Terrestrial locomotion has evolved as
animalAnimals are a major group of mostly multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously...
s adapted from aquatic to terrestrial environments.
LocomotionAnimal locomotion, which is the act of self-propulsion by an animal, has many manifestations, including running, jumping and flying. Animals move for a variety of reasons, such as to find food, a mate, or a suitable microhabitat, and to escape predators...
on land raises different problems than that on water, with reduced
frictionFriction is the force resisting the relative lateral motion of solid surfaces, fluid layers, or material elements in contact. It is usually subdivided into several varieties:...
being replaced by the effects of gravity.
There are three basic forms of locomotion found among terrestrial animals
- Legged - Moving by using appendage
An appendage in the broadest sense is an additional or subsidiary part existing on, or added to, something which can generally still function if the appendage has never existed or is later provided or grown, or will still perform a primary function if the appendage is removed.- Biological context...
s
- Limbless locomotion - moving without legs, primarily using the body itself as a propulsive structure.
- Rolling - rotating the body over the substrate
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
vertebrateVertebrates are members of the subphylum Vertebrata, chordates with backbones or spinal columns. About 58,000 species of vertebrates have been described. Vertebrata is the largest subphylum of chordates, and contains many familiar groups of large land animals. Vertebrates comprise cyclostomes, bony...
s and the
arthropodAn arthropod is an invertebrate that has an exoskeleton , a segmented body, and jointed attachments called appendages. Arthropods are animals belonging to the Phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s. Important aspects of legged locomotion are
stanceStance is a morpheme meaning stand, used in several ways:* to take a position in an argument, a stand on a given issue;* refers to a particular standing postureThere are also a wide variety of stances adopted in martial arts and sports:* boxing stances...
(the way the body is supported by the legs), the number of legs, and the functional structure of the
legŁęg may refer to the following places in Poland:*A former name for the town of Ełk *Łęg, Lower Silesian Voivodeship *Łęg, Kuyavian-Pomeranian Voivodeship *Łęg, Łódź Voivodeship...
and
footThe foot is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion...
. There are also many
gaitGait is the pattern of movement of the limbs of terrestrial animals, including humans, during locomotion. 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 in order to locomote, such as
walkingWalking is the main form of animal locomotion on land, distinguished from running and crawling. When carried out in shallow waters, it is usually described as wading and when performed over a steeply rising object or an obstacle it becomes scrambling or climbing...
,
runningRunning is a means for an animal to move on foot. It is defined in sporting terms as a gait in which at some point all feet are off the ground at the same time. This is in contrast to walking, where one foot is always in contact with the ground, the legs are kept mostly straight and the center of...
, or
hoppingHopping may refer to:In activities:* Hopping, an alternative term for jumping, especially on one foot.* Freighthopping, the act of surreptitiously riding on a railroad freight car.* Island hopping, a series of journeys between islands....
.
Stance
Appendages can be used for movement in a number of ways. The
stanceStance is a morpheme meaning stand, used in several ways:* to take a position in an argument, a stand on a given issue;* refers to a particular standing postureThere are also a wide variety of stances adopted in martial arts and sports:* boxing stances...
, the way the body is supported by the legs, is an important aspect. Charig 1972 identified three main ways in which vertebrates support themselves with their legs - the sprawling stance, the semi-erect stance, and the fully erect stance. Some animals may use different stances in different circumstances, depending on the stance's mechanical and energetic advantages.
The most basic is the sprawling stance. Here the legs are used to drag the body over the land. This is the earliest form of use of legs on land.
Amphibious fishAmphibious 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. These fish use a range of terrestrial locomotory modes, such as...
such as the
mudskipperMudskippers are members of the subfamily Oxudercinae , within the family Gobiidae . They are completely amphibious fish, fish that can use its pectoral fins to "walk" on land...
drag themselves across land on their sturdy fins. Many reptiles and amphibians, some or all of the time, use this method of locomotion. Among
invertebrateAn invertebrate is an animal without a vertebral column. The group includes 95% of all animal species — all animals except those in the Chordate subphylum Vertebrata ....
s there is anecdotal evidence that some
octopusThe octopus is a cephalopod of the order Octopoda. The octopus inhabits many diverse regions of the ocean, especially coral reefs. The term may also be used to refer only to those creatures in the genus Octopus...
species (such as the
PinnoctopusPinnoctopus is a genus of octopuses in the family Octopodidae.-Species:* Pinnoctopus cordiformis Quoy and Gaimard, 1832.* Pinnoctopus kermadecensis-Taxonomic note:...
genus), sometimes to pursue prey between rockpools, can also drag themselves across land a short distance by hauling its body along by it tentacles. There may be video evidence of this.
