Terrestrial locomotion has
evolved
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variati ...
as
animal
Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...
s adapted from
aquatic to
terrestrial environments.
Locomotion on land raises different problems than that in water, with reduced
friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction:
*Dry friction is a force that opposes the relative lateral motion of ...
being replaced by the increased effects of
gravity
In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
.
As viewed from
evolutionary taxonomy
Evolutionary taxonomy, evolutionary systematics or Darwinian classification is a branch of biological classification that seeks to classify organisms using a combination of phylogenetic relationship (shared descent), progenitor-descendant relat ...
, there are three basic forms of
animal locomotion in the terrestrial environment:
*
legged – moving by using
appendage
An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body.
In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including ante ...
s
*
limbless locomotion – moving without legs, primarily using the body itself as a propulsive structure.
*
rolling – rotating the body over the substrate
Some
terrain
Terrain or relief (also topographical relief) involves the vertical and horizontal dimensions of land surface. The term bathymetry is used to describe underwater relief, while hypsometry studies terrain relative to sea level. The Latin word ...
s and
terrestrial surfaces permit or demand alternative locomotive styles. A sliding component to locomotion becomes possible on slippery surfaces (such as
ice and
snow
Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes.
It consists of frozen crystalline water throughou ...
), where location is aided by
potential energy
In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors.
Common types of potential energy include the gravitational potenti ...
, or on loose surfaces (such as
sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class ...
or
scree), where friction is low but purchase (traction) is difficult. Humans, especially, have adapted to
sliding over terrestrial
snowpack
Snowpack forms from layers of snow that accumulate in geographic regions and high elevations where the climate includes cold weather for extended periods during the year. Snowpacks are an important water resource that feed streams and rivers as t ...
and terrestrial ice by means of
ice skates,
snow skis, and
toboggans
A toboggan is a simple sled traditionally used by children. It is also a traditional form of transport used by the Innu and Cree of northern Canada.
In modern times, it is used on snow to carry one or more people (often children) down a hill ...
.
Aquatic animals adapted to
polar climate
The polar climate regions are characterized by a lack of warm summers but with varying winters. Every month in a polar climate has an average temperature of less than . Regions with polar climate cover more than 20% of the Earth's area. Most of ...
s, such as
ice seals and
penguins also take advantage of the slipperiness of ice and snow as part of their locomotion repertoire.
Beavers are known to take advantage of a
mud slick known as a "beaver slide" over a short distance when passing from land into a lake or pond. Human locomotion in mud is improved through the use of
cleats. Some snakes use an unusual method of movement known as
sidewinding on sand or loose soil. Animals caught in terrestrial
mudflows are subject to involuntary locomotion; this may be beneficial to the distribution of species with limited locomotive range under their own power. There is less opportunity for
passive locomotion on land than by sea or air, though
parasitism
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...
(
hitchhiking
Hitchhiking (also known as thumbing, autostop or hitching) is a means of transportation that is gained by asking individuals, usually strangers, for a ride in their car or other vehicle. The ride is usually, but not always, free.
Nomads hav ...
) is available toward this end, as in all other
habitat
In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
s.
Many species of
monkeys and
apes use a form of
arboreal locomotion
Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. The habitats pose nu ...
known as
brachiation, with forelimbs as the prime mover. Some elements of the gymnastic sport of
uneven bars resemble brachiation, but most adult humans do not have the upper body strength required to sustain brachiation. Many other species of arboreal animal with tails will incorporate their tails into the locomotion repertoire, if only as a minor component of their
suspensory behaviors.
Locomotion on irregular, steep surfaces require
agility
Agility or nimbleness is an ability to change the body's position quickly and requires the integration of isolated movement skills using a combination of balance, coordination, speed, reflexes, strength, and endurance. More specifically, it i ...
and
dynamic balance known as
sure-footedness.
Mountain goats are famed for navigating vertiginous mountainsides where the least misstep could lead to a fatal
fall.
Many species of animals must sometimes locomote while safely conveying their young. Most often this task is performed by adult females. Some species are specially adapted to conveying their young without occupying their limbs, such as
marsupials
Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a po ...
with their special pouch. In other species, the young are carried on the mother's back, and the offspring have instinctual clinging behaviours. Many species incorporate specialized transportation behaviours as a component of their locomotion repertoire, such as the
dung beetle
Dung beetles are beetles that feed on feces. Some species of dung beetles can bury dung 250 times their own mass in one night.
