The factor by which a rate increases at a 10 °C increase in temperature. This coefficient is used to measure how organisms' performance relies on temperature. Most organisms’ rates increases as water temperatures increase, but some organisms have limits to this, thus formulate ways to alter such effects, such as by endothermy or earlier recruitment of faster muscle.
For example, Crocodylus porosus, or estuarine crocodiles, were found to increase swimming speed from 15 °C to 23 °C and then to have peak swimming speed from 23 °C to 33 °C. However performance began to decline at temperature higher than 33 °C. This demonstrated a limit to the range of temperatures at which this species could ideally perform.
— Submergence
Energy expenditure is inversely proportional to the animal’s body volume being submerged while swimming. It’s estimated swimming on the surface required 2-3 times more energy than when completely submerged. The bow wave formed at the front when the animal is pushing the surface of the water when swimming creates extra drag.
Discuss the secondary evolution of aquatic locomotion
When tetrapods evolved onto the land, they lost many of their natural adaptations to swim, but many have re-evolved the ability to swim or returned to a completely aquatic lifestyle. On multiple occasions, aquatic animals have re-evolved from terrestrial tetrapods. Examples include:
- Amphibians = Newts
- Reptile = Crocodiles, Sea turtles, Ichthyosaurs, Plesiosaurs, Mosasaurs
- Marine mammals = Whales, seals, otters
- Birds = Penguins
Among invertebrates, a number of insect species adapted characteristics of aquatic life and locomotion. Examples include:
- Aquatic insects = Dragonfly larvae, Water boatmen, Diving Beetles
Some aquatic spiders demonstrate aquatic adaptations but they tend to prefer other modes of locomotion under water than swimming proper.
Some dog breeds swim recreationally e.g. Umbra, a world record-holding dog, can swim 4 miles (6.4 km) in 73 minutes, which places her in the top 25% in human long-distance swimming competitions. Although most cats despise water, adult cats are decent swimmers such as the fishing cat, which has webbed digits. e.g. Turkish Van.
Although lions have been observed to swim, tigers and jaguars are the only big cats known to swim readily. Other animals observed to swim include horses, moose, elk, elephants, camels (e.g. dromedary and Bactrian camels), rabbits (both domestic and wild), guinea pigs (or cavy), mice, snakes (e.g. anacondas) and monkeys (e.g. Proboscis monkey, crab-eating macaque, rhesus macaque).
How do humans swim?
https://en.wikipedia.org/wiki/Swimming
In the context of humans, swimming is a self-propelled locomotion through water, usually for recreation, sport, exercise, or survival. It is achieved through coordinated movement of the limbs, the body, or both. Humans generally hold their breath underwater and undertake rudimentary locomotive swimming within weeks of birth, as a survival response.
The human body needs to be neutrally buoyant in order to swim. On average, the human body has a relative density of 0.98 compared to water, which causes the body to float. However, buoyancy depends on the basis of body composition, lung inflation, and water salinity. Higher levels of body fat and saltier water both lower the relative density of the body and increase its buoyancy.
Since the human body’s density is less than water’s density, water supports the weight of the body during swimming. As a result, swimming is “low-impact” compared to land activities such as running. Objects moving through the water are hindered by resistance caused by the water’s density and viscosity. This resistance is used by swimming strokes to create propulsion, whilst it also drags on the body. Understanding the hydrodynamics is important to stroke technique for faster swimming locomotion. Thus swimmers who want to swim faster or exhaust less try to reduce the drag of the body's motion through the water. To be more hydrodynamic, swimmers can either increase the power of their strokes or reduce water resistance. This means power must increase by a factor of 3 to achieve the same effect as reducing resistance. Being in a horizontal water position, rolling the body to reduce the breadth of the body in the water, and extending the arms as far as possible to reduce wave resistance are criteria in minimising water resistance in order to achieve maximally efficient swimming. Swimmers are known to perform warmup exercises such as squatting to enhance their thigh muscles before plunging into the pool.
How do infants swim?
From newborn until the age of approximately 6 months, human babies demonstrate an innate swimming or diving reflex, which is seen in other mammals. The diving response involves apnea, reflex bradycardia, and peripheral vasoconstriction. Basically, babies immersed in water spontaneously hold their breath, slow their heart rate, and reduce blood circulation to the extremities (fingers and toes). Because infants are innately able to swim, swimming programs offer classes for babies of about 6 months old. This helps build muscle memory and makes strong swimmers from a young age.
Describe the swimming technique
https://www.youtube.com/watch?v=nAPI9lWjgL8
Swimming can be undertaken using a wide range of styles, known as ‘strokes’, which are used different purposes, or to distinguish between classes in competitive swimming. Defined strokes for propulsion through the water aren’t necessary, so untrained swimmers may use a ‘doggy paddle’ of arm and leg movements, similar to the way four-legged animals swim. Human swimming consist of a continuous specific body motion or swimming stroke to propel the body forward. The 4 main strokes used in competition and recreation swimming include ‘front crawl’ (freestyle), breaststroke, backstroke and butterfly. Breaststroke and butterfly stroke are undulating strokes, while front crawl and backstroke are alternating strokes. Most strokes involve rhythmic and coordinated movements of all major body parts — torso, arms, legs, hands, feet, and head, which are synchronised with breathing. However amputees (paralympians) and paralytics train to swim with missing arms or legs.
i. Front Crawl
= Arms alternate while the legs perform a flutter kick, with face looking downwards. It is the fastest style for swimming on the surface.
- Dolphin crawl = Similar to front crawl, but with a dolphin kick. It involves 1 kick per arm or 2 kicks per cycle. This style of front crawl is often used in training.
- Catch up stroke = This variation involves 1 arm always resting at the front while the other arm performs one cycle. This is often used as a drill in training in competitive swimming.
- Head-high crawl = Water polo stroke, lifeguard approach stroke, or Tarzan drill — Used for water polo, by lifeguards to keep the victim in sight, or for those to see where they’re swimming towards and breathe with ease. This variation involves keeping the head above the water, and is typically used as a drill when training in competitive swimming.
ii. Trudgen
= Similar to the front crawl, except that it is paired with a scissors kick, seen in the sidestroke.
- Trudgen crawl = This variation involves a flutter kick (up and down leg kick) between the scissor kicks.
- Double trudgen = This variation involves alternating sides of the scissors kick.
- Double trudgen crawl = This variation of the double trudgen involves alternating flutter kicks between the scissors kick.
iii. Butterfly Stroke
= This stroke is performed face down in the water with a dolphin kick, while the arms move in a forward circle simultaneously.
- Slow butterfly = Moth stroke — This variation involves an extended gliding phase, in which breathing takes place during the pull/push phase, and the heads returns into the water during the recovery phase. It requires 2 kicks per cycle.
iv. Breaststroke
= This stroke is performed face down in the water without rotating the torso. The arms move synchronously underwater, while the legs perform a whip kick. Although the head usually dips in and out, it is possible to keep the head above the water throughout the stroke.
- Inverted Breaststroke = This variation involves a breaststroke kick and arm motions.
v. Backstroke
= This stroke is performed lying on your back. It involves 1 arm reaching behind the head with a fingertip entry while the other arm is by the side, while the legs perform a flutter kick.
- Elementary backstroke = This variation involves synchronised arm movement (beginning with an airplane-like movement, then moving beside the body like a soldier, before finally running up the sides and back out to an airplane position) with a whip kick.
- Inverted Butterfly = This is similar to the elementary backstroke, except it involves a dolphin kick, in which is often used for training purposes.
- Back double trudgen = This variation involves a scissors kick to alternating sides.
- Old English Backstroke = This variation involves the body lying on the back, breaststroke legs and butterfly arms.
vi. Forward Backstroke
= This variation is performed lying on your back and floating. Yours arms are parallel to the water surface, but your movement is opposite to that of a conventional backstroke.
vii. Sidestroke
= This stroke involves you being on your side, pulling the water as if it were a rope with your arms going out and stopping in the middle. This ensures the strokes are most hydrodynamic when moving towards the desired destination, as it pushes the most water when moving away from the location. Moreover, your legs perform a sideways scissors kick.
- Lifesaving Stroke = This variation involves merely bottom arm movements, while the top arm tows a swimmer in distress.
- Combat sidestroke = Developed and used by the United States Navy SEALs, it was designed to be more efficient and minimise profile in water.
viii. Composite Stroke
= This is a drill stroke within 1 basic stroke, ins, or between 2 basic strokes, weens, that builds strength and effort. Example of ins include Front crawl flutter/scissor Dolphin/Dolphin flutter and example of weens include Over arm 1 Arm Lead Sidestroke to 2 Arms Lead Dolphin.
ix. Dog Paddle
= This involves the face hovering over the water and paddling with alternate hands, often with the nose and mouth above the water. It can be used in reverse to propel the body feet first.
- Human stroke = This variation involves the arms reaching out more and pulling farther down.
x. Survival travel stroke
= This stroke involves alternating under arm movements with 1 cycle for propulsion, and 1 cycle for a life to stay on the surface. Since any stroke on the breast can be used, there is no requirement for lifting or turning of the head for breathing.
xi. Breast feet first strokes
= This stroke involves legs extending, then the arms are used to push, flap, clap or uplift.
xii. Snorkelling
= This requires a snorkel to swim on the breast, which is usually combined with masks and fins.
xiii. Finswimming
= This involves a swimmer using fins either on the water surface or underwater to train their swimming technique.
ixx. An arm and a leg
= This involves a swimmer clasping 1 leg with the opposite arm, and using breaststroke movements with the remaining arm and leg.
xx. Flutter back finning
= This is a symmetrically underwater arm recovery with flutter kick.
xxi. Flicker kick
= This involves oscillation of both hands and legs with slight deviation of arms within regular undulation, producing undulating waves (horizontal instead of vertical). Movement is initiated by the shoulders gliding backward and curve, then meandering is transmitted to the hips and legs. This generates undulation between the shoulders and thighs. At the end of the swimming cycle, legs produce flicker kick as collateral to undulatory movement like an eel stroke.
xxii. Feet first swimming
= This stroke is performed on your back with a breaststroke movement of the arms propelling the body forward feet first. The arms are also lifted out of the water and pulled backwards together with a scooping movement. The arms can also be raised behind your head, alternately or together pushing with the hands, propelling the body. Similarly, the hands can be brought together in a clapping action.
xxiii. Eel style
= At the beginning, the swimmer’s starting position is backward, hands to body and legs close floating. Then they begin to undulate initially with their head and shoulders, before trespassing undulation on legs. Hand movements generate most of the propulsion force, which always remain close to the swimmer’s body. They then relay on gliding flow of water in order to achieve easy and swift movement. The legs don’t perform the flutter stroke because that generates an opposing force to undulation. Undulation of the whole body intermittently and at intervals lead to maximal efficiency. Upon the body’s introduction in undulation, optimal velocity is reached. Generating gliding flow is the main purpose of transferring from preparation to propulsion phase, which is utilised by the swimmer as an additional lift to move forward and up. In nature, swimmers use body undulations to generate these propulsive and manoeuvring forces.
ixxx. Corkscrew swimming
= Also known as the Newfie Stroke( referring to Newfoundland, this stroke involves alternating arm movements between front crawl and backstroke, which leads to a constant rotation of the swimmer. When a corkscrew swimmer rotates every 3rd stroke, they are performing a ‘waltz crawl’.
xxx. Gliding
= This involves stretching the arms at the front, the head between the arms and the feet to the back. This creates a streamlined shape to minimise resistance and allow the swimmer to glide. e.g. A start followed by a push off from a wall, or to rest between strokes.
xxxi. Sepia bone
= This involves hand movements to navigate the stream, and to steer and float in the fast flow.
xxxii. Turtle stroke
= On the breast, the right arm is extended then pulled, then the left leg is pushed (while opposite limbs are recovering). Next, the opposite limbs repeat this locomotion. This requires muscles of the waist, and the head can easily be above or below water.
xxxiii. Octopus stroke
= This involves the swimmer beginning from the floating posture backward, spreading their arms and feet. Then their arms are raised further up to the maximum momentum, keeping them parallel to the surface. In the propulsive phase returning the same way, the hands return to the leg axis, then cling to the legs.
A number of strokes are only used for special purposes, e.g. to manipulate an object (a swimmer in distress, a ball), or just to stay afloat. They are:
i. Underwater swimming
= Any style with underwater recovery can be done underwater for certain distances depending on the need for air. When underwater swimming is performed on the back, water can enter a swimmer’s nose. To avoid this, the swimmer uses a nose clip or breathe out through the nose, or use their upper lip or compressor naris muscles to close their nostrils.
- Dolphin kick = Used at the beginning of a swimming race, it allows the swimmer to maintain the speed generated by pushing off the walls at the start and the turns. The feet kick while the arms keep still while extended in front of the head, with the hands together.
- Fish kick = This variation of the dolphin kick is performed on the swimmer’s side. This creates vortices going sideways propelling the swimmer forward unobstructed.
- Pull-down Breaststroke = This stroke has the least energy expenditure, which mainly applies to achieve dynamic apnea.
- Sea lion stroke = This stroke is performed with sculling, meaning the arms are positioned at the side along the bodyline and strongly supported with flutter kicks in a contralateral sequencing. It is most effective swimming through narrow underwater places.
ii. Undulatory swimming
= A 1978 study concluded that undulatory median-paired fin anguilliform is a viable alternative to body-caudal fin anguilliform techniques in terms of swimming hydrodynamics, which includes variables such as buoyancy, gliding, and floating. Based on the hydrodynamic properties of cephalopods as implied to human kinetics, medusoid and anguilliform are demonstrated to elicit low Reynolds Number, low viscous forces, stability, great laminar flow, linear momentum, and efficiency velocity.
iii. Lifesaving strokes
= This variation of the side stroke involves only bottom arm movement while the top arm tows a swimmer in distress.
- Lifesaving approach stroke = Head-up front crawl or Tarzan stroke — This variation of the front crawl involves the eyes directed towards the front above the water level, such as to observe the surroundings searching for swimmers in distress or a ball.
- Pushing rescue stroke = This stroke helps to assist a tired swimmer, who is laid on their back and the rescuer swims a breaststroke kick and pushes against the soles of the tired swimmer.
- Pulling rescue stroke = his stroke helps to assist a swimmer in distress. It involves both swimmers lying on their back, and the rescuer grabs the armpits of the swimmer in distress and performs a breaststroke kick (on the back) for forwarding motion. The kick has to be adequately shallow to avoid hitting the swimmer.
- Extended arm tow = This is a sidestroke or breaststroke on their back, with the rescuer holding the unconscious victim’s head with a straight arm. Their hand cups underneath the chin to ensure that the mouth and nose are out of the water.
- Arm tow = This involves the rescuer performing a sidestroke. Behind the victim holds the upper right arm of a victim with their left hand or vice versa, lifting the victim out of the water.
- Vice grip turn and trawl = This technique is used on a victim with a suspected spinal injury. The lifeguard slowly and carefully approaches the victim (who is usually face down in water), then places 1 hand on the victim's chin, with the ipsilateral arm pressed firmly against the victim's chest. The other hand is placed on the back of the victim's head with the contralateral arm down the victim's back. Both arms press together (like a vice), and the lifeguard uses his feet to begin moving forward and then rolls under the victim to come up alongside her or him, but with the victim now on his or her back. This is one of the hardest lifesaving maneuvers, as the grip must be perfect on the first attempt. Any mistake can give the victim further spinal damage, such as paralysis.
- Clothes swimming = This technique is used when the swimmer is wearing clothes that restrict movement when wet, i.e. almost all clothes. Lifeguards perform it to practice situations where the swimmer fell in the water dressed or the rescuer did not have time to undress. Due to the restricted movement and the weight of wet clothes out of the water, it is not possible tp perform an overarm recovery. Therefore, most swimmers swim breaststroke, but any stroke with underwater recovery is feasible.
- Rescue tube swimming = The lifeguard pulls a flotation device, which is pushed forward when approaching the victim.
iv. Without forward motion
- Survival floating = Dead man float or drownproofing — This involves the swimmer lying on the prone (face down in water) with minimal leg movement, and staying afloat with the natural buoyancy. They lift their head to breathe only then back to floating, in order to stay afloat and rest.
- Back floating = This variation of survival floating is performed on the back.
- Treading water = In the water, the swimmer has their head facing upwards and feet downwards.
- Sculling = Used in surf lifesaving, synchronised swimming, water polo and treading water, this involves a figure 8 movement of the hands for forward motion or upward lift
- Turtle float = This involves raising the knees to the chest and encircling them with the arms.
- Jellyfish float = This holds the ankles with the hands.
- Head first surface dive
I’ll delve into the history, purpose, risk, clothing, equipment and lessons of human swimming in another post.