The second form of stance found among legged terrestrial animals is the semi-erect stance. Here the legs are to the side, but the body is held above the substrate. This mode of locomotion is found among some
reptileReptiles, or members of the class Reptilia, are air-breathing, generally "cold-blooded" amniotes that generally have skin covered in scales or scutes. They are tetrapods and lay amniote eggs, whose embryos are surrounded by the amnion membrane...
s and
amphibianAmphibians , such as frogs, toads, salamanders, newts, and caecilians, are ectothermic animals that metamorphose from a juvenile water-breathing form, to an adult air-breathing form. Though amphibians typically have four limbs, the Caecilians are notable for being limbless. Unlike other land...
s. It is also the main stance of the crocodilians. A few mammals, such as the
platypusThe Platypus is a semi-aquatic mammal endemic to eastern Australia, including Tasmania. Together with the four species of echidna, it is one of the five extant species of monotremes, the only mammals that lay eggs instead of giving birth to live young...
also use this stance. Among the
invertebrateAn invertebrate is an animal without a vertebral column. The group includes 95% of all animal species — all animals except those in the Chordate subphylum Vertebrata ....
s most
arthropodAn arthropod is an invertebrate that has an exoskeleton , a segmented body, and jointed attachments called appendages. Arthropods are animals belonging to the Phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s, which includes the most diverse group of animals - the
insectInsects are arthropods, having a hard exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae. They are the most diverse group of animals on the planet and include more than a million species that are already described. Insects represent more than half of all...
s, many have a stance which might best be described as semi-erect.
Finally there is the main form of stance of
mammalMammals are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.Mammals are divided into three main...
and
birdBirds are winged, bipedal, endothermic , vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the Bee Hummingbird to the ...
s, the fully erect stance. In these groups the legs are placed beneath the body. This is often linked with the evolution of endothermy, as it avoids
Carrier's constraintCarrier's constraint is the observation that air-breathing vertebrates which have two lungs and flex their bodies sideways during locomotion find it very difficult to move and breathe at the same time, because:...
and thus allows prolonged periods of activity (Bakker 1988). The fully erect stance is not necessarily the "most-evolved" stance; evidence suggests that crocodilians evolved a semi-erect stance from ancestors with fully erect stance as a result of adapting to a mostly aquatic lifestyle (Reilly & Elias 1998). For example, the
mesozoicThe Mesozoic Era is one of three geologic eras of the Phanerozoic eon. The division of time into eras dates back to Giovanni Arduino, in the 18th century, although his original name for the era now called the "Mesozoic" was "Secondary" The Mesozoic Era is one of three geologic eras of the...
prehistoric crocodilian
ErpetosuchusErpetosuchus is an extinct genus of crurotarsan from the Late Triassic. It was first described by E. T. Newton in 1894 for remains found in northeastern Scotland, with more remains found in the United States in recent years. Erpetosuchus is the sister-taxon to Crocodylomorpha.The type species of...
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
springtailSpringtails form the largest of the three lineages of modern hexapods that are no longer considered insects...
, which while normally hexapedal, hurls itself away from danger using its
furculaThe furcula is a tail-like appendage shaped like a fork, found on the fourth abdominal segment of springtails. Present in most species, it is used for jumping when the animal is threatened. While at rest, it is folded under the abdomen and held there by a structure called a "retinaculum", located...
, a
tailThe tail is the section at the rear end of an animal's body; 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 mammals and birds...
-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
birdBirds are winged, bipedal, endothermic , vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the Bee Hummingbird to the ...
s, which have either an alternating or a hopping gait. There are also a number of bipedal mammals. Most of these move by hopping – such as the
macropodMacropods are marsupials belonging to the family Macropodidae, which includes kangaroos, wallabies, tree-kangaroos, pademelons, and several others. Before European settlement, there were about 53 species of Macropods. Six species have since become extinct. Another 11 species have been greatly...
s and various jumping
rodentRodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
s. Only a few mammals such as
humanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
s and the
giant pangolinThe Giant Pangolin is a pangolin species. Members of the species inhabit Africa with a range stretching along the equator from west Africa to Uganda. The Giant Pangolin is the largest species of pangolin, or "scaly anteaters" – the large, scaled mammals belonging to the Manidae family. It...
commonly show an alternating bipedal gait. Also
cockroachCockroaches are insects of the order Blattaria. This name derives from the Latin name for the insect, Blatta....
es and some
lizardLizards are a very large and widespread group of squamate reptiles, with nearly 5,000 species, ranging across all continents except Antarctica as well as most oceanic island chains...
s may run on their two hind legs.