Many dung beetles, known as ''rollers'', roll dung into round balls, which are used as a food source or breeding cha ...
when rolling a ball of dung, which combines both rolling and limb-based elements.
The remainder of this article focuses on the
anatomical
Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having it ...
and
physiological
Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemica ...
distinctions involving terrestrial locomotion from the
taxonomic perspective.
Legged locomotion
Movement on appendages is the most common form of terrestrial locomotion, it is the basic form of locomotion of two major groups with many terrestrial members, the
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...
s and the
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s. Important aspects of legged locomotion are posture (the way the body is supported by the legs), the number of legs, and the functional structure of the
leg and
foot
The foot ( : feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg mad ...
. There are also many
gait
Gait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed, terrain, the need to maneuver, and energetic efficiency. ...
s, ways of moving the legs to locomote, such as
walking
Walking (also known as ambulation) is one of the main gaits of terrestrial locomotion among legged animals. Walking is typically slower than running and other gaits. Walking is defined by an ' inverted pendulum' gait in which the body vaults ...
,
running
Running is a method of terrestrial locomotion allowing humans and other animals to move rapidly on foot. Running is a type of gait characterized by an aerial phase in which all feet are above the ground (though there are exceptions). This i ...
, or
jumping.
Posture
Appendages can be used for movement in a lot of ways: the posture, the way the body is supported by the legs, is an important aspect. There are three main ways in which vertebrates support themselves with their legs – sprawling, semi-erect, and fully erect. Some animals may use different postures in different circumstances, depending on the posture's mechanical advantages. There is no detectable difference in energetic cost between stances.
The "sprawling" posture is the most primitive, and is the original limb posture from which the others evolved. The upper limbs are typically held horizontally, while the lower limbs are vertical, though upper limb angle may be substantially increased in large animals. The body may drag along the ground, as in salamanders, or may be substantially elevated, as in
monitor lizard
Monitor lizards are lizards in the genus ''Varanus,'' the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, and one species is also found in the Americas as an invasive species. About 80 species are rec ...
s. This posture is typically associated with trotting
gait
Gait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed, terrain, the need to maneuver, and energetic efficiency. ...
s, and the body flexes from side-to-side during movement to increase step length. All limbed
reptile
Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates ( lizards and snakes) and rhynchocephalia ...
s and
salamander
Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All t ...
s use this posture, as does the
platypus
The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or mono ...
and several species of frogs that walk. Unusual examples can be found among
amphibious fish
Amphibious fish are fish that are able to leave water for extended periods of time. About 11 distantly related genera of fish are considered amphibious. This suggests that many fish genera independently evolved amphibious traits, a process known ...
, such as the
mudskipper
Mudskippers are any of the 23 extant species of amphibious fish from the subfamily Oxudercinae of the goby family Oxudercidae. They are known for their unusual body shapes, preferences for semiaquatic habitats, limited terrestrial locomotion ...
, which drag themselves across land on their sturdy fins. Among the
invertebrate
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chorda ...
s, most
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s – which includes the most diverse group of animals, the
insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pa ...
s – have a stance best described as sprawling. There is also anecdotal evidence that some
octopus
An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttlefish, ...
species (such as the genus ''
Pinnoctopus'') can also drag themselves across land a short distance by hauling their body along by their tentacles (for example to pursue prey between rockpools) – there may be video evidence of this. The semi-erect posture is more accurately interpreted as an extremely elevated sprawling posture. This mode of locomotion is typically found in large lizards such as
monitor lizard
Monitor lizards are lizards in the genus ''Varanus,'' the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, and one species is also found in the Americas as an invasive species. About 80 species are rec ...
s and
tegus.
Mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...
s and
bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...
s typically have a fully erect posture, though each evolved it independently. In these groups the legs are placed beneath the body. This is often linked with the evolution of
endothermy, as it avoids
Carrier's constraint and thus allows prolonged periods of activity. The fully erect stance is not necessarily the "most-evolved" stance; evidence suggests that crocodilians evolved a semi-erect stance in their forelimbs from ancestors with fully erect stance as a result of adapting to a mostly aquatic lifestyle, though their hindlimbs are still held fully erect. For example, the
mesozoic
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
prehistoric crocodilian ''
Erpetosuchus
''Erpetosuchus'' is an extinct genus of pseudosuchian from the Late Triassic. The type species of ''Erpetosuchus'' is ''E. granti''. It was first described by E. T. Newton in 1894 for remains found in northeastern Scotland, including four specim ...