— Swimming
Animals, especially fish, stay afloat in water by being buoyant. This is possible when the animal’s body has lower density than water. Maintaining a vertical position requires minimal energy, but energy expenditure increases for locomotion in the horizontal plane compared to less buoyant animals. Efficient aquatic locomotion is dependent on the animal’s morphology in order to carry the most essential and basic functions such as catching prey. Many aquatic animals have a fusiform, torpedo-like body form, which gives them a diverse range of locomotive functions. Examples include sharks, whales, dolphins and swordfish. Note that the drag encountered in water is greater than in air.
- Fish primarily generate forward thrust through side-to-side oscillations of their body, with the resulting wave motion ending at the larger tail fin. In order to achieve slower movements, finer control is achieved with thrust from pectoral fins (or front limbs in marine mammals).
- Some fish use their pectoral fins primarily for locomotion known as “labriform swimming”. Examples of such fish include the spotted ratfish (Hydrolagus colliei) and batiform fish (electric rays, sawfishes, guitarfishes, skates, stingrays). On the other hand, marine mammals oscillate their body in a dorso-ventral direction (up-and-down) to generate forward thrust.
- Other aquatic animals, such as penguins and diving ducks, perform “aquatic flying” underwater which generates thrust by flapping their wings backwards in a flying motion. Some fish, such as the slow-moving seahorses and Gymnotus, propel themselves without any wave motion of their body.
- Other animals, such as cephalopods, use jet propulsion to swim rapidly by absorbing water and then propelling it back out through its orifice in an explosive burst.
- Other swimming animals predominantly rely on their limbs to swim, like how humans swim. For example, terrestrial animals like fully aquatic crustaceans return to their aquatic lifestyle on many a occasion.
- Sometimes dolphins ride on the bow waves created by boats or surf on naturally breaking waves.
— Benthic
= Movement by animals living on, in, or near the bottom of aquatic environments. This means many animals walk on the seabed in oceans. Echinoderms primarily use their tube feet to move around the sea bed. Their tube beet typically have a suction-pad like tip that generates a vacuum through muscle contraction. Accompanied by secretion of sticky mucus, this combines with tube feet muscle contractions to provide adhesion. Waves of tube feet contractions and relaxations allow echinoderms to move along u6the adherent surface slowly. An example of an echinoderm is a sea urchin, which use their spines for benthic locomotion.
https://en.wikipedia.org/wiki/Animal_locomotion_on_the_water_surface
(1) Those whose weight is supported by the surface tension at rest, and can therefore easily remain on the water's surface without much exertion.
(2) Those whose weight is not supported by the water's surface tension at rest, and must therefore exert additional motion in a direction parallel to the water's surface in order to remain above it.
- The basilisk lizard or ‘Jesus lizard’ runs across the water surface because its weight is larger than the surface tension can support.
- The western grebe runs across the water surface as part of a mating ritual.
- Animals living on the surface of water such as the water strider, Polyrhachis sokolova and pygmy gecko (Coleodactylus amazonicus) and have hydrophobic feet that help prevent them from breaking the surface tension and getting wet. Biophysicist David L. Hu inferred at least 342 species of water striders. The length of the legs of water striders were directly proportionally to their body size. For instance, the legs of Gigantometra gigra are over 20 cm, which requires a surface tension force of about 40 mN. Water striders shed vortices in the water by creating a series s of "U"-shaped vortex filaments is created during the power stroke to generate thrust. The 2 free ends of the “U”-shaped vortex filaments attach themselves to the water. They transfer adequate backward momentum to the water to generate forward propulsion.
— Meniscus Climbing = The slope of the meniscus at the water’s edge is a difficult climb for water-walking insects if they solely use their usual propulsion mechanism. In order to the pass from the water surface to land, these insects assume a fixed body posture to deform the water surface and generate capillary forces that propel them up the slope (in a quasi-static configuration) without moving its appendages.
— Marangoni Propulsion = This method of locomotion involves insects releasing a surfactant and propel themselves using the Marangoni effect. e.g. Microvelia use Marangoni propulsion to reach a peak speed of 17 cm/s, which is twice its peak walking speed. David Hu and John W.H. Bush theorised wetting arthropods’ use of Marangoni propulsion is analogous to a soap boat, while non-wetting arthropods transfer chemical to kinetic energy in order to communicate Marangoni stress across the creature’s complex surface layer.
— Velella (By-the-wind sailor) = It’s a cnidarian that uses a sail rather than propulsion for locomotion. They extend small rigid sails into the air to catch the wind and align them along the wind’s direction where they act as an aerofoil. This allows velella to sail downwind at a small angle to the wind.
(b) Terrestrial = On ground or other surfaces, including arboreal, or tree-dwelling
This form of locomotion on land includes walking, running, hopping or jumping , dragging and crawling or slithering. As animals adapted from aquatic to terrestrial environments, it stimulated the evolution of terrestrial locomotion. This brought different challenges than that in water, with reduced friction in place of the effects of gravity. Therefore this strengthened the skeletal and muscular frameworks in terrestrial animals to develop structural support. Elastic potential energy is stored in the animals’ tendons to help overcome inertia, and balance is also important for terrestrial movement on land. There are 3 basic forms of locomotion found amount terrestrial animals:
(a) Legged = Movement using appendages
Vertebrates and arthropods commonly utilise their appendages to move. Aspects of legged locomotion include posture (legs supporting the body), number of legs, and functional structure of the leg and foot.
— Posture = The way the body is supported by the legs
There are 3 types of posture: ‘Sprawling’, ‘semi-erect’ and ‘fully erect’. Depending on the posture’s mechanical advantages, some animals use different postures in different circumstances. There is no detectable difference between stances in terms of energetic cost.
Sprawling = This posture is the most primitive and original limb posture from which the others evolved. The upper limbs are held horizontally, while the lower limbs are held vertically. In larger animals, the angle of their upper limbs is substantially larger. For instance, salamanders drag their bodies along the ground. This posture leads to trotting gaits, which forces the bodies of limbed reptiles and salamanders, platypus and several frog species to flex sideways during movement in order to increase step length. Meanwhile, amphibious fish such as the mudskipper use their sturdy fins to drag themselves across land. Other animal species known to have sprawling posture include invertebrates like arthropods and insects, and some octopus species such as the genus Pinnoctopus. Pinnoctopus use their tentacles to drag their bodies across land a short distance to pursue prey between rockpools. On the other hand, large lizards such as monitor lizards and tegus have a semi-erect or an extremely elevated sprawling posture.
Mammals and birds pertain a fully erect posture, albeit each animal evolved them independently. Their legs are positioned beneath their body, which often associates with the evolution of endothermy. This is because it avoids Carrier’s constraint, therefore allowing prolonged periods of activity. However a 1998 study argued the fully erect stance may not be necessarily the "most-evolved" stance. They discovered a semi-erect stance in the forelimbs of crocodilians, which evolved from its ancestors with fully erect stances as a result of adapting to a mostly aquatic lifestyle, though their hindlimbs are still held fully erect. e.g. The mesozoic prehistoric crocodilians Erpetosuchus is believed to have had a fully erect stance and been terrestrial.
— Number of legs
The number of locomotory appendages varies between animals, and the same animal may use a variable number of legs in different locomotory circumstances. e.g. A hexipedal animal called the springtail performs unipedal movement to hurl itself away from jeopardy using a tail-liked forked rod called a furcula that rapidly unfurls from its underside.
Animals that move and stand on 2 legs are categorised as ‘bipedal’. This includes birds, some species of mammal and lizards and insects. Birds move with either an alternating or a hopping gait. Macropods such as kangaroos and jumping rodents hop, while humans and ground pangolins display an alternating bipedal gait. Cockroaches and lizards run on their 2 hind legs with a bipedal gait.
Terrestrial vertebrate animals with legs except birds including mammals, reptiles and amphibians are mostly ‘quadrupedal’, meaning they walk on 4 legs.
Most insects and hexapods are ‘hexapedal’, meaning they walk on 6 legs. Insect exceptions like the praying mantises and water scorpions are quadrupeds with their front 2 legs modified for grasping, and some butterflies such as the Lycaenifae (blues and hairstreaks) are also quadrupeds, while some types of insect larvae such as maggots are may be legless, or have additional prolegs such as caterpillars (5) and sawflies (9).
Spiders and other related taxonomies are ‘octopedal’, meaning they walk on 8 legs. Meanwhile, terrestrial crustaceans such as woodlice have 14 legs. Some invertebrate species such as velvet worms have several dozen pairs of stubby legs under the length of its body. Centipedes have 1 pair of legs per body segment, thus contains typically from around 50 legs to over 200 legs. Millipedes have the most number of legs with 2 pairs of legs per body segment, thus having between 80 and 400 legs in total e.g. the Illacme Plenipes has up to 750 legs. Animals with numerous legs move them in a metachronal rhythm, giving off the appearance of waves of motion travelling forwards along their rows of legs.
— Structure of the legs and feet
Terrestrial vertebrates such as tetrapods have internal bones in their legs containing externally attached muscles that produces movement. The basic form has the shoulder, knee, and ankle joints, at which the foot is attached to the latter. The fins on amphibious fish are known as “tetrapod” or vertebrate legs, while macropods adapt their tails to function as additional locomotory appendages.
Most vertebrate feet have 5 toes, but some animals have evolved to have fewer toes, and conversely, some tetrapods had numerous toes. e.g. Acanthostega has 8 toes on each foot. The evolution of an animal’s feet is dependent on its needs but their anatomy alters where the animal’s weight is placed.
- Most vertebrates including amphibians, reptiles, and some mammals such as humans and bears, walk on the whole of the underside of the foot, categorising them as plantigrade.
- Many other mammals, such as cats, dogs and birds, walk on their toes, categorising them as digitgrade. Their stride length is directly proportional to walking speed, and they often adept at quieter movements.
- Other animals, such as horses, walk on the tips of their toes, categorising them as unguligrade. This leads to longer stride lengths and thus higher velocities.
- A few mammals, such as the great apes and the extinct chalicotheres, walk on their knuckles
(at least for their front legs), often described as knuckle-walking. Knuckle-walkers use their foot (hand) to gather food and/or climb trees, or swim, as with the platypus.
There are various leg forms among terrestrial invertebrates. Arthropod legs are jointed and supported by hard external armour, with the muscles attached to the internal surface of this exoskeleton. On the other hand, velvet worms have soft stumpy legs supported by a hydrostatic skeleton. Caterpillars have prolegs in addition to their 6 arthropod legs that are similar to those of velvet worms, suggesting they share a distant ancestry.
— Gaits
Gaits are defined as the
order animals place and lift their appendages in locomotion. They are categorised according to their patterns of support sequence. Quadrupeds have classified into walking gaits, running gaits, and leaping gaits. In one system (relating to horses), there are 60 discrete patterns: 37 walking gaits, 14 running gaits, and 9 leaping gaits.
i. Arboreal locomotion (Brachiation)
https://en.wikipedia.org/wiki/Arboreal_locomotion
Describe the biomechanics:
— Diameter = Moving along narrow surfaces during arboreal locomotion results in the centre of mass moving beyond the edge of the branch, causing a tendency to topple over. In addition, foot placement is constrained by the need to make contact with the narrow branch. This narrowness severely restricts the range of movements and postures an animal can use to move.
— Incline = Most branches are oriented at an angle to gravity in arboreal habitats, including being vertical, which is problematic to arboreal animals. When animals ascends on an inclined branch, they have to fight against the force of gravity to raise their body, which adds difficulty to their movement. Conversely, when animals descends, they also fight against gravity in order to control its descent and prevent itself from falling.
— Balance = When animals traverse on horizontal and gently sloped branches, they tend to tip to the side due to the narrow base of support. Narrower branches pose greater difficulties in maintaining balance, while steeper and vertical branches causes backwards pitches or downwards slippages. Branches with larger diameters pose difficulties for animals placing its forelimbs closer to the centre of the branch than its hindlimbs..
— Crossing gaps = Since branches aren’t continuous, arboreal animals need to be able to traverse gaps between branches, or between trees, by reaching or leaping across them, or gliding between them.
— Obstructions = Arboreal habitats typically have branches emerging from ones being climbed on and other branches impinging on the space the animal needs to trundle through. These obstructions impede locomotion of limbed animals, or can be used as additional contact (anchor) points to enhance locomotion of limbless animals such as snakes.
Describe the anatomical specialisations:
— Limb Length (Intermembral Index) = Arboreal animals have elongated limbs that are helpful in crossing gaps, reaching for fruit or other resources, testing the firmness of support ahead, and for brachiation. Some lizard species have shorter limbs to help them avoid limb movement being obstructed by impinging branches.
— Prehensile Tails = Arboreal animals, such as tree porcupines, green tree pythons, emerald tree boas, chameleons, silky anteaters, spider monkeys and possums, use prehensile tails to grasp branches. Spider monkeys and crested geckos use the tip of their tails to grasp branches as it has either a bare patch or adhesive pad to increase friction on the branch surface.
— Claws = They help animals interact with rough substrates and re-orient the direction of forces applied by the animal. e.g. Squirrels are able to climb wider tree trunks as to be essentially flat from its perspective. However, claws can interfere with an animal's ability to grasp smaller branches as they may wrap too far around and prick the animal's own paw.
— Adhesion = This method works best on smoother surfaces. e.g. Tree frogs and arboreal salamanders use wet adhesion that functions either by suction or by capillary adhesion. Geckos use dry adhesion in their specialised toes that utilises Van Der Waals forces to adhere to many substrates, including glass.
— Gripping = Primates have hairless fingertips that function as frictional gripping. They squeeze the branch between their fingertips to generate a frictional force that holds the animal's hand to the branch. This method is dependent on the angle of the frictional force, thus on the diameter of the branch. Branches with larger diameters compromise the gripping ability of primates. Chameleons’ mitten-like grasping feet, as well as birds’ feet, also grip branches when perching or moving about.
— Reversible Feet = Squirrels have evolved highly mobile ankle joints that permit rotation of the foot into a 'reversed' posture, in order to control descent down large diameter branches. This allows the claws to hook into the rough surface of the bark, opposing the force of gravity.
— Low centre of mass = This helps reduce the arboreal animals’ pitching and toppling movement when climbing. Postural changes, altered body proportions and smaller sizes contribute to lower centres of mass.
— Small size = This helps increase the relative size of branches to the animal, lower the centre of mass, increase stability, decrease mass (allowing movement on smaller branches), and efficient movement through more cluttered habitats. e.g. Gliding animals are smaller in size, hence lighter weight, such as the reduced weight per snout-vent length for ‘flying’ frogs.
— Hanging under perches = Some primates, bats and all sloth species hang beneath the branches to achieve passive stability. This make pitching and tipping irrelevant, making loss of grip the only method of falling.
How do animals climb on other environments?
Other habitats such as rock piles or mountains requires animals to apply the same climbing principles as they have inclines, narrow ledges, and balance issues. But more research is required to understand the specific demands of locomotion in these habitats.
Caprid are mountain dwelling creatures that move on steep or virtually vertical rock faces by carefully balancing and leaping on stable spots on the mountain surface. Examples of caprid include the Barbary sheep, markhor, yak, ibex, tahr, rocky mountain goat, and chamois. They’re able to adapt thanks to their soft rubbery pads between their hooves to help them grip the surface, their hooves with sharp keratin rims to help them lodge in small footholds, and prominent dew claws.
A prominent predator of the mountain caprid is the snow leopard, which can leap up to ≈17m (~50 ft). Other spectacular balancers and leapers include the mountain zebra, mountain tapir and hyraxes.
What is Brachiation?
https://en.wikipedia.org/wiki/Brachiation
https://www.youtube.com/watch?v=acy--k7Qww0
Traits critical for brachiation include a short spine (in particular the lumbar spine), short fingernails, long curved fingers, reduced thumbs, long forelimbs and freely rotating wrists. These physical characteristics are largely retained by modern humans including flexible shoulder joints and fingers suited for grasping, which suggest their ancestor was a brachiator. Whereas in lesser apes, these aforementioned characteristics adapted to brachiation. Although great apes don’t exhibit brachiation (except orangutans), studies of human anatomy suggests that brachiation may be an exaptation to bipedalism.
Researchers claimed brachiation influenced the style and order of the behaviour of gibbons, as well as shaped the evolution of their body structure. For instance, gibbons carry their infants ventrally rather than dorsally in other primates. This also impacts on their play activities, copulation, and fighting capabilities. Brachiation was thought to provide gibbons evolutionary advantages such as bimanual suspension in the trees using both hands when feeding. Small primates are unable to bimanually suspend themselves for long periods and the increased mass of larger primates hinders their exploitation of food resources at the ends of branches. Nevertheless, gibbons are able to suspend themselves in trees for significant periods, and stretch their long arms to reach food in terminal branches quite effectively. Furthermore, Kristiaan D’Août and Evie Vereecke postulated brachiation as a peaceful and discreet mode of locomotion relative to quadrupedal jumping and climbing thereby more successfully avoiding predators.