MacropodMacropods are marsupials belonging to the family Macropodidae, which includes kangaroos, wallabies, tree-kangaroos, pademelons, and several others. Before European settlement, there were about 53 species of Macropods. Six species have since become extinct. Another 11 species have been greatly...
s such as
kangarooA kangaroo is a marsupial from the family Macropodidae . In common use the term is used to describe the largest species from this family, especially those of genus Macropus, Red Kangaroo, Antilopine Kangaroo, Eastern and Western Grey Kangaroo...
s are the only mammalian example of
tripedalTripedal is the term used for any animal that stands on three legs. The terms bipedal and quadrupedal are used more commonly when referring to animals that either walk on two legs Tripedal (from the Latin tri = three + ped = foot) is the term used for (or would be used for) any animal that stands...
movement. They have thick muscular tails and when moving slowly may alternate between resting their weight on their tails and their two hind legs.
With the exception of the
birdBirds are winged, bipedal, endothermic , vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the Bee Hummingbird to the ...
s, all terrestrial vertebrate groups with legs are mostly quadrupedal – the
mammalMammals are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.Mammals are divided into three main...
s,
reptileReptiles, or members of the class Reptilia, are air-breathing, generally "cold-blooded" amniotes that generally have skin covered in scales or scutes. They are tetrapods and lay amniote eggs, whose embryos are surrounded by the amnion membrane...
s, and the
amphibianAmphibians , such as frogs, toads, salamanders, newts, and caecilians, are ectothermic animals that metamorphose from a juvenile water-breathing form, to an adult air-breathing form. Though amphibians typically have four limbs, the Caecilians are notable for being limbless. Unlike other land...
s usually move on four legs. There are many quadrupedal gaits.
The most diverse group of animals on earth, the
insectInsects are arthropods, having a hard exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae. They are the most diverse group of animals on the planet and include more than a million species that are already described. Insects represent more than half of all...
s, are included in a larger
taxon|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement. Defining what belongs or does not belong to such a...
known as
hexapodsThe subphylum Hexapoda constitutes the largest grouping of arthropods and includes the insects as well as three much smaller groups of wingless arthropods: Collembola, Protura, and Diplura . The Collembola are very abundant in terrestrial environments...
, most of which are hexapedal, walking and standing on six legs. Exceptions among the insects include praying mantises and water scorpions which are quadrapeds, their front two legs having been modified for grasping, some
butterfliesA butterfly is an insect of the order Lepidoptera. Like all Lepidoptera, butterflies are notable for their unusual life cycle with a larval caterpillar stage, an inactive pupal stage, and a spectacular metamorphosis into a familiar and colourful winged adult form. Most species are day-flying so...
which use only four legs, and some kinds of insect
larvaA larva is a young form of animal with indirect development, going through or undergoing metamorphosis ....
e which may have no legs (e.g.
maggotMaggot is the common name of the larval phase of development in insects of the order Diptera . Sometimes the word is used to denote the larval stage of any insects.-Fishing:...
s), or additional
prolegProlegs are the fleshy, stubby little structures found on the ventral surface of the abdomen of most larval forms of insects of the Order Lepidoptera, though they can also be found on other larval insects such as sawflies and a few types of flies. Prolegs of lepidopteran larvae have a small circle...
s (e.g.
caterpillarCaterpillars are the larval form of a member of the order Lepidoptera . They are mostly phytophagous in food habit, with some species being entomophagous. Caterpillars are voracious feeders and many of them are considered pests in agriculture...
s).
SpiderSpiders are air-breathing chelicerate arthropods that have eight legs, and chelicerae modified into fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms...
s and many of their relatives move on eight legs - are octopedal. However, some creatures move on many more legs. Terrestrial
crustaceanCrustaceans are a very large group of arthropods, comprising almost 52,000 described species , and are usually treated as a subphylum . They include various familiar animals, such as crabs, lobsters, crayfish, shrimp, krill and barnacles...
s may have a fair number - woodlice having fourteen legs. Also, as previously mentioned, some insect larvae such as
caterpillarCaterpillars are the larval form of a member of the order Lepidoptera . They are mostly phytophagous in food habit, with some species being entomophagous. Caterpillars are voracious feeders and many of them are considered pests in agriculture...
s and
sawflySawfly is the common name for insects belonging to suborder Symphyta of the order Hymenoptera. Sawflies are distinguishable from most other Hymenoptera by the broad connection between the abdomen and the thorax, and by their caterpillar-like larvae...
larvae have up to five (caterpillars) or nine (sawflies) additional fleshy
prolegProlegs are the fleshy, stubby little structures found on the ventral surface of the abdomen of most larval forms of insects of the Order Lepidoptera, though they can also be found on other larval insects such as sawflies and a few types of flies. Prolegs of lepidopteran larvae have a small circle...
s in addition to the six legs normal for insects. Some species of invertebrate have even more legs, the unusual
velvet wormThe velvet worms are a minor Ecdysozoan phylum. The segmented worm-like organisms have tiny eyes, antennae, multiple pairs of legs and slime glands. Most common in tropical regions of the Southern Hemisphere, they prey on smaller animals such as insects, which they catch by squirting an adhesive...