'' is believed to have had a fully erect stance and been terrestrial.
Number of legs
The number of locomotory appendages varies much between animals, and sometimes the same animal may use different numbers of its legs in different circumstances. The best contender for
unipedal movement is the
springtail
Springtails (Collembola) form the largest of the three lineages of modern hexapods that are no longer considered insects (the other two are the Protura and Diplura). Although the three orders are sometimes grouped together in a class called ...
, which while normally
hexapedal, hurls itself away from danger using its
furcula, a
tail
The tail is the section at the rear end of certain kinds of animals’ bodies; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammal ...
-like forked rod that can be rapidly unfurled from the underside of its body.
A number of species move and stand on two legs, that is, they are
bipedal. The group that is exclusively bipedal is the
bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...
s, which have either an alternating or a hopping gait. There are also a number of bipedal
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...
s. Most of these move by hopping – including the
macropods such as
kangaroo
Kangaroos are four marsupials from the family Macropodidae (macropods, meaning "large foot"). In common use the term is used to describe the largest species from this family, the red kangaroo, as well as the antilopine kangaroo, eastern ...
s and various jumping
rodent
Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...
s. Only a few mammals such as
human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, cultu ...
s and the
ground pangolin
The ground pangolin (''Smutsia temminckii''), also known as Temminck's pangolin, Cape pangolin or steppe pangolin, is one of four species of pangolins which can be found in Africa, and the only one in southern and eastern Africa. The animal was n ...
commonly show an alternating bipedal gait. In humans, alternating bipedalism is characterized by a bobbing motion, which is due to the utilization of gravity when falling forward. This form of bipedalism has demonstrated significant energy savings.
Cockroach
Cockroaches (or roaches) are a paraphyletic group of insects belonging to Blattodea, containing all members of the group except termites. About 30 cockroach species out of 4,600 are associated with human habitats. Some species are well-known ...
es and some
lizard
Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia altho ...
s may also run on their two hind legs.
With the exception of the birds, terrestrial vertebrate groups with legs are mostly
quadrupedal – the mammals,
reptile
Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates ( lizards and snakes) and rhynchocephalia ...
s, and the
amphibian
Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbo ...
s usually move on four legs. There are many quadrupedal gaits.
The most diverse group of animals on earth, the
insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pa ...
s, are included in a larger
taxon
In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...
known as
hexapods, most of which are hexapedal, walking and standing on six legs. Exceptions among the insects include
praying mantises and
water scorpions, which are quadrupeds with their front two legs modified for grasping, some
butterflies
Butterflies are insects in the macrolepidopteran clade Rhopalocera from the order Lepidoptera, which also includes moths. Adult butterflies have large, often brightly coloured wings, and conspicuous, fluttering flight. The group comprises ...
such as the
Lycaenidae
Lycaenidae is the second-largest family of butterflies (behind Nymphalidae, brush-footed butterflies), with over 6,000 species worldwide, whose members are also called gossamer-winged butterflies. They constitute about 30% of the known butterf ...
(blues and hairstreaks) which use only four legs, and some kinds of insect
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
...
e that may have no legs (e.g.,
maggot
A maggot is the larva of a fly (order Diptera); it is applied in particular to the larvae of Brachycera flies, such as houseflies, cheese flies, and blowflies, rather than larvae of the Nematocera, such as mosquitoes and crane flies.
En ...
s), or additional
prolegs (e.g.,
caterpillar
Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths).
As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder Sy ...
s).
Spider
Spiders (order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...
s and many of their relatives move on eight legs – they are
octopedal. However, some creatures move on many more legs. Terrestrial
crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...
s may have a fair number –
woodlice
A woodlouse (plural woodlice) is an isopod crustacean from the polyphyleticThe current consensus is that Oniscidea is actually triphyletic suborder Oniscidea within the order Isopoda. They get their name from often being found in old wood ...
having fourteen legs. Also, as previously mentioned, some insect larvae such as caterpillars and
sawfly larvae have up to five (caterpillars) or nine (sawflies) additional fleshy prolegs in addition to the six legs normal for insects.