There are 2 types of brachiation:
— Continuous Contact = This involves the primate moving at slower speeds and maintaining contact with a handhold, such as a tree branch. This gait type involves passive exchange between gravitational potential and translational kinetic energies to help propel the animal forward at a low mechanical cost.
Researchers often model continuous contact brachiation as a simple pendulum. It consists of an out-of-phase fluctuation of energy as the moving primate swings between each tree appendage, which is being transformed from potential to kinetic, and vice versa. This involves gravitational acceleration to induce movement in both brachiating primates and swinging pendulum balls. Brachiators utilise their momentum to maximise change in kinetic energy during the downswing and maximise loss of kinetic energy as well as avoid lateral movement during the upswing.
The amount of potential energy transformed into kinetic energy during pendulum-like movement is known as “energy recovery”. Although maintenance of high energy recovery levels during brachiation minimises energy expenditure hence allows swift movement to its destination, this compromises control during locomotion. This increases the risk of missing a handhold resulting in injury or death, which makes it preferable for slower movement with lower energy recovery.
— Ricochetal = This involves primates moving at higher speeds, characterised by a flight phase between each contact with a handhold. It exchanges translational and rotational kinetic energy to generate forward propulsion. Due to this aerial phase, this type of brachiation is similar to bipedal running in humans.
Historians postulated brachiation emerged in our African ancestors approximately 13 million years ago, when larger primates began to learn hanging around by the tree branches. This helped new generations of primates develop important long-term corporal adjustments that still exist in many related species today, including humans.
Along with other specialised locomotor behaviours, brachiation is thought to have evolved from arboreal quadrupedalism, which is an ancestral and common locomotor mechanism among primates according to Manuela Schmidt. This would account for the morphological similarities of the upper limb and thorax between the living apes and humans. C.D. Byron regarded the evolutionary transition to brachiation as a a significant contribution to a hypothetical precursor to the adaptation of bipedal walking in early hominids. This may explain the independent evolution of specialised suspensory behaviour between hominid groups.
John H. Langdon and J.G. Fleagle et al. forwarded the “vertical climbing hypothesis”, stating that vertical climbing is the biochemical link between brachiation and bipedalism in order to predict the approximate time period early brachiating primates transitioned to bipedalism. Early hominins were found to share similar climbing adaptations with present day humans including their distinctive body posture, limb proportions and trunk design. Though these aspects require valid explanations by previous adaptions of climbing behaviours.
How does gliding and parachuting work?
Animals such as the flying squirrel have adapted membranes, such as patagia, to help them achieve gliding flight in order to bridge gaps between trees. Some animals such as Rhacophorus (a “flying frog species”) have adapted toe membranes to slow their descent in the air to achieve parachuting flight, in order for them to fall more slowly after leaping from trees.
How do limbless animals climb?
Animals that have evolved specialised musculature for arboreal locomotion include many species of snake. They use a specialised form of concertina locomotion to move slowly along bare branches, and lateral undulation to move on emerged secondary branches. Therefore, snakes perform highly on small perches in cluttered environments, whereas limbed organisms show peak performance on large performances in uncluttered environments.
What are the names of arboreal animals?
There are numerous arboreal animals, too many to list individually, so the list below are prominently arboreal species and higher taxa:
ii. Hand-walking
https://www.youtube.com/watch?v=kpRfKkganLk
This involves a human moving in a vertically inverted orientation with all their body weight resting on their hands. Their legs can be fully extended, or executed with other variations such as stag, straddle or front splits. Acro dancers and circus acrobatics often hand walk in their athletic performances.
The ability to perform hand stands is a prerequisite to mastering the skill of hand walking, which requires upper body pressing strength in the deltoids and triceps, and enhanced sense of balance and spatial awareness. As the body is inverted during hand walking, this significantly increases intracranial blood pressure. Proficiency in hand walking and development of adequate endurance requires hours of practice though.
Some quadrupeds are known to walk bipedally on their forelimbs, thus able to “hand” walk in an anthropomorphic sense. e.g. The spotted skunk rears up and moves about on its forelimbs to orient its anal glands toward its enemies before spraying the putrid oil. Dogs and sealions can also be trained to walk on their forelimbs for certain performances.
iii. Jumping / Leaping
https://www.youtube.com/watch?v=HK3Ft7eBE1k
https://en.wikipedia.org/wiki/Jumping
This involves an organism or non-living (e.g. robotic) mechanical system propelling itself through the air along a ballistic trajectory. Jumping consists of a relatively longer duration of the aerial phase and a higher angle of initial launch. Some animals primarily jump or hop such as kangaroos and rabbits respectively, while other animals (such as frogs) employ the same locomotion only to escape predators. Jumping is also prominent in various activities and sports including the long jump, high jump and show jumping.
Describe the physics of jumping
Jumping involves applying a force against a substrate, which in turn generates a reactive force that propels the jumper away from the substrate. Substrates able to produce an opposing force can be solid or liquid such as ground or water respectively. e.g. Dolphins perform traveling jumps, while Indian skitter frogs perform standing jumps from water. Jumping organisms are mainly governed by the physical laws of ballistic trajectories and minimally by the aerodynamic forces. Consequently, any movement performed by a bird once airborne is not considered as jumping, as initial jumping conditions no longer dictate its flight path.
Once a jump initially launches, the moment it loses contact with the substrate, it will traverse a parabolic path. The launch angle and initial launch velocity determines the travel distance, duration, and height of the jump. Launch angles of 45 degrees yields the maximum possible horizontal travel distance, while launch angles between 35 and 55 degrees yields up to 90% of the maximum possible distance, assuming air resistance is identical for both scenarios.
Physical work is exerted by living organisms’ muscles (or other actuators in non-living systems), which produces kinetic energy over the course of the jump’s propulsive phase. The key determinants of jump distance and height are mechanical power (work per unit time, J/s) and the distance over which that power is applied (e.g., leg length). Therefore, many jumping animals have long legs and muscles optimised for maximal power according to the force-velocity relationship of muscles, though the maximum power output of muscles is rather limited. Nonetheless, many jumping species circumvent this limitation by gradually pre-stretching their elastic elements, such as tendons or apodemes, which stores work as strain energy. Such elastic elements release that strain energy at higher rate (higher power) than equivalent muscle mass, therefore increasing the launch energy beyond the muscles’ capabilities.
Jumps can be initiated from a stationary position or whilst on the move. A “standing jump” involves all work converted into kinetic energy, which accelerates the body in a single movement. On the other hand, a “moving jump or running jump” involves the introduction of additional vertical velocity at the launch position, while horizontal momentum is largely conserved. This means moving jumps have high energy expenditure than standing jumps, due to the inclusion of horizontal velocity preceding the jump. However, moving jumps do produce longer jumping distances.
I will delve into the mathematics and physics of ballistic trajectories in another post.
What anatomy is used for jumping?
Common anatomical adaptations for jumping are often stimulated at launch, whilst post-launch exertions require aerodynamic forces in order to extend the range or control the jump. This is referred to as ‘gliding or parachuting’. Aquatic jumpers are usually adapted for speed, hence perform moving jumps by swimming towards the water surface at a high velocity. e.g. Mud skippers flick their tail to jump whilst on land.
Terrestrial animals primarily use their leg muscles to propel themselves off the ground. Those with longer legs increase the time and distance over which a jumping animal can push against the substrate, thus allowing more power and faster, farther jumps. Animals with larger leg muscles generate greater force, which results in improved jumping performance. Moreover, jumping organisms with elongated foot and ankle bones possess additional joints effectively contain more segments to the limb, as well as additional length.
A prime example of animal with all 3 jumping elements is the frog. Their legs can be twice their body length and their leg muscles accounts up to 20% of their body weight. Furthermore, they lengthen their foot, shin and thigh, as well as extend their ankle bones into another limb joint, and their hip bones to gain mobility at the sacrum for a 2nd 'extra joint’. This leads to frogs jumping over 50 body lengths, a distance of over 8 feet.
Similarly grasshoppers use elastic energy stored in their body to increase jumping distance. However, their physiological constraints limit its muscle power to approximately 375 Watts per kilogram of muscle. Grasshoppers overcome this limitation by anchoring their legs via an internal "catch mechanism" while their muscles stretch an elastic apodeme (similar to a vertebrate tendon). When the catch is released, this rapidly releases the energy from the apodeme, which is faster than the muscle. This allows the power output to exceed that of the muscle responsible for energy production. This is analogous to a human throwing an arrow by hand versus using a bow. In this analogy, elastic energy (from the bow) is used for the muscles to operate closer to isometric on the force- velocity curve. This allows the muscles to exert work over an extended period of time and thus produce more energy than they otherwise could, while the elastic element releases that work faster than the muscles can.
Jumping can be classified by the manner of foot transfer:
— Jump = Jumping from and landing on 2 feet
— Hop = Jumping from 1 foot and landing on the same foot
— Leap = Jumping from 1 foot and landing on the other foot
— Assemble = Jumping from 1 foot and landing on 2 feet
— Sissonne = Jumping from 2 feet and landing on 1 foot
Leaping gaits, distinct from running gaits, include cantering, galloping and pronging.
Trampolines or half-pipes can convert horizontal velocity into vertical velocity, increasing the height of a jump. Plyometric exercises aim to increase an athlete’s vertical jumping height by employing repetition of discrete jumping-related movements in order to boost speed, agility, and power. A 2006 study found children who are more physically active display more proficient jumping (along with other basic motor skill) patterns. Furthermore, the development of jumping in children is directly proportional with age. As children mature, their jumping capabilities advance in all forms. Because there are less physical differences at younger ages, jumping development is easy to identify in children rather than adults. Adults of the same age may be vastly different in terms of physicality and athleticism making it difficult to see how age affects jumping ability.
iv. Knuckle-walking
https://en.wikipedia.org/wiki/Knuckle-walking
https://www.youtube.com/watch?v=cNV6XY6SrJg
Commonly seen amongst quadrupeds, this involves their forelimbs holding their fingers in a partially flexed posture in order to press their body weight down through their knuckles. Technically, their manus (Latin for hand) distally flexes on context with the substratum. Knuckle-walking has additional functions such as food manipulation and climbing (in gorillas and chimpanzees), opening of social insects’ mounds (by anteaters and pangolins using their large claws), swimming (by platypus’ webbed fingers) to minimise stumbling.
In 2000, anthropologists once believed the common ancestor of chimpanzees and humans engaged in knuckle-walking and humans evolved upright walking from knuckle-walking. However, the discovery of a human-liked hominid descended from the common ancestor of chimpanzees and humans called Ardipithecus Ramidus quashed that theory. Studies of Ar. Ramidus conducted in 2009 found it engaged in upright walking rather than knuckle walking, which suggests chimpanzees evolved knuckle-walking after they split from humans 6 million years ago, and humans evolved upright walking without knuckle-walking.
Common knuckle-walkers include apes (chimpanzees), gorillas, and non-primates such as giant anteaters, platypuses and pangolins.
Chimpanzees and gorillas have a hand-walking posture that gives them the ability to climb trees using their hands and exhibit terrestrial locomotion, while grip and climb using their longer fingers. They also can carry small objects in their fingers as they walk on all fours. Their knuckle-walking involves flexing the tips of their fingers and carrying their body weight down on the dorsal surface of their middle phalanges, as well as holding their outer fingers off the ground. A combination of flexion of their interphalangeal joints and extension of their metacarpophalangeal joints hold their wrist in a stable, locked position during the support phase of knuckle-walking. This positions the wrist perpendicular to the ground and in-line with the forearm. Since the knuckle-walker’s hand carries the entire body weight, both the wrist and elbow are extended throughout the final phase.
Juvenile gorillas knuckle-walk more prominently than juvenile chimpanzees, due to the lack of key features in their hand bones once thought to limit wrist extension during knuckle-walking in chimpanzees. e.g. Capitate and Hamate bones have ridges and concavities that are thought to enhance stability of weight-bearing in knuckle-walkers. So far, all chimpanzees and 2 out of 5 gorilla fossils contain those anatomical features.
In 2009, Kivell and Schmidt identified biochemical and postural distinctions between chimpanzee and gorilla knuckle-walking. Gorillas demonstrate “columnar” knuckle-walking, which is a forelimb posture involving alignment of the hand and wrist joints in a relatively straight, neutral posture. On the other hand, chimpanzees pertain a extended wrist posture. In 1975, Hausfater reported baboons knuckle-walk with an extended wrist posture. In the early 2000s, Richmond, Strait and Begun suggested that fossils attributed to Australopithecus Anamensis and Au. afarensis retained specialised wrist morphology from an earlier knuckle-walking ancestor.
v. Running
https://en.wikipedia.org/wiki/Running
https://www.youtube.com/watch?v=Zb_SizNRUPg
This form of terrestrial locomotion -involves humans and other animals to move rapidly on foot. It is a type of gait distinguishes from walking as it has an aerial phase in which all feet are above the ground (though there are exceptions).
https://www.youtube.com/watch?v=cwKnFSEt_XQ
This links contains photo sequences of human locomotion taken by Eadweard Muybridge.
This link contains Eadweard Muybridge’s 1878 first film of a running horse.
How did running evolve?
It is theorised human running evolved in the early ancestor of humans, the ape-like Australopithecus, at least 4.5 million years ago in which they were able to walk upright on 2 legs. Early humans may have grown into endurance runners when performing persistence hunting of animals, that is, the activity of following and chasing until a prey is too fatigued to flee, succumbing to “chase myopathy”. This activity transformed several anatomical features such as the nuchal ligament, abundant sweat glands, the Achilles tendons, big knee joints and muscular glutei maximi. Comparing to physiological evidence and the natural habits of other running animals, this indicated human running was the most successful hunting method. This likelihood was further vindicated through observation of modern-day hunting practice and scientific investigation of the Narkiokotome Skeleton that supported the Carrier theory.
Religious festivals in various regions such as Greece, Egypt, Asia and the East African Rift introduced the concept of competitive running. One of the earliest records of competitive running dates back to around 1829 BCE, is an Irish sporting festival in honour of the goddess, Tailtiu, called the
Tailteann Games. Myths and legends shrouds the true origins of the Olympics and Marathon running, though the first ever recorded games occurred around 776 BCE, which included running events in Ancient Greece. In Plato’s Cratylus, Socrates “suspected that the sun, moon, earth, stars, and heaven, still gods of many barbarians, were the only gods known to the aboriginal Hellenes.” He “noticed them always moving and running, calling them gods or runners by nature (Thus, Theontas)”.
How does running work?
a. Footstrike
This occurs when the plantar portion of your foot initially contacts the ground. Common footstrike types include forefoot, midfoot and heel strike, which are characterised by initial contact of the ball of your foot, ball and heel of your foot simultaneously and heel of your foot respectively. The hip joint then extends from maximal flexion in the previous swing phase. The knee joint then flexes upon footstrike and the ankle moves anteriorly relative to the body in order to achieve proper force absorption. Footstrike initiates at the absorption phase as forces from the initial contact attenuate throughout the lower extremity. Force absorption continues as your body moves from footstrike to midstance due to vertical propulsion from the toe-off during a previous gait cycle.