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 having over 200. The terrestrial animals with the most legs are the
millipedeMillipedes, known as shongololos in South African English, are arthropods that have two pairs of legs per segment . Each segment that has two pairs of legs is a result of two single segments fused together as one...
s. They have two pairs of legs per body segment, with common species having between 80 and 400 legs overall – with the rare species
Illacme plenipesIllacme plenipes is a millipede found in the central region of the U.S. state of California. Although no millipede has one thousand legs, Illacme plenipes comes the closest with one recorded specimen having 750 legs. On average they have over 600 legs, twice the average for millipede species...
having up to 750 legs. Animals with many legs typically move by waves of motion travelling along their legs.
Leg and foot structure
The
legŁęg may refer to the following places in Poland:*A former name for the town of Ełk *Łęg, Lower Silesian Voivodeship *Łęg, Kuyavian-Pomeranian Voivodeship *Łęg, Łódź Voivodeship...
s of
tetrapodTetrapods are vertebrate animals having four feet, legs or leglike appendages. Amphibians, reptiles, dinosaurs/birds, and mammals are all tetrapods, and even the limbless snakes are tetrapods by descent...
s, the main group of terrestrial
vertebrateVertebrates are members of the subphylum Vertebrata, chordates with backbones or spinal columns. About 58,000 species of vertebrates have been described. Vertebrata is the largest subphylum of chordates, and contains many familiar groups of large land animals. Vertebrates comprise cyclostomes, bony...
s, have internal bones, with externally attached muscles for movement, and the basic form has three key
jointA joint is the location at which two or more bones make contact. They are constructed to allow movement and provide mechanical support, and are classified structurally and functionally.-Classification:...
s: the
shoulderIn human anatomy, the shoulder joint comprises the part of the body where the humerus attaches to the scapula. The shoulder refers to the group of structures in the region of the joint....
joint, the
kneeThe knee joint joins the thigh with the leg and consists of two articulations: one between the femur and tibia, and one between the femur and patella. It is the largest and most complicated joint in the human body. The knee is a mobile trocho-ginglymus , which permits flexion and extension as well...
joint, and the
ankleIn human anatomy, the ankle joint is formed where the foot and the leg meet. The ankle, or talocrural joint, is a synovial hinge joint that connects the distal ends of the tibia and fibula in the lower limb with the proximal end of the talus bone in the foot...
joint, at which the
footThe foot is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion...
is attached. Within this theme there is much variation in form. An alternative form of vertebrate 'leg' to the tetrapod leg is the fins found on
amphibious fishAmphibious 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. These fish use a range of terrestrial locomotory modes, such as...
. Also a few
tetrapodTetrapods are vertebrate animals having four feet, legs or leglike appendages. Amphibians, reptiles, dinosaurs/birds, and mammals are all tetrapods, and even the limbless snakes are tetrapods by descent...
s, such as the
macropodMacropods are marsupials belonging to the family Macropodidae, which includes kangaroos, wallabies, tree-kangaroos, pademelons, and several others. Before European settlement, there were about 53 species of Macropods. Six species have since become extinct. Another 11 species have been greatly...
s, have adapted their
tailThe tail is the section at the rear end of an animal's body; 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 mammals and birds...
s as additional locomotory appendages.
The basic form of the vertebrate
footThe foot is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion...
has five
toeToes are the digits of the foot of an animal. Animal species such as cats that walk on their toes are described as being digitigrade. Humans, and other animals that walk on the soles of their feet, are described as being plantigrade; unguligrade animals are those that walk on hooves at the tips of...
s, however some animals will have evolved fewer than this, and some early
tetrapodTetrapods are vertebrate animals having four feet, legs or leglike appendages. Amphibians, reptiles, dinosaurs/birds, and mammals are all tetrapods, and even the limbless snakes are tetrapods by descent...
s had more;
AcanthostegaAcanthostega is an extinct tetrapod genus, among the first vertebrate animals to have recognizable limbs. It appeared in the Upper Devonian about 365 million years ago, and was anatomically intermediate between lobe-finned fishes and the first tetrapods fully capable of coming onto...
had eight toes. 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. Most vertebrates—the amphibians, the reptiles, and some mammals such as
humanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
s and
bearBears are mammals of the family Ursidae. Bears are classified as caniforms, or doglike carnivorans, with the pinnipeds being their closest living relatives. Although there are only eight living species of bear, they are widespread, appearing in a wide variety of habitats throughout the Northern...
s—are
plantigraderight|151px|thumb|Human skeleton, showing plantigrade habitIn mammals, plantigrade locomotion means walking with the podials and metatarsals flat on the ground....
