Terrestrial locomotion
Locomotion on land raises different problems than that in water, with reduced friction being replaced by the increased effects of gravity.
The remainder of this article focuses on the anatomical and physiological distinctions involving terrestrial locomotion from the taxonomic perspective.
This posture is typically associated with trotting gaits, and the body flexes from side-to-side during movement to increase step length.
Unusual examples can be found among amphibious fish, such as the mudskipper, which drag themselves across land on their sturdy fins.
This is often linked with the evolution of endothermy, as it avoids Carrier's constraint and thus allows prolonged periods of activity.
For example, the mesozoic prehistoric crocodilian Erpetosuchus is believed to have had a fully erect stance and been terrestrial.
The best contender for unipedal movement is the springtail, which while normally hexapedal, hurls itself away from danger using its furcula, a tail-like forked rod that can be rapidly unfurled from the underside of its body.
In humans, alternating bipedalism is characterized by a bobbing motion, which is due to the utilization of gravity when falling forward.
The most diverse group of animals on earth, the insects, are included in a larger taxon known as hexapods, most of which are hexapedal, walking and standing on six legs.
Only ichthyosaurs evolved more than 5 digits within tetrapods, while their transition from land to water again (limb terminations were becoming flippers).
Most mammals, such as cats and dogs, are digitigrade, 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.
All animals that have prehensile front limbs are plantigrade, even if their ankle joint looks extended (squirrels are a good example).
The arthropod legs are jointed and supported by hard external armor, with the muscles attached to the internal surface of this exoskeleton.
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.
Animals show a vast range of gaits, the order that they place and lift their appendages in locomotion.
In an informal sense, running is considered to occur when at some points in the stride all feet are off the ground in a moment of suspension.
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.
This may involve videoing subjects with markers on particular anatomical landmarks and measuring the forces of their footfall using floor transducers (strain gauges).
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.
This is the main method used by molluscs such as slugs and snails, and also large flatworms, some other worms, and even earless seals.
Earthworms move by retrograde waves alternatively swelling and contracting down the length of their body, the swollen sections being held in place using setae.
Finally the caenophidian snakes use the fast and unusual method of movement known as sidewinding on sand or loose soil.
[11][12] The pebble toad (Oreophrynella nigra) lives atop tepui in the Guiana highlands of South America.
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.
[14] 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 (80 ft) and as fast as 11 km/h (3 m/s; 7 mph).
[15] Pangolins, a type of mammal covered in thick scales, roll into a tight ball when threatened.
[16] Caterpillars of the mother-of-pearl moth, Pleuroptya ruralis, when attacked, will touch their heads to their tails and roll backwards, up to 5 revolutions at about 40 centimetres per second (16 in/s), which is about 40 times its normal speed.
[12] 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.
[19] The fastest terrestrial animal is the cheetah, which can attain maximal sprint speeds of approximately 104 km/h (64 mph).