Some species of invertebrate have even more legs, the unusual
velvet worm
Onychophora (from grc, ονυχής, , "claws"; and , , "to carry"), commonly known as velvet worms (due to their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, '' Peripatus ...
having stubby legs under the length of its body, with around several dozen pairs of legs.
Centipedes have one pair of legs per body segment, with typically around 50 legs, but some species have over 200. The terrestrial animals with the most legs are the
millipedes. They have two pairs of legs per body segment, with common species having between 80 and 400 legs overall – with the rare species ''
Illacme plenipes'' having up to 750 legs.
Animals with many legs typically move them in
metachronal rhythm, which gives the appearance of waves of motion travelling forward or backward along their rows of legs. Millipedes, caterpillars, and some small centipedes move with the leg waves travelling forward as they walk, while larger centipedes move with the leg waves travelling backward.
Leg and foot structure
The
legs of
tetrapod
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...
s, the main group of terrestrial
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...
s (which also includes
amphibious fish
Amphibious fish are fish that are able to leave water for extended periods of time. About 11 distantly related genera of fish are considered amphibious. This suggests that many fish genera independently evolved amphibious traits, a process known ...
), have internal bones, with externally attached muscles for movement, and the basic form has three key
joints: the
shoulder joint, the
knee
In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the ...
joint, and the
ankle joint, at which the
foot
The foot ( : feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg mad ...
is attached. Within this form there is much variation in structure and shape. An alternative form of vertebrate 'leg' to the tetrapod leg is the fins found on
amphibious fish
Amphibious fish are fish that are able to leave water for extended periods of time. About 11 distantly related genera of fish are considered amphibious. This suggests that many fish genera independently evolved amphibious traits, a process known ...
. Also a few
tetrapod
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...
s, such as the
macropods, have adapted their
tail
The tail is the section at the rear end of certain kinds of animals’ bodies; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammal ...
s as additional locomotory appendages.
The fundamental form of the vertebrate
foot
The foot ( : feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg mad ...
has five digits, however some animals have fused digits, giving them less, and some early
fishapods had more;
Acanthostega had eight toes. Only
ichthyosaur
Ichthyosaurs (Ancient Greek for "fish lizard" – and ) are large extinct marine reptiles. Ichthyosaurs belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' – a designation introduced by Sir Richard Owen in 1842, alt ...
s evolved more than 5 digits ''within'' tetrapods, while their transition from land to water again (limb terminations were becoming flippers). Feet have evolved
many forms depending on the animal's needs. One key variation is where on the foot the animal's weight is placed. Some vertebrates: amphibians, reptiles, and some mammals such as
human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, cultu ...
s,
bear
Bears are carnivoran mammals of the family Ursidae. They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout the No ...
s, and rodents, are plantigrade. This means the weight of the body is placed on the heel of the foot, giving it strength and stability. Most mammals, such as
cats and
dogs are
digitigrade
In terrestrial vertebrates, digitigrade () locomotion is walking or running on the toes (from the Latin ''digitus'', 'finger', and ''gradior'', 'walk'). A digitigrade animal is one that stands or walks with its toes (metatarsals) touching the groun ...
, walking on their toes, giving them what many people mistake as a “backward knee”, which is really their ankle. The extension of the joint helps store momentum and acts as a spring, allowing digitigrade creatures more speed. Digitigrade mammals are also often adept at quiet movement. Birds are also digitigrade. Hooved mammals are known as
ungulates, walking on the fused tips of their fingers and toes. This can vary from odd-toed ungulates, such as horses, pigs, and a few wild African ungulates, to even-toed ungulates, such as cows, deer, and goats.
Mammals whose limbs have adapted to grab objects have what are called prehensile limbs. This term can be attributed to front limbs as well as tails for animals such as monkeys and some rodents. All animals that have prehensile front limbs are plantigrade, even if their ankle joint looks extended (squirrels are a good example).
Among terrestrial
invertebrate
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chorda ...
s there are a number of leg forms. The
arthropod legs are jointed and supported by hard external armor, with the muscles attached to the internal surface of this
exoskeleton
An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton ( endoskeleton) in for example, a human. In usage, some of the ...
. The other group of legged terrestrial invertebrates, the
velvet worms
Onychophora (from grc, ονυχής, , "claws"; and , , "to carry"), commonly known as velvet worms (due to their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, '' Peripatus ...