, walking on the whole of the underside of the foot. Many mammals, such as
catThe cat , also known as the domestic cat or housecat to distinguish it from other felines and felids, is a small carnivorous mammal that is valued by humans for its companionship and its ability to hunt vermin and household pests...
s and
dogThe dog is a domesticated form of the Gray Wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The domestic dog has been one of the most widely kept working and companion animals in human history...
s are
digitigradeA digitigrade is an animal that stands or walks on its digits, or toes. Digitigrades include walking birds , cats, dogs, and most other mammals, but not humans, bears, and a few others...
, walking on their toes, the greater stride length allowing more speed. Digitigrade mammals are also often adept at quiet movement. Birds are also digitigrade. Some animals such as
horseThe horse is a hoofed mammal, a subspecies of one of seven extant species of the family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s are unguligrade, walking on the tips of their toes. This even further increases their stride length and thus their speed. A few mammals are also known to walk on their
knuckleThe knuckles are the joints of the fingers and toes, which are brought into prominence when the hand is clenched and a fist is made. The word is derived from the diminutive of a word for bone, found in German Knochen/Knöchlein. Medically, it is said that the knuckles are formed by the...
s, at least for their front legs.
Knuckle-walkingKnuckle-walking is a form of quadrupedal walking in which the forelimbs hold the fingers in a partially flexed posture that allows body weight to press down on the ground through the knuckles....
allows the foot (hand) to specialise for food gathering and/or climbing, as with the great apes and the extinct
chalicothereChalicotheres were a group of herbivorous, odd-toed ungulates mammals spread throughout North America, Europe, Asia, and Africa during the Early Eocene to Early Pleistocene subepochs living from 55.8 mya—781,000 years ago, existing for approximately .They evolved around 40 million years ago from...
s, or for swimming, as with the
platypusThe Platypus is a semi-aquatic mammal endemic to eastern Australia, including Tasmania. Together with the four species of echidna, it is one of the five extant species of monotremes, the only mammals that lay eggs instead of giving birth to live young...
. In animals where feet have evolved into functional
handThe hands are the two intricate, prehensile, multi-fingered body parts normally located at the end of each arm of a primate. They are the chief organs for physically manipulating the environment, used for both gross motor skills and fine motor skills...
s,
hand walkingHand walking is an unusual form of human locomotion in which a person travels in a vertically inverted orientation with all body weight resting on the hands.It can be executed with legs fully extended or with variations such as stag, straddle or front splits...
is also possible.
Among terrestrial
invertebrateAn invertebrate is an animal without a vertebral column. The group includes 95% of all animal species — all animals except those in the Chordate subphylum Vertebrata ....
s there are a number of leg forms. The
arthropod legThe arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments are of Latin origin, and may be confused with terms for bones: coxa , trochanter , femur, tibia, tarsus, ischium, metatarsus, carpus, dactylus The arthropod...
s are jointed and supported by hard external armor, with the muscles attached to the internal surface of this
exoskeletonAn exoskeleton is an external skeleton that supports and protects an animal's body, in contrast to the internal endoskeleton of, for example, a human. Some animals, such as the tortoise, have both an endoskeleton and an exoskeleton...
. The other group of legged terrestrial invertebrates, the velvet worms, have soft stumpy legs supported by a
hydrostatic skeletonA hydrostatic skeleton or hydroskeleton is a structure found in many cold-blooded organisms and soft-bodied animals consisting of a fluid-filled cavity, the coelom, surrounded by muscles. The pressure of the fluid and action of the surrounding muscles are used to change an organism's shape and...
. The
prolegProlegs are the fleshy, stubby little structures found on the ventral surface of the abdomen of most larval forms of insects of the Order Lepidoptera, though they can also be found on other larval insects such as sawflies and a few types of flies. Prolegs of lepidopteran larvae have a small circle...
s 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
gaitGait is the pattern of movement of the limbs of terrestrial animals, including humans, during locomotion. 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, there are 60 discrete patterns: 37 walking gaits, 14 running gaits, and 9 leaping gaits.
WalkingWalking is the main form of animal locomotion on land, distinguished from running and crawling. When carried out in shallow waters, it is usually described as wading and when performed over a steeply rising object or an obstacle it becomes scrambling or climbing...