Recent research into various forms of running has focused on the differences in terms of potential injury risks and shock absorption capabilities between heel and mid/forefoot footstrikes. In 2012, Daoud showed that heel striking associated with injury rates and impact due to inefficient shock absorption and inefficient biomechanical compensations for these forces. Rather than being absorbed by muscles, forces from a heel strike travel through bones for shock absorption. In 2005, Verdini showed that force is transmitted from the bones to other parts of the body, including ligaments, joints and bones in the rest of the lower extremity all the way up to the lower back, as bones cannot disperse force easily. In 1977, Walter suggested that in order to avoid serious bone injuries, the body elicits certain motions to compensate. Compensatory mechanisms occur in the tibia, knee and hip joints, where internal rotation takes place. In 2000, Bergmann linked excessive amounts of compensation over time to higher risk of injuries in those joints along with muscles involved in those motions. However, Daoud argues a mid/forefoot strike associates with higher efficiency and lower injury risk due to the triceps surae acting as a lever system to absorb forces with the muscles eccentrically rather than through the bone. Ardigo (2008) and Pearl (2012) claim that landing with a mid/forefoot strike properly attenuates shock, allowing the triceps surae to aid in propulsion via reflexive plantarflexion after stretching to absorb ground contact forces, thus aiding in propulsion. In 2007, Hasagewa claimed the presence of variations in self selected footstrike types even among elite athletes. Larson (2011) pointed out the higher prevalence of heel strikers in longer distance events. Cavanagh (1990) argued a greater prevalence of mid/forefoot striking runners in the elite fields, particularly in the faster racers and the winning individuals or groups. While one could attribute the faster speeds of elite runners compared to recreational runners with similar footstrikes to physiological differences, the hip and joints have been ignored when evaluating proper propulsion. This raises the question: How are heel striking elite distance runners able to maintain such high paces with a supposedly inefficient and injurious foot strike technique?
b. Midstance
When your lower extremity limb of focus is in knee flexion directly underneath the trunk, pelvis and hips, you are in midstance. At this point, propulsion begins to occur as both of your hips and knee joint hips extend, and ankle plantarflexes. This continues until your leg is extended behind your body and toe off occurs. This involves your hips maximally extended, and knee both extended and plantarflexed, which results in your body being propelled forwards from this motion. Your ankle/foot leaves the ground as the initial swing begins.
c. Propulsion phase
Studies in 2010 and 2012 focused solely on the absorption phases for the purposes of identifying and preventing injury. The propulsion phase involves your body beginning to move from midstance until toe off. According to the full stride length model, propulsion can be enacted by components of the terminal swing and footstrike. At the end of the terminal swing, your hip joint flexes in preparation for propulsion. This generates the maximal range of motion for your hip extensors to accelerate through and produce force. As your hip extensors change from reciporatory inhibitors to primary muscle movers, the lower extremity is brought back toward the ground, with some assistance by the stretch reflex and gravity. Next are the footstrike and absorption phases, which can have 2 outcomes. This phase is a continuation of momentum from the stretch reflex reaction to hip flexion, gravity and light hip extension with a heel strike, which provides minimal force absorption through the ankle joint. During the mid/forefoot strike, the gastro-soleus complex loads up from the shock absorption to assist in plantar flexion from midstance to toe-off. True propulsion commences as the lower extremity enters midstance. Your hip extensors continue contracting with contributions from the acceleration from gravity and the stretch reflex left over from maximal hip flexion during the terminal swing phase. This pulls the ground underneath the body, thereby pulling the runner forward. During midstance, your knees are beginning to flex due to elastic loading from the absorption and footstrike phases in order to preserve forward momentum. At this point, your ankle joint dorsiflexes underneath the body, either elastically loaded from a mid/forefoot strike or preparing for stand-alone concentric plantar flexion. Studies in 2000 and 2010 have demonstrated all 3 joints perform the final propulsive movements during toe-off. Your plantar flexors plantarflexes, pushing you off from the ground, which returns you from dorsiflexion in midstance. This is caused either by release of the elastic load from an earlier mid/forefoot strike or concentric contraction from a heel strike. Studies have found that during a forefoot strike, both the ankle and knee joints release their stored elastic energy from the footstrike/absorption phase. The quadriceps group/knee extensors fully extends the knee, pushes the body off of the ground. Simultaneously, the knee flexors and stretch reflex pull the knee into the flexed position. This adds to a pulling motion on the ground, leading to the start of the initial swing phase. The hip extensors maximally extend, which adds to the forces pulling and pushing off of the ground. The movement and momentum generated by the hip extensors also contributes to knee flexion and the start of the initial swing phase.
d. Swing Phase
The initial swing action responds to both stretch reflexes and concentric movements to the body’s propulsion movements. Flexion of both hips and knees mark the start of returning the limb to the starting position and setting up for another footstrike. Initial swing ends at midswing, then the limb is positioned directly beneath the trunk, pelvis and hip with the knee joint flexed and hip flexion continuing. As hip flexion continues to the point of the stretch reflex activating the hip extensors, this leads to the beginning of the terminal swing. As the knee swings to the anterior portion of the body, it begins to extend slightly. The running cycle of 1 side of the lower extremity is completed with the foot making contact with the ground with footstrike. Note that each limb of the lower extremity works opposite to the other. That means when 1 side is in toe-off/propulsion, the other side is in the swing/recovery phase preparing for footstrike. The flight phase follows the toe-off and the beginning of the initial swing of 1 side, in which neither extremity is in contact with the ground due to the opposite side finishing terminal swing. Initial swing continues as the footstrike of the 1 hand occurs. The opposing limbs meet with 1 in midstance and midswing, beginning the propulsion and terminal swing phases.
e. Upper extremity function
A 2012 study by Nicola & Jewison found the upper extremity function serves mainly to provide balance in conjunction with the opposing side of the lower extremity. A 2010 study by Hammer found that the movement of each leg pairs with the opposite arm which serves to counterbalance the body, particularly during the stance phase. Seen in elite athletes, their arms move most effectively with the elbow joint at about 90 degrees or less. This involves the hands swinging from the hips up to mid-chest level with the opposite leg, while the humerus moves from being parallel with the trunk to about 45 degrees shoulder extension (i.e. never passes the trunk as the humeral muscles flexes) and with as little movement in the transverse plane as possible. In conjunction with the arm swing, the trunk also rotates to serve as a balance point from which the limbs are anchored. This ensures stability within the trunk motion except for slight rotation as excessive movement would contribute to transverse motion and wasted energy.
g. Stride length, hip and Knee function
Studies in the 1990s identified biomechanical factors associated with elite runners include increased hip function, use and stride length over recreational runners. As running speed increases, ground reaction forces increases, which elite distance runners must compensate for in order to maintain their pace over long distances. Few studies suggested that increased stride length attenuate these forces via increased hip flexion and extension through decreased ground contact time and more force being used in propulsion. Mercer (2002) evaluated that increased propulsion in the horizontal plane decreases impact occurring from decreased force in the vertical plane. As the hip flexes, the hip extensors are activated through midstance and toe-off, producing more force. Leskinen (2009) suggested an association between efficient hip joint function and the difference between world class and national level distance runners. As the range of motion in hip flexion and extension increases, both acceleration and velocity increase. This connects powerful knee extension during toe-off with hip extension, contributing to propulsion. Through the terminal swing phases, stride length increases along with some maintained knee flexion. Lafortune (2006) suggested that due to braking and an increased prevalence of heel striking excessive, knee extension during this phase along with footstrike associates with higher impact forces. Skoff (2004) argued elite runners exhibited some degree of knee flexion at footstrike and midstance in order to eccentrically absorb impact forces in the quadriceps muscle group in the first place. Hammer (2010) extends this concept by explaining that the knee joint proceeds to concentrically contract and aid majorly in propulsion during toe-off as the quadriceps group is capable of produce large amounts of force. Pink (1994) demonstrated that recreational runners increase their stride length through knee extension rather than increased hip flexion as exhibited by elite runners. This suggested the hip flexors provide an intense braking motion with each step and decrease the rate and efficiency of knee extension during toe-off, slowing down speed. Nevertheless, the knee extensors contribute to increasing stride length and propulsion during toe-off, which is often observed in elite runners.
What’s a good running technique?
https://www.youtube.com/watch?v=gsUL3a1CxUQ
i. Upright posture and a slight forward lean
When you lean forward, it places your centre of mass on the front part of the foot. This helps you avoid landing on your heel and facilitate the use of your foot’s spring mechanism, as well as avoid landing on your foot in front of the centre of mass and the resultant braking effect. Although upright posture is essential, it is just as important to maintain a relaxed frame and use the core to keep posture upright and stable. As long as your body is neither rigid nor tense, it helps prevent injury. In 2000, Michael Yessis found the most common running mistakes include the chin tilting upwards and shoulders scrunching.
ii. Stride rate and types
Studies in the 1970s discovered that stride rates are consistent across professional runners, measured to be between 185 and 200 steps per minute. In fact, stride length distinguishes long-distance runners from short-distance runners. Multiplying the cadence (steps per second) by the stride length can evaluate the speed of the runner, which is measured in terms of pace in minutes per mile or kilometre. Sprinters alter their stride length (between short and fast) to bring their legs up in order to stay on their toes, while long-distance runners have more relaxed strides, which vary nonetheless.
I’ll delve into the details of running injuries and events in another post.
vi. Walking = Ambulation
https://en.wikipedia.org/wiki/Walking
https://www.youtube.com/watch?v=l55VO0F1xkM
How did walking originate?
Charles Choi theorised tetrapods began to walk as air-breathing fish were known “walk” underwater, which gave rise to the plethora of land-dwelling life that could walk on 2 or 4 limbs. In the 2005 book Evolution of the Insects, arthropods and their relatives were thought to independently evolve walking several times, especially in insects, myriapods, chelicerates, tardigrades, onychophorans, and crustaceans. Studies in 2018 found members of the demersal fish community known as ‘little skates’ use their pelvic fins to push off the ocean floor to generate forward propulsion. The neural mechanisms responsible for this locomotion may have evolved as early as 420 million years ago, before vertebrates first set foot on land. In 2009, Will Dunham and Katherine Harmon discovered footprints in Kenya that were similar to ancestors of modern humans as early as 1.5 million years ago.
What are the variants of walking?
— Scrambling = This method involves both hands to ascend a steep hill or mountain, making it a sluggish and cautious manoeuvre. It often takes place on narrow exposed ridges or steep terrain where more attention to balance is required than in normal walking.
— Snow shoeing = Snowshoes are footwear specialised for walking in snow, which work by distributing the person’s weight over a larger area to prevent their feet from sinking completely into the snow, known as “floatation”. This walking method involves slightly lifting the snowshoes and sliding the inner edges over each other, therefore it helps avoid the unnatural and fatiguing “straddle-gait”. Rolling your feet slightly is also prominent, which yields an exaggerated stride.
— Beach walking = This sport involves walking on sandy beaches, which can be developed on compact or non-compact sand.
— Nordic walking = This physical activity and sport is performed with specially designed walking poles similar to ski poles. Compared to regular walking, Nordic walking (also called pole walking) involves applying force to the poles with each stride. More of your body would be utilised with higher intensity, which stimulates development of fitness not present in normal walking for the chest, lats, triceps, biceps, shoulder, abdominals, spinal and other core muscles. This may result in significant increases in heart rate at a given pace. Studies estimate Nordic walking increase energy production by 46%, compared to walking without poles.
— Pedestrianism = This sport developed around the late 18th and 19th centuries amongst inhabitants of the British Isles. By the end of the 18th century, feats of of foot travel over great distances gained attention by the growing popular press. In the 19th century, interest and wagering in the sport spread to the USA, Canada, and Australia. By the end of the 19th century, Pedestrianism was largely displaced by the rise in modern spectator sports and by controversial involving rules, limiting its appeal as a source of wagering. This lead to its inclusion in the amateur athletics movement. It was codified in the latter half of the 19th century, then it evolved into ‘racewalking’. By the 19th century, racewalkers were often expected to extend their legs straight at least once in their stride, and obey the “fair heel and toe” rule. Despite its vagueness, it is defined as the toe of 1 foot not leaving the ground before the heel of the next foot touches down. Occasionally, racers were permitted to jog to relieve their cramps, and distance rather than code determined gait for longer races.
— Power walking (Speed Walking) = This act of walking travels typically ranges between 7 and 9 km/h (4.5 and 5.5 mph). This involves at least 1 foot being in contact with the ground at all times.
— Racewalking = This long-distance athletic event involves racewalkers running with at least 1 foot in contact with the ground at all times. Since stride length is reduced, race walkers attain cadence rates comparable to those achieved by Olympic 800-metre runners in order to achieve competitive speeds. They’re required to maintain this effort for long periods at a since (like hours) since there are Olympic events that are 20 km (12.4 mi) (men and women) and 50 km (31 mi) (men only), and 50 mile (80.5 km) long.
— Afghan walking = Formed in the 1980s, this is a rhythmic breathing technique that synchronises with walking. It was based on the observations made by the Frenchman Édouard G. Stiegler, during his contacts with Afghan caravaners, capable of making walks of more than 60 km per day for dozens of days.
Describe the biomechanics of walking
The biomechanics of human walking is based on a double pendulum. During forward motion, the leg leaving the ground swings forward from the hip, known as the ‘first pendulum’. Next, the leg strikes the ground with the heel and rolls through to the toe in a motion, known as an ‘inverted pendulum’. Both of your legs are coordinated in motion so 1 foot or the other is always in contact with the ground. This method recovers approximately 60% of energy used due to pendulum dynamics and ground reaction force.
The word ‘walk’ is derived from the Old English word wealcan meaning “to roll”. In bipedal animals such as animals, walking is distinguished from running as 1 foot is lifted off the ground at a time followed by a period of double-support. Conversely, running involves both feet raised in the air with each step. In quadrupedal animals, since there are numerous gaits referred to as ‘walking’ or ‘running’, it is difficult to correctly classify them mechanically there is inconsistency on the prominence of a suspended phase or the number of feet in contact any time. One way to effectively distinguish walking from running is using motion capture or a force plate at mid-stance to measure the height of a person’s centre of mass. In a walking organism, their centre of mass reaches a maximum height at midstance, whereas it is at a minimum in a running organism. Nevertheless, this distinction holds true for locomotion over level or approximately level ground (below 10% grade). Essentially, the kinetic energy of forward motion is constantly being transferred, increasing potential energy. This mechanism is reversed in running where the centre of mass is at its lowest as the leg is vertical, due to the impact of landing from the ballistic phase being absorbed by bending of the leg. Consequently, this allows energy to be stored in muscles and tendons. In running there is a conversion between kinetic, potential, and elastic energy.
An obvious difference between running and walking is the speed of locomotion. The average walking speed in humans at crosswalks is about 5 km/hr (3.1 mi/hr), though this can vary greatly depending on many factors such as height, weight, age, terrain, surface, load, culture, effort, and fitness. Studies in 1997 and 2005 found pedestrian walking speeds ranged between 4.51 km/hr (2.80 mi/hr) and 4.75 km/hr (2.95 mi/hr) in older individuals, and between 5.32 km/hr (3.31 mi/hr) and 5.43 km/hr (3.37 mi/hr) in younger individuals. Meanwhile, brisk walkers can walk up to 6.5 km/hr (4.0 mi/hr) and champion racewalkers can walk, on average, more than 14 km/hr (8.7 mi/hr) over a distance 20 km (12 mi).
The absolute limit of an individual's speed of walking (in the absence of special techniques such as those employed in speed walking) are dictated by the upwards acceleration of the centre of mass during a stride. If their upwards acceleration is greater than gravitational acceleration, they will become airborne as they vault over the leg on the ground. Nevertheless, animals typically transition to run at lower speeds in order to maximise energy efficiency.
In 2015, Lalit Patnalik;s 2D inverted pendulum model of walking determined at least 5 physical constraints that place fundamental limits on walking like an inverted pendulum. These constraints are take-off constraint, sliding constraint, fall-back constraint, steady-state constraint, high step-frequency constraint.
https://www.youtube.com/watch?v=cVCtWgD8Ngc
This video link shows a video of the human walking cycle recorded by Eadweard Muybridge.
How do other animals walk?
i. Horse gait
https://www.youtube.com/watch?v=mDJ_Saape8s
Horses walk with a 4-beat gait averaging about 6.4 km/hr (4 mi/hr) that follows this sequence: left hind leg, left front leg, right hind leg, right front leg, in a regular 1-2-3-4 beat. During the walking motion, horses always have at least 1 foot raised and the other 3 feet on the ground, save for a brief moment when weight is being transferred from 1 foot to another. They also move their head and neck slightly vertically in order to maintain balance.
Normally, the horses’ advancing rear hoof oversteps the spot where the previously advancing front hoof touched the ground. Smoother and comfortably walks correlates with more larger overstepping of the rear hoof. Though smoothness of walks vary between different breed and individual horses. The lateral forms of ambling gaits such as the running walk, singlefoot, and similar rapid but smooth intermediate speed gaits are the fastest ‘walks’ with a 4-beat footfall pattern.
ii. Elephants
https://www.youtube.com/watch?v=RsEOBnWKkRw
Elephants can move both forwards and backwards, but can’t trot, jump, or gallop. Shoshani et al. found they use only 2 gaits when moving on land, the walk and a faster gait similar to running. When they walk, their legs act as pendulums, with the hips and shoulders rising and falling while the foot is planted on the ground. Because of the absence of an “aerial phase”, their faster gait doesn’t satisfy all criteria of running, despite them using its legs much like other running animals, with the hips and shoulders falling and then rising while the feet are on the ground. Genin et al. found fast-moving elephants run with their front legs, but 'walk' with their hind legs. They can reach speeds of up to 18 km/h (11 mph), which is normal galloping speed for most other quadrupeds, even accounting for leg length.
iii. Walking (Ambulatory) fish
https://www.youtube.com/watch?v=FLh4ODMBGJE
They are able to travel over land for extended periods of time. It can also be applied to other uncommon forms of fish locomotion e.g. fish “walking” along the sea floor, such as handfish or frogfish.
(b) Limbless locomotion = Movement without legs, thus primarily uses the body itself as a propulsive structure.