, have soft stumpy legs supported by a
hydrostatic skeleton. The
prolegs that some caterpillars have in addition to their six more-standard arthropod legs have a similar form to those of velvet worms, and suggest a distant shared ancestry.
Gaits
Animals show a vast range of
gait
Gait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed, terrain, the need to maneuver, and energetic efficiency. ...
s, the order that they place and lift their appendages in locomotion. Gaits can be grouped into categories according to their patterns of support sequence. For
quadrupeds, there are three main categories: 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.
Walking
Walking (also known as ambulation) is one of the main gaits of terrestrial locomotion among legged animals. Walking is typically slower than running and other gaits. Walking is defined by an ' inverted pendulum' gait in which the body vaults ...
is the most common gait, where some feet are on the ground at any given time, and found in almost all legged animals. In an informal sense,
running
Running is a method of terrestrial locomotion allowing humans and other animals to move rapidly on foot. Running is a type of gait characterized by an aerial phase in which all feet are above the ground (though there are exceptions). This i ...
is considered to occur when at some points in the stride all feet are off the ground in a moment of suspension. Technically, however, moments of suspension occur in both running gaits (such as trot) and leaping gaits (such as canter and gallop). Gaits involving one or more moments of suspension can be found in many animals, and compared to walking they are faster but more energetically costly forms of locomotion.
Animals will use different gaits for different speeds, terrain, and situations. For example, horses show four natural gaits, the slowest
horse gait
Horses can use various gaits (patterns of leg movement) during locomotion across solid ground, either naturally or as a result of specialized training by humans.Ensminger, M. E. ''Horses and Horsemanship'' 6th edition USA: Interstate Publishe ...
is the
walk
Walking (also known as ambulation) is one of the main gaits of terrestrial locomotion among legged animals. Walking is typically slower than running and other gaits. Walking is defined by an ' inverted pendulum' gait in which the body vaults ...
, then there are three faster gaits which, from slowest to fastest, are the
trot, the
canter
The canter and gallop are variations on the fastest gait that can be performed by a horse or other equine. The canter is a controlled three-beat gait, while the gallop is a faster, four-beat variation of the same gait. It is a natural gait p ...
, and the
gallop. Animals may also have unusual gaits that are used occasionally, such as for moving sideways or backwards. For example, the main
human gaits are bipedal
walking
Walking (also known as ambulation) is one of the main gaits of terrestrial locomotion among legged animals. Walking is typically slower than running and other gaits. Walking is defined by an ' inverted pendulum' gait in which the body vaults ...
and
running
Running is a method of terrestrial locomotion allowing humans and other animals to move rapidly on foot. Running is a type of gait characterized by an aerial phase in which all feet are above the ground (though there are exceptions). This i ...
, but they employ many other gaits occasionally, including a four-legged
crawl in tight spaces.
In walking, and for many animals running, the motion of legs on either side of the body alternates, i.e. is out of phase. Other animals, such as a horse when galloping, or an
inchworm
The geometer moths are moths belonging to the family Geometridae of the insect order Lepidoptera, the moths and butterflies. Their scientific name derives from the Ancient Greek ''geo'' γεω (derivative form of or "the earth"), and ''metro ...
, alternate between their front and back legs.
In saltation (hopping) all legs move together, instead of alternating. As a main means of locomotion, this is usually found in bipeds, or semi-bipeds. Among the mammals saltation is commonly used among
kangaroo
Kangaroos are four marsupials from the family Macropodidae (macropods, meaning "large foot"). In common use the term is used to describe the largest species from this family, the red kangaroo, as well as the antilopine kangaroo, eastern ...
s and their relatives,
jerboas,
springhares,
kangaroo rat
Kangaroo rats, small mostly nocturnal rodents of genus ''Dipodomys'', are native to arid areas of western North America. The common name derives from their bipedal form. They hop in a manner similar to the much larger kangaroo, but developed ...
s,
hopping mice
A hopping mouse is any of about ten different Australian native mice in the genus ''Notomys''. They are rodents, not marsupials, and their ancestors are thought to have arrived from Asia about 5 million years ago.
All are brown or fawn, fadin ...
,
gerbils, and
sportive lemur
The sportive lemurs are the medium-sized primates that make up the family Lepilemuridae. The family consists of only one extant genus, ''Lepilemur''. They are closely related to the other lemurs and exclusively live on the island of Madagascar. ...
s. Certain tendons in the hind legs of kangaroos are very
elastic
Elastic is a word often used to describe or identify certain types of elastomer, elastic used in garments or stretchable fabrics.