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,
runningRunning is a means for an animal to move on foot. It is defined in sporting terms as a gait in which at some point all feet are off the ground at the same time. This is in contrast to walking, where one foot is always in contact with the ground, the legs are kept mostly straight and the center of...
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 gaitHorse gaits are the different ways in which a horse can move, either naturally or as a result of specialized training by humans.-Classification:...
is the walk, then there are three faster gaits which, from slowest to fastest, are the
trotThe trot is a two beat diagonal gait of the horse where the diagonal pairs of legs move forward at the same time. There is a moment of suspension between each beat....
, the
canterThe canter is a controlled, three-beat gait performed by a horse. It is a natural gait possessed by all horses, faster than most horses' trot but slower than the gallop, and is used by all riders. The speed of the canter varies between 16-27 km/h , depending on the length of the stride of the horse...
, 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 gaitsHuman gait is the way locomotion is achieved using human limbs. For this article different gaits do not require changes in the geometry of motion, but rather, changes in the contact with the surface .-Walks:...
are bipedal
walkingWalking is the main form of animal locomotion on land, distinguished from running and crawling. When carried out in shallow waters, it is usually described as wading and when performed over a steeply rising object or an obstacle it becomes scrambling or climbing...
and
runningRunning is a means for an animal to move on foot. It is defined in sporting terms as a gait in which at some point all feet are off the ground at the same time. This is in contrast to walking, where one foot is always in contact with the ground, the legs are kept mostly straight and the center of...
, but they employ many other gaits occasionally, including a four-legged
crawlCrawling may refer to:*Limbless locomotion, the movement of limbless animals over the ground*Sprawling locomotion, the movement of limbed animal with a belly close to the ground...
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
inchwormInchworms are the caterpillars of geometer moths.Inchworm can also mean:*Inchworm , a song from the film Hans Christian Andersen*Inchworm , a ride-on toy manufactured by Hasbro in the 1970s...
, alternate between their front and back legs. An alternative to a gait which alternates between legs is hopping or saltation, where all legs move together. As a main means of locomotion, this is usually found in bipeds or semi-bipeds. Among the mammals saltation is commonly used among
macropodMacropods are marsupials belonging to the family Macropodidae, which includes kangaroos, wallabies, tree-kangaroos, pademelons, and several others. Before European settlement, there were about 53 species of Macropods. Six species have since become extinct. Another 11 species have been greatly...
s (
kangarooA kangaroo is a marsupial from the family Macropodidae . In common use the term is used to describe the largest species from this family, especially those of genus Macropus, Red Kangaroo, Antilopine Kangaroo, Eastern and Western Grey Kangaroo...
s and their relatives),
jerboaThe jerboa form the bulk of the membership of the family Dipodidae. Jerboas are jumping desert rodents found throughout Asia and Northern Africa.- Characteristics :...
s,
springhareThe springhare , or springhaas, is not actually a hare, but a member of the order Rodentia; it is the only species in its family Pedetidae and in the genus Pedetes. Synonyms are P. caffer or P...
s,
kangaroo ratKangaroo rats, genus Dipodomys, are small rodents native to North America. The common name derives from their bipedal form: as they hop in a manner similar to the much larger kangaroo, although they are not related.-Speciation:...
s, hopping mice,
gerbilA Gerbil is a small mammal of the order Rodentia. Once known simply as "desert rats", the gerbil subfamily includes about 110 species of African, Indian, and Asian rodents, including sand rats and jirds, all of which are adapted to arid habitats...
s, and
sportive lemurThe sportive lemurs are the medium sized primates that make up the Lepilemuridae family. The family consists of only one extant genus, Lepilemur, as well as the extinct genus Megaladapis. They are closely related to the other lemurs and exclusively live on the island of Madagascar...
s. Certain tendons in kangaroo hind legs are very
elasticIn physics, elasticity is the physical property of a material when it returns to its original shape after the stress under which it deforms is removed. The relative amount of deformation is called the strain.- Modelling elasticity :...
, allowing kangaroos to effectively bounce along conserving energy from hop to hop, making hopping a very energy efficient way to move around in their nutrient poor environment. Saltation is also used by many small birds.
FrogFrogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by long hind legs, a short body, webbed digits , protruding eyes and the absence of a tail...
s and
fleaFlea is the common name for insects of the order Siphonaptera which are wingless insects whose mouthparts are adapted for piercing skin and sucking blood....
s also hop.
Most animals move in the direction of their head. However there are some exceptions.
CrabCrabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax.Crabs have a soft body covered with a hard shell. They are generally covered with a thick exoskeleton, and armed with a...
s move sideways, and
naked mole ratThe naked mole rat , also known as the sand puppy, or desert mole rat is a burrowing rodent native to parts of East Africa and the only species currently classified in genus Heterocephalus...
s which live in tight tunnels underground can move backward or forward with equal facility.
CrayfishCrayfish, crawfish, or crawdads — members of the superfamilies Astacoidea and Parastacoidea — are freshwater crustaceans resembling small lobsters, to which they are related...
can move backward much faster than they can move forward.
Gait analysisGait analysis is the systematic study of animal locomotion, using the eye and the brain of observers, augmented by instrumentation for measuring body movements, body mechanics and the activity of the muscles. Gait analysis is used to assess, plan and treate individuals with conditions affecting...
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
transducerA transducer is a device, electrical, electronic, electro-mechanical, electromagnetic, photonic, or photovoltaic, that converts one type of energy or physical attribute to another for various purposes including measurement or information transfer .There are two kinds of transducers...
s (
strain gaugeA strain gauge is a device used to measure the strain of 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 a metallic foil pattern. The gauge is attached to the object by a suitable...
s). Skin
electrodeAn electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
s may also be used to measure
muscleMuscle is the contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
activity.
Limbless locomotion
There are a number of terrestrial and amphibious
limbless vertebratesMany vertebrates have evolved limbless forms. Reptiles have on a number of occasions evolved into limbless forms - snakes, amphisbaenia, and legless lizards...
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-bloodedA poikilotherm is an animal whose internal temperature varies along with that of the ambient environmental temperature. Most, but not all, ectotherms are poikilothermic...
groups; there are no
endothermicIn thermodynamics, the word endothermic "within-heating" describes a process or reaction that absorbs energy in the form of heat. Its etymology stems from the Greek prefix endo-, meaning “inside” and the Greek suffix –thermic, meaning “to heat”. The opposite of an endothermic process is an...
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
snakeSnakes are elongate legless carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic amniote vertebrates covered in overlapping scales...
s or
legless lizardLegless lizard may refer to any of several groups of lizards which have independently lost limbs or reduced them to the point of being of no use in locomotion. It is the common name for the family Pygopodidae, but often refers to other groups, such as limbless anguids, depending upon the region of...
s move on their smooth dry underside. Other animals have various features that aid movement. Molluscs such as
slugSlug is a common word, normally applied to any gastropod mollusc that lacks a shell, has a very reduced shell, or has a small internal shell, in contrast to snails, which are gastropods with coiled shells that are big enough to retract into. All slugs are descended from snails that gradually lost...
s and
snailThe word snail is a common name for almost all members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word snail is used in a general sense, it includes sea snails, land snails and freshwater snails. Snails lacking a shell or having only a very small one are...
s move on a layer of
mucusIn vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. It is a viscous colloid containing antiseptic enzymes and immunoglobulins that serves to protect epithelial cells in the respiratory,...
that is secreted from their underside, reducing friction and protecting from injury when moving over sharp objects.
EarthwormEarthworm is the common name for the largest members of Oligochaeta in the phylum Annelida. In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening posterior to the female pores, even though the internal male segments are anterior to the female...
s have small bristles (setae) that hook into the substrate and help them move. Some animals such as leeches 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
inchwormThe geometer moths or Geometridae are a family of the order Lepidoptera. A very large family, it has around 26,000 species of moths described . A well-known member is the Peppered Moth, Biston betularia, which has been subject of numerous studies in population genetics...
, also moves like this, clasping with appendages at either end of its body.
Limbless animals can also move using pedal locomotary waves, rippling the underside of the body. This is the main method used by molluscs such as slugs and snails, and also large flatworms, some other worms, and even
earless sealThe true seals or earless seals are one of the three main groups of mammals within the seal suborder, Pinnipedia. All true seals are members of the family Phocidae . They are sometimes called crawling seals to distinguish them from the fur seals and sea lions of the family Otariidae...
s. 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. Aquatic molluscs such as
limpetThe name Limpet is used for many kinds of mostly saltwater but also freshwater snails, specifically those that have a simple shell which is more or less broadly conical in shape, and which is either not coiled, or appears not to be coiled, in the adult snail.Thus the word "limpet" is an inexact...
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.
LugwormThe lugworm or sandworm is a large marine worm of the phylum Annelida. Its coiled castings are a familiar sight on a beach at low tide but the animal itself is not seen except by those who, from curiosity or to use as fishing bait, dig the worm out of the sand.-Overview:When fully grown, the...
s and seals also use direct waves.
Most snakes 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 locomotionRectilinear locomotion is a mode of locomotion most often associated with snakes, particularly heavy-bodied species like terrestrial pythons and boas, although most snakes are capable of it...