Terrestrial and amphibious limbless vertebrates and invertebrates move by using their bodies to generate propulsion, which are often referred to as “slithering” or “crawling”. All limbless animals are cold-blooded meaning there are exothermic i.e. No limbless birds or mammals.
— Lower body surface:
Some animals such as snakes or legless lizards move on their smooth underside, Molluscs such as slugs and snails move on a layer of mucus secreted from their underside to reduce friction and protect themselves from injury when moving over sharp objects.
Earthworms have small bristles (setea) that hook into the substrate, which in turn produces movement.
Other animals, such as leeches, have suction cups on either end of the body allowing 2 anchor movement.
— Types of movement:
Some limbless animals, such as leeches, have suction cups on either end of their body, allowing them to move by anchoring their rear end and then moving forward the front end, which is then anchored and then the back end is pulled in, and so on. This is known as
2-anchor movement. E.g. An inchworm uses this movement by using its appendages on either end of its body to clasp the ground.
i. Concertina movement
= This consists of snakes and other legless organisms gripping or anchoring with portions of the body while pulling or pushing other sections in the direction of movement.
Each point on the snake’s body goes through alternating cycles of static contact and movement, with regions propagating posteriorly. This is quite strenuous and slow because it burns more calories per meter compared to either sidewinding or lateral undulation.
When snakes are in unobstructed tunnels, they lack both sufficient contact points to perform lateral undulation and sufficient lateral room to perform sidewinding. Therefore they employ tunnel concertina locomotion to flex its body in a series of alternating bends pressing against the tunnel walls in order to anchor itself. Initially, they straighten those bends by extending the anterior portion of its body, then flexing the same portion to form anterior anchor points while pulling the posterior portion forward. Although this locomotion is slower than lateral undulation or sidewinding, it is fairly fast nonetheless, allowing snakes to move approximately 10% of their length per second. However, because snakes have to straighten and re-form bends, they need the entire space of the tunnel to move at all. Any obstruction would disrupt any tunnel concertina movement. This would enforce snakes to transition to a more faster and economical mode of locomotion. In the case of extreme lateral constraint e.g. tunnel width less than 3x body width, snakes will ignore the contact points that could be used in lateral undulation and perform concertina.
When snakes are on bare branches on trees in the absence of secondary branches, they employ arboreal concertina locomotion. This involves snakes ventrally flexing their body at the points the alternation bends cross the perch in order to grip the branch. Those bends occasionally extend beyond the edge of the branch. Initially, the snake extends the anterior portion of its body, but then it follows a constant path, unlike tunnel concertina locomotion. Then it forms anterior grips and pulls the body forward, exhibiting the characteristic of ‘path following’. This helps snakes avoid any obstacle falling between the bends of the snake’s body. However, this mode of locomotion is sluggish, barely moving faster than 2% of their length per second.
ii. Undulatory movement
= This is characterised by wave-like movement patterns that generate forward propulsion. This gait type is found in crawling in snakes, or swimming in the lamprey. Limbed creatures, such as the salamander, choose to forgo use of their legs in certain environments and demonstrate undulatory movement.
Limbless creatures generate forward undulatory locomotion by propagating flexural waves along the length of their bodies. The forces generated between the animal and the surrounding environment leads to alternating sideways forces acting to propel the animal forward, which generate both thrust and drag.
iii. Rectilinear movement
= Snakes and heavy-bodies species such as terrestrial pythons and boas often exhibit this locomotion, which involves flexion of the body during a turn. Rectilinear locomotion involves 2 opposing muscles, the costocutaneous inferior and superior, located on every rib connecting to the skin. Although ribs are motionless, the muscles and the skin are the main source to generate forward motion. Firstly, the costocutaneous superior muscle lifts a segment of the snake’s belly upwards from the ground, placing it ahead of its former position. Secondly, the costocutaneous inferior muscle pulls backwards while the snake’s belly scales are touching the ground, which propels the snake forwards. These sections of contact propagate posteriorly, resulting in discrete segmental movement of the ventral belly akin to "steps" while the overall body of the snake moves continuously forward at a relatively constant speed.
Although rectilinear locomotion is sluggish (~ 1-6 cm / second), it is also silent and difficult to audibly detect, making it useful for predators when stalking their prey. It is typically used when the space being traversed is too constricting to allow for other forms of movement. When snakes climb, this locomotion is used in conjunction with concertina movements to exploit terrain features such as interstices in the surfaces being climbed.
iv. Sidewinding
= This type of locomotion is unique to caenophidian snakes, which involves movement across loose or slippery substrates. In loose desert sands, common sidewinding creatures include the Saharan horned viper, Cerastes cerastes, sidewinder rattlesnake, and Crostalus cerastus. Whereas in Southeast Asia, Homalopsine snakes use sidewinding to move across tidal mud flats. This method of locomotion is derived from lateral undulation as they share similarities, in spite of appearances. When a snake exhibits lateral undulation, it resembles a sine wave pattern, with straight body segments having either a positive or negative slope. Sidewinding is achieved when all body segments are lifted with the same slope off the ground.
The resultant movement involves the snake’s body in static contact when touching the ground. This throws the head forward, followed by the body, which is lifted from the prior position and forward to lie on the ground in its new position ahead. The snake gradually progresses at an angle, which leaves a series of mostly straight, J-shaped tracks.
Sidewinder rattlesnakes use sidewinding locomotion to increase the proportion of its body contacting the sand. This helps it ascend sandy slopes without slipping and match the decreased yielding force of the inclined sand.
(c) Rolling = Rotation of the body over a substrate.
Although animals have never evolved wheels for locomotion, some roll their whole body to move. These “rolling animals” are divided into those that roll under the force of gravity or wind and those that roll using their own power.
https://en.wikipedia.org/wiki/Rotating_locomotion_in_living_systems
Several organisms demonstrate adaptations for rolling locomotion. Despite their utility in human vehicles, no organism has evolved to develop true wheels and propellers to assist in movement (except for certain flagella, which function like corkscrews). This has baffled biologists as they attempted to expound on the reasons for the apparent absence of biological wheels. The question is “Why hasn’t or can’t life evolve wheels?”. There are developmental and evolutionary obstacles to the advent of a wheel by natural selection in addressing this question.
There are 2 distinct modes of rotation locomotion:
i. Simple Rolling
Rolling organisms don’t constitute the use of a wheel, as they rotate as a whole, rather than employing separate parts which rotate independently. Organisms that form their bodies into a loop to roll are elongated, including certain caterpillars (to escape danger), tiger beetle larvae, myriapods, mantis shrimps, Armadillidiidae, Mount Lyell salamanders. Other species that adopt more spherical postures to protect their bodies from predators include armadillos, Armadillo girdled lizards, fossilised trilobites, hedgehogs, isopods, pangolins and wheel spiders. By altering their shape to generate a propulsive force, these species roll passively (under the influence of gravity or wind) or actively to escape from predators.
https://www.youtube.com/watch?v=dATZsuPdOnM
Found in open plain environments, tumbleweeds separate from their root structure and roll in the wind to distribute their seeds. Well-known tumbleweeds include Kali tragus (Salsola tragus), or prickly Russian thistle, and Fungi of the genus Bovista.
Coming from the Latin for ‘wheel-bearer’, rotifers are a phylum of microscopic multicellular animals that are typically found in freshwater environments. Despite not having any rotating structures, rotifers have a ring of rhythmically beating cilia to feed and propel their body.
Keratinocytes are a type of skin cell that migrate with a rolling motion to a skin wound for healing purposes. They serve to form a barrier against pathogens and moisture loss through wounded tissue.
Dung beetles use their bodies to roll animal excrement into spherical balls by walking backwards and pushing the ball with their rear legs. Phylogenetic analysis interpret this rolling behaviour may have evolved independently several times. This rolling behaviour of beetles was first noted by the ancient Egyptians, whom imparted sacred significance to their activities. Gerhard Scholtz (2008) explained that beetles face many of the same mechanical difficulties that rolling organisms contend with, even though the dung ball is rolling rather than the beetle itself.
ii. Wheels & Propelling motion (Free Rotation) = Spinning on an axle or shaft, relative to a fixed body.
- Macroscopic
Among animals, there is only 1 known example of an apparently freely-rotating structure. It is the crystalline style of certain bivalves and gastropods, which uses rotation for digestion instead of locomotion. The style consists of a transparent glycoprotein rod continuously forming into a cilia-lined sac and extending into the stomach. The cilia rotate the rod to wrap it in mucus strands. In 1980, Jennifer Owen showed that digestive enzymes are released as the rod slowly dissolves in the stomach. It is unclear if the style is rotated continuously or intermittently, as estimates of the speed of rotation of the style in vivo vary significantly.
- Molecular
There are 2 known examples of molecular-scale rotating structures used by living cells. One of which is ATP Synthase, an enzyme used in the process of energy storage and transfer, which functions like a flagellar motor. Falk & Walker (1998) theorised ATP synthase emerged by modular evolution, in which 2 subunits with their own independent functions bound together to gain a new functionality. There is only 1 known example of a biological “wheel”, which involves continuous propulsive torque about a fixed body. The flagellum is a corkscrew-like tail used by single-celled prokaryotes for propulsion. About half of all known bacteria contain at least 1 flagellum, which indicates rotation is the most common form of locomotion in living systems microscopically. At the base of the bacterial flagellum, where it enters the cell membrane, is a motor protein that acts as a rotary engine. It is powered by a proton motive force, by which protons (hydrogen ions) flow across the bacterial cell membrane due to a concentration gradient set up by the cell’s metabolism. For example, the genus Vibrio has 2 kinds of flagella, lateral and polar, and some are driven by a Na+ (sodium) ion pump rather than a proton pump. James Franklin (2009) measured flagella allow bacteria to efficiently move at speeds of up to 60 cell lengths per second. Oster and Wang (2003) illustrated the rotary motor at the base of the flagellum and ATP synthase shared similarities in structure. A 1972 study found Spirillum bacteria have helical bodies with flagella at either end to allow them to spin about the central axis of their bodies as they move through the water.
A group of prokaryotes separate from bacteria known as Archaea (archaella) also feature flagella that are driven by rotary motor proteins. However, these motor proteins are structurally and evolutionarily distinct from bacterial flagella, as they have evolved from type IV pili rather than Type III secretion system.
Some eukaryotic cells, such as the protist Euglena, also have flagella, but they don’t rotate at the base. Instead, they bend in such a way that the tip of the flagellum whips in a circle. An eukaryotic flagellum is also called a ‘cilium’ or ‘undulipodium’, which is structurally and evolutionarily distinct from prokaryotic flagella.
https://www.youtube.com/watch?v=fFq_MGf3sbk
— Gravity or wind-assisted
The web-toed salamander lives on steep hills in the Sierra Nevada mountains, Studies found they often coil itself up into a ball and roll downhill when disturbed or startled.
The pebble toad (Oreophrynella nigra) lives atop tepui in the Guiana highlands of South America. They roll into a ball, typically on an incline, and then roll away under gravity like a loose pebble when threatened, often by tarantulas.
Found in the Namib desert are the Namib wheeling spiders (Carpachne app.), which activity roll down sand dunes. This allows them to successfully escape predators such as the Pompilidae tarantula wasps, which lay their eggs in a paralysed spider for their larvae to feed on when they hatch. The spiders flip their body sideways and then cartwheel over their bent legs to begin the rolling motion. At 1 metre per second, the spider’s rotation is considered fast, with the golden watch spider (Carparachne aureoflava) rolling up to 20 revolutions per second.
Coastal tiger beetle larvae flick themselves into the air and curl their bodies to form a wheel upon a threat. When the wind blows, often uphill, they roll as far as 25 m and as fast as 11 km/h (3 m/s; 7 mph).
Pangolins also roll into a tight ball when threatened. Studies reported them using both gravity and self-powered methods to roll away from danger. In the hill country of Sumatra, a pangolin fled from a researcher (named Tenaza) to the edge of a slope and curled into a ball to roll down the slope, crashing through the vegetation, and covering an estimated 30 metres or more in 10 seconds.
— Self-powered
Pleuroptya ruralis is a caterpillar of the mother-of-pearl moth that touch their heads to their tails and roll backwards when attacked. They roll up to 5 revolutions at about 40 cm per second, which is about 40 times its normal speed.
Nannosquilla decomspinosa is a species of long-bodied, short-legged mantis shrimp that lives in shallow sandy areas along the Pacific coast of Central and South America. When a low tide strands them, the 3 cm stomatopod lies on its back and performs backwards somersaults over and over. It moves up to 2 meters at a time by rolling 20–40 times, with speeds of around 72 revolutions per minute, which is 1.5 body lengths per second (3.5 cm/s). Studies conducted in 2008 estimated that the stomatopod acts as a true wheel around 40% of the time during this series of rolls. The remaining 60% of the time involves thrusting its body upwards and forwards to “jumpstart” a roll.
A researcher in the Serengeti reported pangolins initially could not roll when surrounded by a group of lions that were waiting and dozing. However, with every slight unroll, it gave itself a push to roll some distance before it rolled far enough away from the lions to be safe. This allowed the pangolin to cover distance while still remaining in a protective armoured ball.
Moroccan flic-flac spiders use forward or backward flips similar to acrobatic flic-flac movements to escape from a predator that provoke or threaten them, which doubles their normal walking speed.
- Peristalsis and Looping
Animals moving in terrestrial habitats without the aid of legs include earthworms, leeches and geometer moth caterpillars. Earthworms use peristalsis to crawl, which are rhythmic contractions of muscle. Meanwhile, leeches and geometer moth caterpillars use their paired circular and longitudinal muscles (as for peristalsis) to attach to a surface at both anterior and posterior ends, allowing movement by looping or inching (measuring off a length with each movement). When one end is attached, the other end is then projected forward peristaltically until it touches down, as far as it can reach. Then the first end is released, pulled forward, and reattached, and the cycle repeats. In the case of leeches, attachment is by a sucker at each end of the body.
- Sliding
In icy environments, penguins either waddle on their feet or slide on their bellies across the snow, known as tobogganing, which conserves energy while moving quickly. Some pinnipeds perform a similar behaviour called sledding.
- Climbing
Some animals are specialised for moving on non-horizontal surfaces such as climbing animals in trees. e.g. The gibbon is specialised for arboreal movement , travelling rapidly by brachiation.
Animals living on rock faces such as in mountains require careful balancing and leaping acts to move on steep or even near-vertical surfaces. e.g. The mountain-dwelling caprids (Barbary sheep, ibex, rocky mountain goat, yak, etc.) have a soft rubbery pad between their hooves for grip, hooves with sharp keratin rims for lodging in small footholds, and prominent dew claws. The snow leopard possess spectacular balance and leaping abilities, such as ability to leap up to 17 m (50 ft), to hunt caprids.
Some light animals use suckers to adhere to the surface to climb up smooth sheer surfaces or hang upside down. Many insects as well as geckos perform similar feats.
- Powered cartwheeling
This locomotion involves a series of rapid, acrobatic movements of its legs similar to those used by gymnasts, to actively propel itself off the ground, allowing it to move both down and uphill, even at a steep incline. The Moroccan flic-flac spider (Cebrennus rechenburgi) is an example of powered cartwheeling. It reach speeds of up to 2 m/s using forward or back flips to evade threats.
What are the biological barriers to wheeled organisms?
i. Evolutionary constraints
The processes of evolution may help explain why wheeled locomotion hasn’t evolved in multicellular organisms. Complex structures or systems probably don’t evolve to be wheeled if its incomplete form provides no benefit to the organism. Neo-Darwinism states that adaptations are produced incrementally through natural selection, so major genetic changes will usually spread within populations only if they increase the individuals’ fitness. Although neutral changes (i.e. not provide any benefit) can spread through genetic drift, and detrimental changes can spread under some circumstances, large changes requiring multiple steps will occur only if the intermediate stages increase fitness. Richard Dawkins (1996) described this matter as “unattainable in evolution because it lies [on] the other side of a deep valley, cutting unbridgeably across the massif of Mount Improbable.” In such a fitness landscape, wheels might sit on a highly favourable “peak", but that valley around the peak may be too deep or wide for the gene pool to migrate across by genetic drift or natural selection. Stephen Jay Gould (1981) noted that biological adaptation is limited to working with available components “as animals are debarred from building them by structural constraints inherited as an evolutionary legacy”, despite wheels working well.
Natural selection could explain why wheels are unlikely to solve the problem of locomotion. Even a partially evolved wheel with 1 or more missing key components would probably not impart an advantage to an organism. The flagellum may have evolved from the recruitment of individual components from older structures that performed tasks unrelated to propulsion. Studies in 2006 suggested that the rotary motor (or the basal body) might have evolved from a structure used by the bacterium to inject toxins into other cells. Gould & Jay (1982) described the recruitment of previously evolved structures to serve new functions as ‘exaptation’.