Elastic may also refer to:
Alternative name
* Rubber band, ring-shaped band of rubber used to hold objects togethe ...
, allowing kangaroos to effectively bounce along conserving energy from hop to hop, making saltation a very energy efficient way to move around in their nutrient poor environment. Saltation is also used by many small birds,
frog
A frog is any member of a diverse and largely Carnivore, carnivorous group of short-bodied, tailless amphibians composing the order (biology), order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-f ...
s,
flea
Flea, the common name for the order Siphonaptera, includes 2,500 species of small flightless insects that live as external parasites of mammals and birds. Fleas live by ingesting the blood of their hosts. Adult fleas grow to about long, ...
s,
crickets,
grasshopper
Grasshoppers are a group of insects belonging to the suborder Caelifera. They are among what is possibly the most ancient living group of chewing herbivorous insects, dating back to the early Triassic around 250 million years ago.
Grasshopp ...
s, and
water fleas
The Diplostraca or Cladocera, commonly known as water fleas, are a superorder of small crustaceans that feed on microscopic chunks of organic matter (excluding some predatory forms).
Over 1000 species have been recognised so far, with many more ...
(a small
plankton
Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cruc ...
ic
crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...
).
Most animals move in the direction of their head. However, there are some exceptions.
Crab
Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all th ...
s move sideways, and
naked mole rats, which live in tight tunnels and can move backward or forward with equal facility.
Crayfish can move backward much faster than they can move forward.
Gait analysis is the study of gait in humans and other animals. This may involve videoing subjects with markers on particular anatomical landmarks and measuring the forces of their footfall using floor
transducer
A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another.
Transducers are often employed at the boundaries of automation, measurement, and con ...
s (
strain gauge
A strain gauge (also spelled strain gage) is a device used to measure strain on an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports ...
s). Skin
electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials ...
s may also be used to measure
muscle
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of mus ...
activity.
Limbless locomotion
There are a number of terrestrial and amphibious
limbless vertebrates and invertebrates. These animals, due to lack of appendages, use their bodies to generate propulsive force. These movements are sometimes referred to as "slithering" or "crawling", although neither are formally used in the scientific literature and the latter term is also used for some animals moving on all four limbs. All limbless animals come from
cold-blooded groups; there are no
endothermic
In thermochemistry, an endothermic process () is any thermodynamic process with an increase in the enthalpy (or internal energy ) of the system.Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015).''Principle of Modern Chemistry'', Brooks Cole. ...
limbless animals, i.e. there are no limbless birds or mammals.
Lower body surface
Where the foot is important to the legged mammal, for limbless animals the underside of the body is important. Some animals such as
snake
Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more ...
s or
legless lizards move on their smooth dry underside. Other animals have various features that aid movement.
Mollusc
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is est ...
s such as
slug
Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced shell, or only a ...
s and
snail
A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class ...
s move on a layer of
mucus
Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It ...
that is secreted from their underside, reducing friction and protecting from injury when moving over sharp objects.
Earthworm
An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. T ...
s have small bristles (
setae
In biology, setae (singular seta ; from the Latin word for "bristle") are any of a number of different bristle- or hair-like structures on living organisms.
Animal setae
Protostomes
Annelid setae are stiff bristles present on the body. ...
) that hook into the substrate and help them move. Some animals, such as
leeches
Leeches are segmented parasitic or predatory worms that comprise the subclass Hirudinea within the phylum Annelida. They are closely related to the oligochaetes, which include the earthworm, and like them have soft, muscular segmented b ...
, have suction cups on either end of the body allowing
two anchor movement.
Type of movement
Some limbless animals, such as leeches, have suction cups on either end of their body, which allow them to move by anchoring the 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
two-anchor movement. A legged animal, the
inchworm
The geometer moths are moths belonging to the family Geometridae of the insect order Lepidoptera, the moths and butterflies. Their scientific name derives from the Ancient Greek ''geo'' γεω (derivative form of or "the earth"), and ''metro ...
, also moves like this, clasping with appendages at either end of its body.