, 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
scuteA scute or scutum is a bony external plate or scale, as on the shell of a turtle, the skin of crocodilians, or the feet of some birds.-Properties:Scutes are similar to scales and serve the same function...
s 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 locomotionConcertina movement is the movement occurring in snakes and other legless organisms that consists of gripping or anchoring with portions of the body while pulling/pushing other sections in the direction of movement. Each point on the snake's body goes through alternating cycles of static contact...
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
sidewindingSidewinding is a type of locomotion unique to caenophidian snakes, used to move across loose or slippery substrates. It is most often used by the Saharan horned viper, Cerastes cerastes, and the sidewinder rattlesnake, Crotalus cerastes, to move across loose desert sands, but it is also used by...
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
wheelA wheel is a circular device that is capable of rotating on its axis, facilitating movement or transportation whilst supporting a load , or performing labour in machines. Common examples are found in transport applications. A wheel, together with an axle overcomes friction by facilitating motion by...
s for locomotion
(see
Rotation in living systemsRotating locomotion encompasses two distinct modes of locomotion: simple rolling, and spinning relative to a fixed axle or body, in the manner of a wheel or propeller...
), a small number of animals will move at times by
rolling their whole body.
Rolling animals can be divided into those which roll under the force of gravity and those which roll using their own power.
Gravity assisted
Web-toed salamander. This 10 cm long salamander lives on steep hills in the Sierra Nevada mountains. When it's disturbed or startled it coils itself up into a little ball often causing it to roll down hill (García-París & Deban 1995).
Namib wheeling spiders (
Carparachne 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 lays its eggs in a paralyzed spider so the larvae have enough food when they hatch. The spiders flip their body sideways and then cartwheel over their bent legs. The rotation is fast, with the golden wheel Spider (
Carparachne aureoflava) moving up to 20 revolutions per second, moving the spider at 1 metre per second. At this speed the spider appears only as a blurred ball. Video of a wheeling spider in the Namib can be found at . More videos of Namib wheeling spiders, showing wheeling and wasp/spider interactions can be found at . This spider was studied by Dr Joh Henschel of the Gobabeb Training & Research Centre.
PangolinA pangolin , also scaly anteater or trenggiling, is a mammal of the order Pholidota. There is only one extant family and one genus of pangolins, comprising eight species. There are also a number of extinct taxa. Pangolins have large keratin scales covering their skin and are the only mammals with...
s, a type of mammal covered in thick scales rolls into a tight ball when threatened. Pangolins has been reported to roll away from danger, by both gravity and self-powered methods. A pangolin in hill country in
SumatraSumatra is an island in western Indonesia, westernmost of the Sunda Islands. It is the largest island entirely in Indonesia , and the sixth largest island in the world .-Etymology:Sumatra was known in ancient times by the Sanskrit...
, in order to flee from the researcher, was observed to run to the edge of a slope and then curl into a ball and roll down the slope, crashing through the vegetation, and covering an estimated 30 metres or more in 10 seconds (Tenaza 1975).
Self-powered
CaterpillarCaterpillars are the larval form of a member of the order Lepidoptera . They are mostly phytophagous in food habit, with some species being entomophagous. Caterpillars are voracious feeders and many of them are considered pests in agriculture...
of the Mother-Of-Pearl Moth,
Pleuroptya ruralisThe Mother of Pearl is a species of moth of the family Crambidae. It is found in Europe. The species is notable for its rolling locomotion....
. This research was done by John Brackenbury at University of Cambridge in the United Kingdom. When attacked, this caterpillar will touch its head to its tail and roll backwards, up to 5 revolutions at about 40 cm per second, which is about 40 times its normal speed.
Nannosquilla decemspinosa, 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 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. Discovered in 1979 by Roy Caldwell, an animal behaviourist at the University of California at Berkeley
PangolinA pangolin , also scaly anteater or trenggiling, is a mammal of the order Pholidota. There is only one extant family and one genus of pangolins, comprising eight species. There are also a number of extinct taxa. Pangolins have large keratin scales covering their skin and are the only mammals with...
s have also been reported to roll away from danger by self-powered methods. Witnessed by a lion researcher in the
SerengetiThe Serengeti ecosystem is a geographical region located in north-western Tanzania and extends to south-western Kenya between latitudes 1 and 3 S and longitudes 34 and 36 E...
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 .
Limits and extremes
- The fastest terrestrial animal is the cheetah
The cheetah is an atypical member of the cat family that is unique in its speed, while lacking climbing abilities. The species is the only living member of the genus Acinonyx...
, which can attain maximal sprint speeds of approximately 104 km/h (64 miles/hour).
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