In 2003, molecular biologist Robin Holliday hypothesised that the absence of biological wheels argues against creationist or intelligent design accounts of the diversity of life. His reasoning is the expectation of an intelligent creator to deploy wheels wherever they would be of use, which is free of the limitations imposed by evolution.
ii. Developmental and anatomical constraints
There is no clarity on why vastly different processes of embryonic development are capable of producing a functioning wheel. The interface between the static and rotating components of the whee is regarded as an anatomical impediment to wheeled multicellular organisms. The wheel must be able to rotate freely relative to the rest of the machine or organism either passively or driven. Furthermore they must be able to rotate through an arbitrary angle without ever needing to be “unwound”. Therefore, the wheel cannot be permanently attached to the axle or shaft about which it rotates. This is, the axle cannot be affixed to the rest of the machine or organism if the axle and wheel are fixed together. There are several functional problems created by this requirement:
— Power transmission to driven wheels:
Torque needs to be applied to driven wheels to generate the locomotive force. In animals, the skeletal muscles has to provide this motion by deriving their energy from the metabolism of nutrients from food. However, muscles aren’t capable of directly driving a wheel because they are attached to both of the components that must move relative to each other. A 2003 study concluded that large animals cannot produce high accelerations because inertia increases rapidly with body size.
— Friction:
To minimise wear and prevent overheating on mechanical components, friction must be reduced. As the relative speed of the components as well as the contact force between them increases, the importance of mitigating friction increases. To reduce friction at the interface between 2 components, various types of bearing and/or lubricant can be used. In biological joints, cartilage with a low friction coefficient combined with lubricating (low viscosity) synovial fluid can reduce friction at the knee joint, for instance. Gerhard Scholtz asserted that a similar secreted lubricant or dead cellular material could allow free rotation of a biological wheel.
— Nutrient and waste transfer:
The ability of a wheeled organism to transfer materials across the interface between the wheel and axle (and/or body) is limited. The living tissues making up the wheel must be supplied with oxygen and nutrients, and cleansed of their wastes to sustain metabolism. Animal circulatory systems are typically composed of blood vessels, which are unable to provide transportation across the interface. If there aren’t any blood vessels, oxygen and nutrients would need to diffuse across the interface, which is limited by the available partial pressure and surface area, according to Fick’s law of diffusion. This process would be insufficient and inefficient for large organisms such as humans. An alternative would be a wheel made of excreted, non-living materials such as keratin (the ingredient of hair and nails).
What are the disadvantages of wheels?
Wheels are found to incur mechanical and other disadvantages in certain environments and situations that decrease the fitness of organisms compared to those with limbed locomotion. This suggests that the absence of wheels in multicellular life may not be the “missed opportunity” of biology at first thought, even when biological constraints are discounted. Given the mechanical disadvantages and restricted usefulness of wheels, one would ask “Why do human vehicles not make more of limbs?” The use of wheels instead of limbs in most engineered vehicles such as cars, buses, trucks and trains likely attribute to the design’s complexity required to construct and control limbs, rather than to a consistent functional advantage of wheels over limbs.
Discuss the efficiency of the wheel
— Rolling Resistance:
W = Weight of the wheel plus the supported portion of the vehicle
F = Propulsive force
r = Wheel radius
Although stiff wheels are more energy efficient than other means of locomotion when travelling over hard, level terrain (such as paved roads), they are inefficient on soft terrains such as soil, due to their vulnerability to rolling resistance. As vehicles roll on a surface, they lose energy to the deformation of its wheel, a phenomenon known as ‘rolling resistance’. Since softer surfaces deform more and recover less than surfaces, this results in greater rolling resistance, and smaller wheels are especially susceptible to this effect. Rolling resistance is medium to hard soil is measured at 5 - 8 times greater than on concrete, and 10 - 15 times greater on sand. While wheels deform the surface along their entire path, limbs, on the other hand, induce a small, localised deformation around the region of foot contact.
Rolling resistance is a major factor in the abandonment of wheels by at least 1 historical human civilisation. Wheeled chariots were commonly used in the Middle East and North Africa during the existence of the Roman Empire. Upon the collapse of the Roman Empire and disrepair of roads, local populations transitioned from wheels to camels to transport their good in the sandy desert climate. Stephan Jay Gould asserted that, in the absence of maintained roads, camels required less manpower and water than a cart pulled by oxen.
— Efficiency of aquatic locomotion:
Rotating systems moving through a fluid carry an efficiency advantage only at low Reynolds numbers (i.e. viscosity-dominated flow). e.g. Bacterial flagella. On the contrary, oscillating systems have an advantage at higher (inertia-dominated) Reynolds numbers. Efficiencies of ship propellers and aircraft propellers are typically around 60% and 80% respectively. Using an oscillating flexible foil such as a fish tail or bird wing can increase the efficiency to 96-98%.
— Traction:
When wheels are unable to generate traction on loose or slippery terrain, they tend to slip. Slippage wastes energy, which lead to a loss of control or becoming stuck e.g. An automatic 4-wheel drive in mud or snow. For instance, legged vehicles are preferred in the logging industry, as the terrain is too challenging for wheeled vehicles to navigate. Tracked vehicles slip less often than wheeled vehicles, because their contact area with the ground is larger. However, they tend to have larger turning radii than wheeled vehicles, hence are limited in efficiency and more mechanically complex.
— Obstacle navigation:
Mieczyslaw Bekker implied a log-normal distribution of irregularities in natural terrains, meaning smaller obstacles are far more common than larger ones. Therefore, locomotion in natural terrains at all size scales have to face the challenge of obstacle navigation. Though each has its attendant challenges, the primary objective of obstacle navigation on land is to navigate around and traverse over obstacles.
— Going around = Michael LaBarbera compared the turning radii of walking and wheelchair-using humans, which illustrated the poor manoeuvrability of wheels. Jared Diamond asserted that most biological examples of rolling are found in wide open, hard packed terrain, such as dung beetles and tumbleweeds.
— Going over = Wheels have difficulties dealing with vertical obstacles, especially those on the same same as the wheel itself, as they are unable to climb vertical obstacles taller than about 40% of the wheel height. Therefore, rough terrain requires wheels to have a larger diameter. Without articulation, wheeled vehicles can stick on top of an obstacle, with the obstacle lodged between its wheels, preventing them from contacting the ground. Whereas, limbs are equipped to deal with uneven terrain, making them useful for climbing.
If the wheels are unarticulated, the vehicle’s body will tilt as they climb such obstacles. If the vehicle’s centre of mass shifts outside of the wheelbase or axle track, it causes static instability and the vehicle tends to tip over. If the vehicle is moving at speed, it causes dynamic instability, meaning an obstacle smaller than its static stability limit, or excessive acceleration or tight turning can tip the vehicle over. Therefore, wheeled vehicles have suspension systems to mitigate the tendency of overturning. However, unlike fully articulated limbs, suspension systems are unable to help the vehicle recover from an overturned position.
— Versatility:
Animals that use their limbs for locomotion over terrain also use them for other purposes, such as grasping, manipulation, climbing, branch-swinging, swimming, digging, jumping, throwing, kicking, and grooming. An unarticulated wheeled-vehicle lacks the versatility to cope with different locomotive challenges unfortunately.
(c) Fossorial = Underground
https://en.wikipedia.org/wiki/Fossorial
— Subterranean = Some animals move through solids such as soil by burrowing using peristalsis, for instance, earthworms. Other animals, such as the golden mole, marsupial mole, and the pink fairy armadillo, move through loose solids such as sand, more rapidly, as if they are “swimming” through the loose substrate. Burrowing animals include moles, ground squirrels, naked mole-rats, tilefish and the mole crickets.
There is prehistoric evidence that the physical adaption of fossoriality is widespread among many prehistoric phyla and taxa, such as bacteria and early eukaryotes. A 2018 study uncovered further evidence of fossoriality evolving independently multiple times, even within a single family. A 1987 study theorised the arthropods’ colonisation of land in the late Ordovician period (over 440 million years ago) coincided with the appearance of fossorial animals. A 2015 study noted the earliest burrowers include Eocaecilla and possibly Dinilysia. Estimated to be 251 million years old, the oldest example of burrowing in synapsids, which its lineage includes modern mammals and their ancestors, is a Cynodont, Thrinaxdon liorhinus, found in the Karoo of South Africa. A 2003 study showed this adaption may have occurred due to dramatic mass extinctions in the Permian period.
In 1903, H.W. Shimer described 6 major external modifications shared in all mammalian burrowing species:
— Fusiform = A spindle-shaped body tapering at both ends, adapted for the dense subsurface environment.
— Lesser developed or missing eyesight, considering subsurface darkness
— Small or missing external ears = Reduces naturally occurring friction during burrowing.
— Short and stout limbs = Swiftness or speed of movement is considered less important than digging strength.
— Broad and stout forelimbs (manus) = This includes long claws, which are designed to loosen the burrowing material for the hind feet to disperse in the back. In 2005, Jorge Cubo argued the skull is the main tool during excavation, but the forelimbs are mostly active for digging and the hind-limbs for used for stability.
— Short or missing tail = Little to no locomotor activity or burrowing use to most fossorial mammals.
Other important physical features include a subsurface adjusted skeleton:
— A triangularly shaped skull
— A prenasal ossicle
— Chisel-shaped teeth
— Effectively fused and short lumbar vertebrae
— Well-developed sternum
— Strong forelimbs
— Weaker hind limb bones
Because their dark subsurface environment lacks light, fossorial creatures develop certain physical, sensory traits to help them communicate and navigate. Since sound travels slower in the air and faster through solid earth, fossorial animals create seismic (percussive) waves on a small scale to give them an advantage. e.g. The Cape mole rat (Georychus capensis) sends conspecific signals through drumming behaviour to send messages to its kin. The Namib Desert golden mole (Eremitalpa grant namibensis) use their hypertrophied malleus to detect termite colonies and similar prey underground, as well as low-frequency signals. In 2001, Mason theorised bone conduction is the reason for the actual transmission of these seismic inputs, captured by the auditory system. It is suggested the signals travel through many routes to the inner ear whenever vibrations are applied to the skull.
Due to the seasonal lack of soft, succulent herbage and other sources of nutrition, many fossorial and sub-fossorial mammals living in temperate zones with partially frozen grounds tend to hibernate. Shimer suggested species that failed to find food and protection from predators aboveground likely adopted the fossorial lifestyle. In 2007, E. Nevo proposed that harsh aboveground climates may have lead to the emergence of fossorial lifestyles. This transition to an underground lifestyle also entail changes in metabolism and energetics, often in a weight-dependent manner. Sub-fossorial species weighing more than 80 grams (2.8 oz) theoretically have lower basal rates than those weighing lower than 60 grams (2.1 oz). It is estimated the average fossorial animal’s basal rate ranges between 60% and 90%. In 1979, larger burrowing animals, such as hedgehogs or armadillos, were found to have lower thermal conductance than smaller animals, which is suggested to reduce heat storage in their burrows.
In 2009, Marshall Wilkinson defined “bioturbation” as the alteration of fundamental properties of the soil, including surface geomorphic processes, which he regarded as an important impact on the environment caused by fossorial animals. He evaluated small fossorials, such as ants, termites and earthworms displace massive amounts of soil. This meant the total global rates displaced by these animals are equivalent to the total global rates of tectonic uplift. This also directly impacts on soil's composition, structure, and growing vegetation, which causes differential feeding, harvesting, caching and soil disturbances considering the large diversity of fossorial (herbivorous) species. A 1994 study calculated the net effect composed of an alteration of the composition of plant species and increased plant diversity impacts on standing crops, and the homogeneity of the crops. Mounds and bare soils containing burrowing animals impacts the nitrogen cycle in the affected soil by increasing levels of NH4+ and NO3— , as well as increasing nitrification potential and microbial NO3— consumption than in vegetated soils. A 2003 study by Canals proposed the removal of the covering primary mechanism for this occurrence.
(d) Aerial = In the air
https://en.wikipedia.org/wiki/Flying_and_gliding_animals
(i) Unpowered
This mode of locomotion requires the animal to use aerodynamic forces exerted on the body due to wind or falling through the air. These animals often start from a raised location, converting that potential energy into kinetic energy. Aerodynamic forces are then used to control trajectory and angle of descent. Energy is continually being wasted due to drag without being replaced, thus limiting its range and duration.
— Falling = The animal’s altitude decreases under the force of gravity, without using any adaptations to increase drag or generate lift.
— Parachuting = Animals fall at an angle greater than 45o from the horizontal with adaptations to increase drag forces. Wind may carry smaller animals upwards and towards a certain direction. Some gliding animals use their gliding membranes for drag rather than lift to ensure a safer descent.
— Gliding = Animals fall at an angle less than 45o from the horizontal with lift from adapted aerofoil membranes. This slows down the rate of falling relative to the horizontal, in addition to streamlining that decreases drag forces for aerofoil efficiency and maneuverability in air. Gliding animals have a lower aspect ratio (wing length/breadth) than true flyers.
An ecological advantage of gliding is its energy efficiency when travelling between trees. Critics argue that many gliding animals eat low energy foods such as leaves restricting their movement to gliding, whereas flying animals eat more high energy foods such as fruits, nectars, and insects. In contrast to flight, the evolution of gliding has occurred independently on numerous occasions, at least a dozen times among extant vertebrates. Nonetheless, these groups have not radiated as much as have groups of flying animals. There is an uneven distribution of gliding animal populations worldwide as most inhabit Southeast Asian rain forests, whilst a few gliders are found in India or New Guinea and none in Madagascar. Moreover, a variety of gliding vertebrates inhabit Africa, South America such a family of hyoids (flying frogs), and forests of northern Asia and North America such as gliding squirrels. Such disparities can be explained by various factors. The dominant canopy tress (usually dipterocarps) in Southeast Asian forests are taller than the canopy trees of the other forests. This higher start gives a competitive advantage to animals leading to further glides and farther travel, which increases the efficiency of searching for prey. Furthermore, there may be smaller populations of insect and small vertebrate prey for carnivorous animals (such as lizards) in Asian forests. Whereas in Australia, many mammals (and all mammalian gliders) possess prehensile tails to a certain extent.
When an animal free-falls without any aerodynamic forces, gravity provides its acceleration, which results in increasing velocity during descent. Whereas, when an animal parachutes, its body’s aerodynamic forces counteracts opposing forces or gravity. Objects moving through air experiences a drag force proportional to both the surface area and velocity squared, which partially cancels out the gravitational force, therefore slowing down the animal’s descent to a safer velocity. When the drag force’s angle is relative to the vertical, the animal’s trajectory gradually leans towards the horizontal, covering distance both horizontally and vertically. Tiny adjustments are required to change direction by turning or other maneuvers, which allows parachuting animals to move through a high position on 1 tree to a low position on another adjacent tree.
When an animal glides, their lift is proportional to the velocity squared. They typically leap or fall from higher locations such as tree tops, which involves increases in gravitational acceleration, aerodynamic forces hence velocity. This leads to animals gliding at shallower angles relative to parachuting animals, which leads to greater horizontal coverage in the same decreases of altitude, and reach for trees a greater distance away.
(ii) Powered flight
This mode of locomotion requires the animal to use its own muscular power to generate aerodynamic forces to climb or to maintain steady, level flight. This allows the animal to produce thrust, thence lift. Nevertheless, the animal may ascend without the aid of rising air.
Flying and gliding animals (volant animals) have many separate evolutionary lineages with no single ancestor. The evolution of flight occurred at least 4 times in insects, pterosaurs, birds, and birds. There are 3 extant groups of powered flyers, each containing a large number of species, which emphasises the successful strategy of flight as a form of evolutionary locomotion. Bats have the most species, more than any other mammal, accounting about 20% of all mammalian species. Birds have the most species amongst terrestrial vertebrates. However, insects have more species than all other animal groups combined.
Many scientists proposed theories regarding the evolution of flight in the animal kingdom. Since most flying animals were small in size and had a low mass (both of which increase the surface-area-to-mass ratio), they fossilised infrequently and poorly compared to their larger, heavier-boned terrestrial inhabitants. Instead, the fossils of flying animals were confined to exceptional fossil deposits formed under specific circumstances, which may lead to poor fossil records and a lack of transitional forms. Moreover, as fossils don’t preserve behaviour or muscle, it’s difficult whether the fossilised animals was a poor flyer or a great glider.
Historians estimated insects were the first organisms evolved to fly approximately 350 million years ago. However, this is debate regarding the developmental origins of insect wings and its actual evolutionary purpose prior to true flight. Theories on the purpose of wings ranged from its initial usage to catch the wind to help small insects living on the water surface, to parachuting, then gliding, then flight for originally arboreal insects.