Limbless animals can also move using
pedal locomotory waves, rippling the underside of the body. This is the main method used by
mollusc
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is est ...
s such as slugs and snails, and also large flatworms, some other worms, and even
earless seals. The waves may move in the opposite direction to motion, known as
retrograde waves, or in the same direction as motion, known as
direct waves. Earthworms move by retrograde waves alternatively swelling and contracting down the length of their body, the swollen sections being held in place using
setae
In biology, setae (singular seta ; from the Latin word for "bristle") are any of a number of different bristle- or hair-like structures on living organisms.
Animal setae
Protostomes
Annelid setae are stiff bristles present on the body. ...
. Aquatic molluscs such as
limpet
Limpets are a group of aquatic snails that exhibit a conical gastropod shell, shell shape (patelliform) and a strong, muscular foot. Limpets are members of the class Gastropoda, but are polyphyletic, meaning the various groups called "limpets" ...
s, which are sometimes out of the water, tend to move using retrograde waves. However, terrestrial molluscs such as slugs and snails tend to use direct waves.
Lugworms and seals also use direct waves.
Most
snakes
Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more j ...
move using
lateral undulation where a lateral wave travels down the snake's body in the opposite direction to the snake's motion and pushes the snake off irregularities in the ground. This mode of locomotion requires these irregularities to function. Another form of locomotion,
rectilinear locomotion, is used at times by some snakes, especially large ones such as
pythons and
boa. Here large scales on the underside of the body, known as
scutes are used to push backwards and downwards. This is effective on a flat surface and is used for slow, silent movement, such as when stalking prey. Snakes use
concertina locomotion for moving slowly in tunnels, here the snake alternates in bracing parts of its body on it surrounds. Finally the
caenophidian snakes use the fast and unusual method of movement known as
sidewinding on sand or loose soil. The snake cycles through throwing the front part of its body in the direction of motion and bringing the back part of its body into line crosswise.
Rolling
Although animals have never evolved
wheels for locomotion,
a small number of animals will move at times by
rolling their whole body. Rolling animals can be divided into those that roll under the force of gravity or wind and those that roll using their own power.
Gravity or wind assisted
The
web-toed salamander, a salamander, lives on steep hills in the
Sierra Nevada
The Sierra Nevada () is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies primar ...
mountains. When disturbed or startled it coils itself up into a ball, often causing it to roll downhill.
The
pebble toad (''Oreophrynella nigra'') lives atop
tepui
A tepui , or tepuy (), is a table-top mountain or mesa found in South America, especially in Venezuela and western Guyana. The word tepui means "house of the gods" in the native tongue of the Pemon, the indigenous people who inhabit the Gra ...
in the
Guiana highlands
The Guianas, sometimes called by the Spanish loan-word ''Guayanas'' (''Las Guayanas''), is a region in north-eastern South America which includes the following three territories:
* French Guiana, an overseas department and region of France
* ...
of
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...
. When threatened, often by
tarantula
Tarantulas comprise a group of large and often hairy spiders of the family Theraphosidae. , 1,040 species have been identified, with 156 genera. The term "tarantula" is usually used to describe members of the family Theraphosidae, although m ...
s, it rolls into ball, and typically being on an incline, rolls away under gravity like a loose pebble.
Namib wheeling spiders (''
Carparachne
''Carparachne'' is a genus of Namibian huntsman spiders that was first described by R. F. Lawrence in 1962. it contains two species, found in Namibia: '' C. alba'' and '' C. aureoflava''. The golden wheel spider (''C. aureoflava'') uses cartwhee ...
spp.''), found in the
Namib desert, will actively roll down sand dunes. This action can be used to successfully escape predators such as the ''
Pompilidae''
tarantula wasps, which lay their eggs in a paralyzed spider for their larvae to feed on when they hatch. The spiders flip their body sideways and then cartwheel over their bent legs. The rotation is fast, the
golden wheel spider (''Carparachne aureoflava'') moving up to 20 revolutions per second, moving the spider at 1 metre per second.
Coastal tiger beetle larvae when threatened can flick themselves into the air and curl their bodies to form a wheels, which the wind blows, often uphill, as far as 25 m and as fast as . The also may have some ability to steer themselves in this state.
Pangolin
Pangolins, sometimes known as scaly anteaters, are mammals of the order Pholidota (, from Ancient Greek ϕολιδωτός – "clad in scales"). The one extant family, the Manidae, has three genera: '' Manis'', ''Phataginus'', and '' Smuts ...
s, a type of mammal covered in thick scales, roll into a tight ball when threatened. Pangolins have been reported to roll away from danger, by both gravity and self-powered methods. A pangolin in hill country in
Sumatra
Sumatra is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the sixth-largest island in the world at 473,481 km2 (182,812 mi.2), not including adjacent i ...
, to flee from the researcher, ran 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
Caterpillars of the mother-of-pearl moth, ''
Pleuroptya ruralis
''Patania ruralis'', the mother of pearl moth, is a species of moth of the family Crambidae. It was described by Giovanni Antonio Scopoli in 1763. It is found in Europe.
The wingspan is . The forewings are pale whitish-ochreous, yellowish-ti ...
'', when attacked, will touch their heads to their tails and roll backwards, up to 5 revolutions at about 40 cm per second, which is about 40 times its normal speed.
''
Nannosquilla decemspinosa
''Nannosquilla decemspinosa'' is a species of long-bodied, short-legged mantis shrimp. It lives in shallow sandy areas along the Pacific coast of Central and South America.
It is most well known because when stranded by a low tide
Tides ...
'', a species of long-bodied, short-legged
mantis shrimp, lives in shallow sandy areas along the Pacific coast of Central and South America. When stranded by a low tide the 3 cm stomatopod lies on its back and performs backwards somersaults over and over. The animal moves up to 2 meters at a time by rolling 20–40 times, with speeds of around 72 revolutions per minute. That is 1.5 body lengths per second (3.5 cm/s). Researchers estimate that the stomatopod acts as a true wheel around 40% of the time during this series of rolls. The remaining 60% of the time it has to "jumpstart" a roll by using its body to thrust itself upwards and forwards.
Pangolin
Pangolins, sometimes known as scaly anteaters, are mammals of the order Pholidota (, from Ancient Greek ϕολιδωτός – "clad in scales"). The one extant family, the Manidae, has three genera: '' Manis'', ''Phataginus'', and '' Smuts ...
s have also been reported to roll away from danger by self-powered methods. Witnessed by a lion researcher
in the
Serengeti
The Serengeti ( ) ecosystem is a geographical region in Africa, spanning northern Tanzania. The protected area within the region includes approximately of land, including the Serengeti National Park and several game reserves. The Serenget ...
in Africa, a group of lions surrounded a pangolin, but could not get purchase on it when it rolled into a ball, and so the lions sat around it waiting and dozing. Surrounded by lions, it would unroll itself slightly and give itself a push to roll some distance, until by doing this multiple times it could get far enough away from the lions to be safe. Moving like this would allow a pangolin to cover distance while still remaining in a protective armoured ball.
Moroccan flic-flac spider
''Cebrennus rechenbergi'', also known as the Moroccan flic-flac spider and cartwheeling spider, is a species of huntsman spider indigenous to the sand dunes of the Erg Chebbi desert in Morocco. If provoked or threatened it can escape by doubling ...
s, if provoked or threatened, can escape by doubling their normal walking speed using forward or backward flips similar to acrobatic
flic-flac
Because ballet became formalized in France, a significant part of ballet terminology is in the French language.
A
À la seconde
() (Literally "to second") If a step is done "à la seconde," it is done to the side. 'Second position'. It can also ...
movements.
Limits and extremes
The fastest terrestrial animal is the
cheetah, which can attain maximal sprint speeds of approximately 104 km/h (64 mph).
The fastest running lizard is the
black iguana, which has been recorded moving at speed of up to 34.9 km/h (21.7 mph).
See also
*
Animal locomotion
*
Aquatic locomotion
Aquatic locomotion or swimming is biologically propelled motion through a liquid medium. The simplest propulsive systems are composed of cilia and flagella. Swimming has evolved a number of times in a range of organisms including arthropods, ...
*
Comparative foot morphology
*
Locomotion in space
*
Robot locomotion
*
Role of skin in locomotion
Role of skin in locomotion describes how the integumentary system is involved in locomotion. Typically the integumentary system can be thought of as skin, however the integumentary system also includes the segmented exoskeleton in arthropods and ...
*
Terrestrial
*
Undulatory locomotion
*
Walking fish
References
Bibliography
*
External links
*Adaptations of running animals
Crocodile stanceLecture on crawling (slithering) at Berkeley
{{DEFAULTSORT:Terrestrial Locomotion
Zoology
Articles containing video clips