Approximately 228 228 million years ago, pterosaurs were the next to evolve flight, which were close relatives of the dinosaurs. They had gigantic body sizes, and the last of them were thought to be the largest flying animals ever to inhabit the Earth, with wingspans of over 9.1 m (30 ft). However, they spanned a large range of sizes, down to 250 mm (10 in) wingspan in Nemicolopterus.
Birds were known to evolve from small theropod dinosaurs and its numerous bird-like forms which didn’t survive he mass extinction at the end of the Cretaceous, leading to extensive fossil record. 2 years after Darwin’s publication of On The Origin of Species, archeologists remarkably discovered the fossil remains of the Archaeopteryx, which shares both reptilian and avian anatomy. Nonetheless, there is a contentious divide amongst scientists regarding the ecology of this transition. Some scientists either support "trees down" origin (in which an arboreal ancestor evolved gliding, then flight) or a "ground up" origin (in which a fast-running terrestrial ancestor used wings for a speed boost and to help catch prey).
Approximately 60 million years ago, bats evolved most recently and likely from a fluttering ancestor (according to Matt Kaplan), though their poor further detailed study is hindered by a poor fossil record.
Some large birds including the extinct pterosaurs were known to be specialised in soaring. Although it was high energy expenditure, soaring provides an advantage because it reduces wing loading (i.e. Large wing areas relative to their weight), hence maximises lift.
Flying animals flap their wings relative to their body to generate both lift and thrust. This raises the difficulty of understanding flight in flying organisms because it involves varying speeds, angles, orientations, areas, and flow patterns over the wings.
When a bird or bat flies through the air at constant speed, it flaps its wings (usually with some fore-aft movement). During the aerial motion, there is some airflow relative to the animal’s body. Combined with the velocity of its wings, this generates faster airflow moving over the wing. This, in turn, generates a forwards and upwards lift force vector, and a rearwards and upwards drag force vector. The upwards components of these forces counteract gravitational force, keeping the body afloat in the air, while the forward component provides thrust to counteract both the drag from the wing and from the body as a whole.
Due to their miniature size rigid wings, and other anatomical differences, insect flight is mostly affected by turbulence and vortices, which complicates the flight of vertebrates. Most insects create a spiralling leading edge vortex, while some insects use the “fling-and-clap”, or Weis-Fogh mechanism in which the wings clap together above the insect's body and then fling apart. As their wings fling open, this sucks air in to generate a vortex over each wing. This bound vortex then moves across the wing and, in the clap, acts as the starting vortex for the other wing. This increases air circulation and lift, but at the expense of wear and tear on the wings.
The largest known flying animal was formerly though to be Pteranodon, a pterosaur with a wingspan of up to 7.5 m (25 ft). However, a recent discovery of an azhdarchid pterosaur Quetzalcoatlus had a larger wingspan, estimated between 9 and 12 m (30 and 39 ft). The heaviest living flying animals are the
kori bustardand the great bustard with males weighing in at 21 kg (46 lb). The largest currently living animal is the wandering albatross with a wingspan of 3.63 m (11.9 ft). Among living animals flying over land, the
Andean condorand the
marabou storkhave the largest wingspan at 3.2 m (10 ft).
There is no real minimum size for an organism to be airborne. Indeed, there are many bacteria floating in the atmosphere, which constitute part of the aeroplankton. However, a certain size is required to move under one’s own power and not overly affected by the wind. The smallest flying vertebrates are the bee hummingbird and the humblebee bat, both of which weigh less than 2 grams (0.071 oz). They may represent the lower size limit for endotherm flight.
The fastest of all known flying animals is the peregrine falcon, which when diving travels at 300 km/hr (190 mph) or faster. The fastest animal in flapping horizontal flight may be the Mexican free-tailed bat, thought to attain about 160 km/hr (99 mph) based on ground speed by an aircraft tracking device. However that measurement does not separate any contribution from wind speed, so the observations could be caused by strong tailwinds.
Although most flying animals travel forward to stay afloat but some remain in the same position, known as hovering, either either by rapidly flapping the wings or by using thermals. For instance, hummingbirds, hoverflies, and dragonflies, and some birds of prey, respectively. The slowest flying non-hovering bird recorded is the American woodcock, at 8 km/hr (5.0 mph).
There were records of a large vulture called Rüppell’s vulture Gyps rueppelli being sucked into a jet engine 11,550 metres (37,890 ft) above Côte d’Ivoire in West Africa. The animal that flies highest most regularly is the bar-headed goose Anser indicus, which migrates directly over the Himalayas between its nesting grounds in Tibet and its winter quarters in India. Occasionally, they fly well above the peak of Mount Everest at 8,848 metres (29,029 ft).
(iii) Externally powered
This mode of locomotion aren’t powered by muscle, but instead by external aerodynamic sources of energy such as wind and rising thermals.
— Soaring = Animals glide in rising or moving air requiring specific physiological and morphological adaptations in order to sustain flight without flapping their wings. The sources of rising air include thermals, ridge lifts or other meteorological features. Under suitable conditions, soaring leads to increases in altitudes without expending energy, however larger wingspans are required to soar efficiently.
— Ballooning = Air from the aerodynamic effect on long strands of silk in the wind carry the animal up off the ground and into the air. Arthropods like small or young spiders secrete a special light-weight gossamer silk to balloon in the wind, hence travel large distances at high altitude.
In reality, many species utilises multiple modes of aerobic locomotion at various times. For example, a hawk lifts using powerful flight, then soars on thermals, before descending via free-fall to catch its prey.
Passive Locomotion:
This type of mobility is dependent on the environment for animal transportation.
The Portuguese man o’ war (Physalia physalia) lives at the surface of the ocean. While most of its body is submerged, its gas-filled bladder, or pneumatophore (sail) remains at the surface. Instead of self-propulsion, this hydrozoan uses a combination of winds, currents and tides to move along the ocean surface by its sail. Its sail is equipped with a siphon, so it can be deflated in the event of a surface attack. This allows the organism to briefly submerge.
The wheel spider (Carparachne aureoflava) is a huntsman spider found in the Namib Desert of Southern Africa. It flips onto its side and cartwheels down sand dunes at speeds of up to 44 turns per second to escape parasitic pompilid wasps. On sloped dunes, this spider rolls up to 1 metre per second.
Some spider species, or spiderling after hatching, climb as high as it can, by standing on its raised legs with its abdomen pointed upwards (“tiptoeing”). They then release several silk threads from its spinnerets into the air to form a triangle-shaped parachute to carry its body on updrafts of winds. In windless conditions, Earth’s static electric field may also lift the spider’s body.
The larva of Cicindela dorsalis, the eastern beach tiger beetle, is known for its ability to leap into the air, loop its body into a rotating wheel and roll along the sand at a high speed using wind to propel itself. With an adequately strong wind, the larva can cover up to 60 metres (200 ft) in this manner. This locomotion may have evolved to help the larva escape predators such as the thynnid wasp Methocha. Members of the largest subfamily of cuckoo wasps, Chrysidinae, are kleptoparasites that lay their eggs in host nests. Their larvae consume the host egg or larva while it is still young. Chrysidines have flattened or concave lower abdomens that allow them to curl into a defensive ball when attacked by a potential host, a process known as “conglobation”. When they are expelled from the nest without injury to search for a less hostile host, their hard chitin protects them in this position.
Fleas are found to jump vertically up to 18 cm and horizontally up to 33 cm, albeit uncontrollably. Therefore they always jump in the same direction, with little variation in the trajectory between individual jumps.
Although stomatopods typically display the standard locomotion types as seen in true shrimps and lobsters, Nannosquilla decemspinosa has been seen to flip itself into a crude wheel. At low tides, they are often stranded by its short rear legs, which are sufficient for locomotion when the body is supported by water, but not on dry land. To attempt a roll towards the next tide pool, the mantis shrimp then performs a forward flip. They have been observed to roll repeatedly for 2 m (6.6 ft), but they typically travel less than 1 m (3.3 ft).
(v) Animal Transport:
The term “animal transport” is defined as change in an animal’s location after an attachment, or residence on another animal or moving structure.
They are a family (Echeneidae) of ray-finned fish that have a distinctive first dorsal fins, which look like a modified oval, sucker-like organ with slat-like structures. These structures open and close to create suction that firmly hold against the skin of larger marine animals. By sliding backward, the remora can increase the suction. On the other hand, by swimming forward, they can decrease suction to release itself. They swim well on their own, with a sinuous, or curved, motion, with its fully formed disc reaching about 3 cm (1.2 in) when attaching to other animals. Because they lack a swim bladder, the remora’s lower jaw projects beyond the upper jaw. They commonly attach to sharks, manta rays, whales, turtles, and dugongs. Smaller remoras also fasten onto fish such as tuna and swordfish, while other small remoras travel in the mouths or gills of large manta rays, ocean sunfish, swordfish, and sailfish. Using the host as transport and protection, this benefits the remora as they feed on materials dropped by the host.
When a male anglerfish finds its opposite sex, he bites into her skin, and releases an enzyme that digests the skin of his mouth and her body, fusing the pair down to the blood-vessel level. The male then receives nutrients from the female host via their shared circulatory system, and provides sperm to the female in return. After fusing, males increase in volume and size relative to free-living male anglerfish. As long as the female lives, male anglerfish live and remain reproductively functional, as well as participate in multiple spawnings. This sexual dimorphism ensures the female anglerfish has a mate immediately available upon spawn readiness. Studies found up to 8 males can be incorporated into a single individual female, though some taxa appear to have a 1 male per female rule.
— Parasites:
Many parasites are transported by their hosts. e.g. Endoparasites such as tapeworms live in the alimentary tracts of other animals, and they distribute their eggs depending on the host’s ability to move. Ectoparasites such as fleas can move around on the body of their host, but the host’s locomotion transports them for much longer distances. Some ectoparasites such as lice can opportunistically hitch a ride on a fly (phoresis) and attempt to find a new host.
Changes between environment media:
Some animals move between different media, e.g., from aquatic to aerial, which requires different modes of locomotion in the different media, hence a distinct transitional locomotor behaviour. Semi-aquatic animals spend part of their life cycle or, in general, anatomy underwater. They represent the major taxons of mammals (e.g., beaver, otter, polar bear), birds (e.g., penguins, ducks), reptiles (e.g., anaconda, bog turtle, marine iguana) and amphibians (e.g., salamanders, frogs, newts).
(a) Fish
- Walking fish occasionally swim freely or “walk” along the ocean or river floor, but not on land (e.g., Flying gurnard, and batfishes of the family Ogcocephalidae).
- Amphibious fish can leave the water for extended periods of time, which demonstrate a range of terrestrial locomotory modes, such as lateral undulation, tripod-like walking (using paired fins and tail), and jumping.
- Many of these locomotory modes incorporate multiple combinations of pectoral, pelvic and tail fin movements. Examples include eels, mudskippers and the walking catfish.
- Flying fish propel themselves to leap out of water into air, where their long, wing-like fins enable gliding flight for considerable distances (around 50m and up to 400 m (1,300 ft) using updrafts t the leading edge of waves) above the water's surface. This serves as a natural defence mechanism to evade predators. They can travel at speeds of more than 70 km/h (43 mph) and achieve a maximum altitude is 6 m (20 ft) above the surface of the sea, potentially landing on ships’ decks.
(b) Marine Mammals
As they swim, several marine mammals such as dolphins, porpoises and pinnipeds, frequently leap above the water surface whilst they maintain horizontal locomotion. As they travel, dolphins and porpoises jump to conserve energy due to the air having less friction, known as “porpoising”. They porpoise to orient, display socially, fight, communicate non-verbally, entertain and attempt to dislodge parasites. Pinnipids have been observed to demonstrate both “high” and “low” porpoising. “High porpoising” often occurs near (within 100 m) the shore, followed by minor course changes. This helps seals get their bearings on beaching or rafting sites. Whereas, “low porpoising” often occurs relatively far (more than 100 m) from shore, and often aborted in favour of anti-predator movements. This allows seals to maximise sub-surface vigilance and thereby reduce their vulnerability to sharks. Some whales “breach” by raising their ) body vertically out of the water.
(c) Birds
Some semi-aquatic birds demonstrate terrestrial locomotion, surface swimming, underwater swimming and flying (e.g., ducks, swans). Diving birds such as dippers and aulks dive underwater for food, while other birds (e.g. ratites) lost the primary locomotion of flight. The largest flightless 2-legged bird, called an ostrich, is known to reach speeds over 70 km/h (43 mph), and maintain a steady speed of 50 km/h (31 mph), when pursued by a predator. April Holladay observed ostriches swimming but she hasn’t measured whether they swim as fast as their running. Penguins either waddle on their feet or slide on their bellies across the snow, known as “tobagganing", to conserve energy while they move rapidly. If they have to move more quickly or cross steep or rocky terrain, they jump with both feet together. To step onto land, penguins occasionally propel themselves upwards at a great speed to leap out the water.
Changes during the life-cycle:
Some animals change their mode of locomotion during their life cycle. For example, barnacles are exclusively marine and tend to live in shallow and tidal waters. They have 2 nektonic (active swimming) larval stages, but as adults, they are sessile (non-motile) suspension feeders. Adult barnacles are often found attached to moving objects such as whales and ships, and are thereby transported (passive locomotion) around the oceans.
Function:
Animals move for a variety of reasons, such as to find food, a mate, a suitable microhabitat, or to escape predators.
— Food procurement:
To procure food, animals use different terrestrial methods such as ambush predation, social predation, and grazing, as well as aquatic methods such as filter feeding, grazing, ram feeding, suction feeding, protrusion and pivot feeding. Other obscure methods include parasitism and parasitoidism.
https://physicstoday.scitation.org/doi/full/10.1063/PT.3.3691
How did the physics of animal locomotion emerge?
Richard Feynmann once said, “What I cannot create, I do not understand.” Despite researchers’ engineering abilities, failure to meet Feynmann’s standard is due to the difficulty of understanding and modelling the emergence of movement from the physical and physiological systems of organisms. Humans experience difficulty replicating the systems that help animals move around with ease and agility, which explains why we haven’t successfully emulated the motility witnessed in nature or derived the animal’s behaviour. Examples range from moths flitting between flowers on a moonlit night to cockroaches scurrying underfoot, which are dynamic systems. In the 1944 book “What is Life?”, Erwin Schrödinger discussed the limits of reductionism in explicating the physics of life and recognised that new principles need to arise from examinations of life at the macro scale.
— Discuss the science of movement, neuromechanics.
All animals, as well as plants, fungi and prokaryotes, demonstrate capabilities of moving, which evolved from diverse strategies to generate stable and manoeuvrable dynamics to handle terrain that is compliant, flowing, slippery or uncertain. We know animal movements requires the acquisition, processes and actions on information delivered by neurons, muscles, the body, and the external environment.
Neural feedback includes reflexes akin to the response that activate when stretch receptors in muscles detect the tapping of one of the knee tendons, for example. Such feedback encompasses both visual and vestibular (inner ear) signals and other internal and external sensory methods. These signals are processed by afferent sensory neurons, which in turn changes the brain’s activation of muscles. However, the forces muscles produce are complex because they are also state dependent. This means, as muscle strain changes through joint extension, force also changes, regardless of neural activation changes. This state dependence is due to the muscle being a complex object composed of a fluid-filled, hierarchical tissue containing millions of microscopic motor proteins arranged into an active lattice.
Neuromechanics considers how movement arises through the interplay of multiple physiological systems and their interactions with the environment around the animal. Understanding how those systems control movement remains elusive in part because no one animal can serve to test all neuromechanical hypotheses.
— Discuss insect flight and unsteady aerodynamics
Notice that as the moth hovers, their wings are at extremely steep angles of attack, like in most insect and hummingbird flight. Higher angles theoretically would lead to turbulence and stall as the flow separates from the wings. So how does an insect manage to stay aloft? Researchers discovered that there is separation of the insect’s wings due to the unsteady flow over them, then reattachment of same wings to generate regular coherent structures (i.e. vortices bound to the wing) that help the insect produce lift. This mechanism was first discovered by zoologist Torkel Weis-Fogh in the 1970s when he was examining the chalcid wasp (Encarsia formosa). He found that the insect’s wings clap together before separating and flinging outward at the end of its upstroke, which allowed air to refill the vacated space. Mathematician James Lighthill characterised the mechanics behind the clap-and-fling action by establishing the idea of equal and opposite circulations on each wing during the fling as the 2 clapped wings separate. Because the air flows over them is directed downward toward the surface for the wings to reattach and stabilise the vortex, trapping the circulations generates the added lift. This redirection of air flow effectively sucks wing normal to its surface, hence generate lift and drag.
Most flapping animals don’t clap their wings together fully, which contrasts Weis-Fogh’s and Lighthill’s finding of the specific clap-and-fling behaviour. In the late 1990s and early 2000s, more general mechanisms were identified for insect flight.
As the wing moves, the flow around it revolves produce a bound vortex on its leading edge and with smoke visualisation. Those leading-edge vortices (LEVs) enhance lift via a clap-and-fling mechanism described by Weis & Fogh, which have since been demonstrated to be ubiquitous in biological systems. This reinforces its importance in flight of small birds, bats, and spinning helicopter seeds of maples. Other unsteady aerodynamic mechanisms are suggested to increase lift and modulate flight forces. During flight, there is interaction between the fly’s wing and the vortex wake shed from the previous wing stroke. Energy from those interactions can be recaptured to illustrate the mechanisms involved in storing and return energy to the environment. However, when the animal encounters air that is already disrupted, how LEVs persist or are modified remains unclear. So far, most studies on the mechanisms of flight have been performed in still or steadily flowing air. One question remains unanswered: “If the moth and other flapping insects and birds rely on binding vortices to their wings, how do they produce, stabilise, and modulate those vortices in environments where the fluid is already unsteady or even fully turbulent?
— Describe the simple models and important insights
Emergent behaviours are complex patterns resulting from interactions of simple components that don’t display the emergent patterns of the whole. It is challenging to understand the emergent behaviour of physiological systems or whole organisms as the system components are complex themselves. Heterogeneous structures consist of neurons, muscles, limbs, and the matter surrounding the animal. However, many low-dimensional dynamics models contain a few degrees of freedom to describe gaits and movement strategies. One example template model described the model of animals running, bouncing up and down like a spring-loaded inverted pendulum.
A dynamics model in the lateral plane shows the total reaction force on the 3 legs of a cockroach’s tripod acting like a simple conservative spring force. This would cause the insect to bounce sideways and rotate in plane. With every animal step, energy is conserved by SLIP and lateral dynamics. Due to a lack of a mechanism to dissipate energy generated by means of perturbations (e.g. a small change in external force due to a bump in terrain), there is no stability in an energy-conserving dynamic system. Simple lateral templates can provide stable motion due to the discontinuity in the animal’s gait (i.e. one limb or set of limbs picks up and the next set touches down). At this point, the direction of the spring force suddenly changes to stabilise the motion ensuring a sufficient transition. Robert Full and Simon Sponberg found animals, well as robots, demonstrate dynamic stability through maintenance of their steady, alternating gait mechanics. One finding included activation patterns in cockroach leg muscles remained the same, suggesting stability in their mechanical motion. Unless perturbations become substantial forcing the cockroach to actively modify its behaviour. Moreover, legged robots are able to run stably over a suitably scaled version of the same rough terrain through simple maintenance of an alternating tripod gait with or without no external sensors. Not even size-adjusted leg stiffness can reduce the robot’s peak speed relative to animals. However, the simple template models aren’t a panacea for the complexity of living systems, but rather a starting point. Unfortunately, the model’s simplicity fails to capture specifics that contribute to animal locomotion. Damping is critical for shock absorption in most biological movement, while robust stability requires neural feedback and movement control is dependent on the limbs’ interaction with their surrounding environment. Scientists are at the elementary stage of understanding the physics behind the interactions between a moving, deformable body and a flexible rough (high-friction) terrain. Template models do provide insight into the missing components that need to be embedded into more complex models, nonetheless. This requires understanding of the scales at which new dynamical features emerge.
— Describe the quantitative patterns of behaviours
One of the most significant constraints on linking physics to locomotion was the challenge of capturing complex movements with sufficient scope and precision to extract quantitative patterns. Along with cultural and technological limitations, this contributed to physicists’ reluctance to handle problems in macroscopic or even mesoscopic living systems compared to those at the molecular and cellular level. Recent technological advances such as high-speed imaging, machine vision (automated inspection), motion capture, and rapid prototyping have enhanced scientists’ understanding of movement, increasing the feasibility of collecting 1000s of steps, wing strokes, and other motions in a single experiment. However quantification needs to be integrated with statistical physics and biophysics to identify relatively simple patterns and low-dimensional structures present in animal movement. 1 study applied 4 degrees of freedom to capture 95% of the movements of the small roundworm Caenorhabditis elegans to deconstruct its movements, which lead to the discovery of 2 of the dimensions determining the phase of the oscillatory body wave.
— Describe how feedback dynamics change
The behaviour of many living and engineered dynamic systems associates with feedback in some way. When the output of a dynamic process changes the input into that process, feedback occurs in the system. This would lead to profound effects on both the qualitative and quantitative dynamics of movement, which emphasises its ubiquity in living systems. Feedback acquires information about the effects of our movements and compares that information with a reference signal. An example includes sensing the position of my own arm relative to my brain’s subconscious intention to position it. Then my nervous system detects exogenous cues. For instance, a moth relies on exogenous cues to track a flower. Its visual system detects information regarding the difference between the motion of the flower and the moth’s own movement, which the moth aims to vanish.
Moths were found to slow their processing to increase sensitivity to an extent, as long as they accurately tracked flower movements below about 2 Hz, which most flower movements oscillate in windy conditions. This suggested moths evolved to match their neuromechanics to the dynamics of their preferred flowers.
— Discuss the multiscale physics of living assemblages
Multiscale networks are an organised lattice of brains, muscles, and other physiological systems, which can lead to unexpected emergent dynamics. In particular, active network subunits are capable producing forces on their environment. Consider the structure of a muscle, it produces diffraction patterns upon exposure to narrow beams of high-energy x-rays. Organised into a regular lattice, the protein filaments that underlie contraction are Actin and Myosin. These lattices are arranged into sarcomeres, with each muscle cell containing at least 1 sarcomere or up to several 100 sarcomeres.
Changes in the filamentary lattice space can significantly change the macroscopic behaviour of muscle. In moths, a decrease in temperature by 10 degrees C locks up the lattice in its main flight muscles, causing them to acts like a motor when warm to store and return energy like a spring when cool.
When organisms behave in aggregations, they perform collection actions outside the confines of a single living organism. Examples include flocking and schooling, which have interesting energetic and ecological consequences, as well as manifest a diverse range of emergent properties and behaviours. For example, colonies of ants span gaps and survive floods by forming rafts and bridges. The collective action of honeybees controls the fluid dynamics of the hive, enhancing their home’s ventilation.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4313093/
In 2015, Fukuoka, Habu & Fukui used simulations of quadrupedal locomotion to discover a rule for generating typical quadrupedal gaits. Gaits previously not programmed such as diagonal/lateral sequence walks, left/right-lead canters, and left/right-lead transverse gallops emerged due CPGs receiving leg loading feedback to produce a default trot. Furthermore, all of these gaits transitioned to speed, which matched previously reported observations in animals. They hypothesised that various gaits derive from a trot thanks to posture control through leg loading feedback. They classified the body tilt on the 2 support legs of each diagonal pair during trotting into 3 types according to their speed: Level, Tilted Up and Tilted Down. After analysing the load difference between the 2 legs led to the phase difference between their CPGs via the loading feedbacks, 9 gaits were yield including the aforementioned.
https://royalsocietypublishing.org/doi/10.1098/rspb.2006.3489
A 2006 study by Reilly et al. analysed lumbering locomotor behaviours of tuataras and salamanders and theorised these terrestrial creatures demonstrated the earliest traits of quadrupedal locomotion. Both animals show identical walking (out-of-phase) and running (in-phase) patterns of external mechanical energy fluctuations of the centre-of-mass, which are reminiscent of fast moving (cursorial) animals. These mechanics share features with tetrapods since quadrupedal locomotion emerged over 400 million years ago. Like cursorial animals, tuataras and salamanders demonstrate pendular effectiveness in order to save external mechanical energy. However, unlike cursorial animals, tuataras and salamanders demonstrate only diagonal couplet gaits and indifferent transitions from walking to to running mechanics with little change in total mechanical energy rather than change footfall patterns and mechanics with speed. Therefore, Reilly et al. hypothesised that speed is unrelated to the switch from walking to running but the advantage of walking over running remains unclear. Unlike cursorial animals, primitive tetrapods demonstrate larger relative centre-of-mass displacements and their potential energy drives their total mechanical energy. This lead them to conclude that an association between large vertical displacements and lumbering locomotion in primitive tetrapods is responsible for the preclusion to increase the tetrapod’s speed.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3424743/
There is experimental evidence for the existence of biomechanical constraints, which simplify the conundrum of multi-segment movement control. A 2012 study hypothesised that a set of basic temporal components or activation patterns are responsible for controlling movements. They may be shared by several different muscles, which reflect its global kinematic and kinetic goals. Recent studies on human locomotion showed a combination of basic patterns, each one timed at a different phase of the gait cycle, account for muscle activity. At different speeds, the same patterns are activated in both walking and running, forwards or backwards, and under different loading conditions.
https://www.nationalgeographic.com/science/phenomena/2016/06/17/our-earliest-example-of-an-animal-moving-on-its-own/
When was the earliest known example of an animal moving on its own?
Discovery of footprints on a dark slab of rock hanging on the edge of the North Atlantic in a remote corner of Newfoundland lead to theories of an unique ocean dweller. It is estimated the footprints were made around 565 million years ago, which suggested this creature may have been the first to use its own muscles to move from one location to another. Archaeologists named them “Ediacarans, which may have had a diverse range of anatomy, from flower-like to mud plops, a palm leaf and a ribbed pancake. Dr Alex Liu recorded photographs of his fossilised discoveries shown below.
It’s theorised millions of years ago at Mistaken Point on the Newfoundland coast, volcanic lava smothered every living creature then froze them in place, before Earth’s slow shift. This lead to the surfacing, sculpting and exposure of the upper rock layer, displaying scores of fern-like, blob-like, pancake-like fossils. Paleobiologists suppose that traces of a suction cup foot may have been used to fasten Ediacarans to rocks or flat surfaces on the ocean bottom, similar to sea anemones. A 2009 study by Alexander Liu and co. suggested Edicarans crawled out of the ocean rather than floated, squirmed, rolled or reached. Their analyses of the primitive proto-steps deduced each step as a series of nesting parentheses. Critics argued these tracks were probably pebbles tossed by waves, but experts supported Liu’s conclusion.
But the question is “Why bother going anywhere? Why move?” Were Ediacarans searching for food? Looking for mates? Escaping a predator? Or were they curious exploring beyond the next hump of sand surrounding them? Life on Earth 565 million years ago was peaceful as it recovered from a deep freeze leaving the sea bottoms devoid of predators. Robert Krulwich proposed a theory that restlessness motivated these ancient pioneers to travel, based on observations of current living animals known to move in greater arcs. However, Moor argues that restlessness doesn’t explain why do humans, as animals, uproot themselves and travel somewhere else. Liu proposed that the inventors of animal locomotion seek secure shelter i.e. a clean, flat surface to cling to, and comfort rather than adventure. Philosophically speaking, no place stays safe forever, not even Earth. At a certain point in time, either by restlessness or desperation, any creature has to continue moving to survive given the challenges nature throws at them.
https://www.quantamagazine.org/why-did-life-move-to-land-for-the-view-20170307/
Another study attempted to answer the question regarding the feasible, plausible and logical reasons life moved from the sea to the land. Evolutionary biologists inferred life on Earth started underwater. When life transitioned from the water to land, anatomical tradeoffs had to be made to adapt to new terrestrial environments, including fins for limbs, and gills for lungs. But this is only part of the story. Malcolm MacIver’s study claimed that these organisms gained the ability to attain new information, which he regarded as more precious than oxygenated air. Animals had improved visual acuity and visual range as their eyes could see longer distances than in water. This provided an “informational zip line” to alert the ancient terrestrial animals of the presence to abundant food sources near the shore. This zip line may have naturally selected animals to evolve rudimentary limbs in order to make their first brief forays onto land. This implicated the emergence of more advanced cognition and complex planning.
MacIver articulated his argument based on the South Americanblack ghost knifefish, a electric fish that generates electrical currents in the water to sense its environment and hunt at night. To study its exotic sensing abilities and its unusually agile movement, he constructed a robotic version of the knifefish. After MacIver compared the volume of space in which the knifefish can potentially detect water fleas with that of a fish that mainly relied on vision to hunt the same prey, he found some similarities, which he considered intriguing. This observation defied expectations of the knifefish having a smaller sensory volume for prey compared to that of a vision-centric fish as substantial amounts of energy was required to generate electricity for perception of its surroundings. Upon realisation, the critical factor that accounted for the unexpectedly small visual sensory space was the absorption and scattering of light by the water. In fresh shallow water, the “attenuation length” (i.e. Distance that light can travel before it is scattered or absorbed) ranged from 10 cm to 2 m. Whereas in air, the attenuation length ranged from 25 to 100 km, depending on the amount of moisture in the air. Therefore MacIver concluded that an increase in eye size didn’t provide much evolutionary benefits to aquatic animals. Because eyes have high energy requirements and expenditure evolutionarily due to their photoreceptors and neurons of the visual pathway to the brain requiring substantial amounts of oxygen and nutrients to maintain its function. Justification for extra energy to increase eye size would be required if it theoretically advanced vision evolutionarily.
Larger eye sizes in the air, however, have a proportionately longer visual range. This lead to the formation of MacIver’s hypothesis that increase in eye size was a sign of ancient creatures transitioning from the water to land. One fossil observed to have both lungs and gills was a 375 million year old Tiktaalik roseae, discovered by evolutionary biologist Neil Shubin.
MacIver and Schmitz compared the eye socket sizes of 59 early tetrapod skulls by measuring both the eye orbit and the length of the skull. They discovered a significant increase in eye size, by a factor of 3, during the transitional period. Before the transition, the average eye socket size was 13 mm, and after the transition, this increased to 36 mm. Creatures that transitioned from water to land and then back to the water again like the Mexican cave fish Astyanax mexicanus, had their mean orbit size shrunk back to 14 mm, close to its original underwater eye socket size. However, these results were evaluated based on the assumption that animals were fully terrestrial after the eye socket increase occurred. Nevertheless, the shift occurred before the water-to-land transition was already complete prior to the development of rudimentary digits on their fishlike appendages. So one would ask “How could a terrestrial lifestyle drive the gradual increase in eye socket size?
Sven Popping proposed that early tetrapods probably hunted like crocodiles, waiting for the prey to approach them with their eyes peering out of the water. MacIver suggested that “hunting like a crocodile may have been a gateway drug to terrestriality”, which gave the impression of a large gain in “visual performance from poking eyes above the water to see an unexploited source of prey gradually selected for limbs”. The oldest known creature to walk on foot was the Pederpes finneyae, but it was not a true terrestrial creature. Paleontologists hypothesised that this creature was transitioning from water to land. After accounting for eye anatomy and the surrounding environment, a larger eye increases its visual range by 1 metre (6 to 7 metres) in water, but by 400 metres (200 - 600 m) in air regardless of conditions i.e. Daylight, a moonless night, starlight, clear water and murky water.
In the past decade, scientists such as paleobiologists have adapted various scientific methods from modern comparative biology to fossil record analysis in order to study the relationship between all animals, alive and extinct. This sparked interest in developing experimental models to accurately measure the biomechanics and sensory functions of ancient creatures such as running speed in dinosaurs, and vision of early tetrapods transitioning from water to land. With these methods, one is interested in examining and analysing the generalisability of improved vision during the transitioning periods to other ancient creatures, such as marine reptiles. MacIver pondered that aquatic creatures were reactive to their surroundings due to their limited visual range underwater, meaning reaction times have to be within a few milliseconds (equivalent to a few cycle times of a neuron in the brain) to maximise chances of survival. On the other hand, since terrestrial animals possessed longer visual range, they had more time to assess the situation and strategise, ultimately selecting the best course of action. MacIver theorised that the first land animals began hunting for land-based prey reactively but gradually evolved to develop strategic thinking giving them a competitive advantage when hunting for prey. However, this means, these terrestrial creatures had to contemplate multiple possible outcomes and quickly decide the most suitable outcome. This phenomenon is known as ‘mental time travel,’ or ‘prospective cognition’, which is a cognitive ability all humans possess today. Nevertheless, it is possible other factors may have influenced the development of more advanced cognition, which are unspecified yet. Barbara Finlay pointed out that salmon rely on olfactory pathways to migrate upstream, which suggested the ability to plan ahead didn’t immediately emerge only with improved vision. Other sensory functions such as smell and taste were altered during the critical transition period, as they were originally coupled in the aquatic environment and then segregated in the terrestrial environment. Furthermore, the development of a proper external ear and other features transformed hearing abilities of aquatic creatures that transitioned to the terrestrial environment. This work has implications for the future evolution of human cognition, which would be an evolutionary leap forwards in understanding the history of life on Earth, as well as identify human cognitive blind spots in strategic thinking.
