Terrestrial locomotion
Terrestrial locomotion has evolved as animals adapted from aquatic to terrestrial environments. Locomotion on land raises different problems than that in water, with reduced friction being replaced by the increased effects of gravity.
As viewed from evolutionary taxonomy, there are three basic forms of animal locomotion in the terrestrial environment:
- legged – moving by using appendages
- limbless locomotion – moving without legs, primarily using the body itself as a propulsive structure.
- rolling – rotating the body over the substrate
Some
Aquatic animals adapted to
Many species of
Locomotion on irregular, steep surfaces require agility 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
The remainder of this article focuses on the
Legged locomotion
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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 vertebrates and the arthropods. 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. There are also many gaits, ways of moving the legs to locomote, such as walking, running, 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[1] 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 lizards. This posture is typically associated with trotting gaits, and the body flexes from side-to-side during movement to increase step length. All limbed reptiles and salamanders use this posture, as does the platypus and several species of frogs that walk. Unusual examples can be found among amphibious fish, such as the mudskipper, which drag themselves across land on their sturdy fins. Among the invertebrates, most arthropods – which includes the most diverse group of animals, the insects – have a stance best described as sprawling. There is also anecdotal evidence that some octopus 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)[2] – there may be video evidence of this.[3] 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 lizards and tegus.
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
A number of species move and stand on two legs, that is, they are
With the exception of the birds, terrestrial vertebrate groups with legs are mostly
Some species of invertebrate have even more legs, the unusual
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 tetrapods, the main group of terrestrial vertebrates (which also includes amphibious fish), have internal bones, with externally attached muscles for movement, and the basic form has three key joints: the shoulder joint, the knee joint, and the ankle joint, at which the foot 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. Also a few tetrapods, such as the macropods, have adapted their tails as additional locomotory appendages.
The fundamental form of the vertebrate
Among terrestrial
Gaits
Animals show a vast range of
Walking 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 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
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
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
Most animals move in the direction of their head. However, there are some exceptions.
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 transducers (strain gauges). Skin electrodes may also be used to measure muscle activity.
Limbless locomotion
There are a number of terrestrial and amphibious
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
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, also moves like this, clasping with appendages at either end of its body.
Limbless animals can also move using
Most
Rolling
Although animals have never evolved wheels for locomotion,[9][10] 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
The
Namib wheeling spiders (
Pangolins, 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, to flee from a 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 (100 ft) or more in 10 seconds.[16]
Self-powered
Pangolins have also been reported to roll away from danger by self-powered methods. Witnessed by a lion researcher[18] in the Serengeti 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
See also
References
- ^ Charig, A.J. (1972) The evolution of the archosaur pelvis and hind-limb: an explanation in functional terms. In Studies in Vertebrate Evolution (eds K.A. Joysey and T.S. Kemp). Oliver & Boyd, Edinburgh, pp. 121–55.
- ^ "TONMO.com Forums". Archived from the original on 2009-09-04. Retrieved 2008-08-03.
- ^ "NATURE. The Octopus Show". PBS. Retrieved 2008-08-03.
- ^ Bakker 1988
- ^ Reilly, Stephen M. and Elias, Jason A. 1998, Locomotion in alligator mississippiensis: kinematic effects of speed and posture and their relevance to the sprawling-to-erect paradigm, J. Exp. Biol. 201,2559-2574.
- ^ "Fossil of crocodile with erect stance found". Archived from the original on January 23, 2009. Retrieved 2009-03-31.
- ^ "Leg and foot". Archived from the original on 2008-04-04. Retrieved 2008-08-03.
- ISBN 978-1-56593-416-0. Retrieved 18 March 2015.
- S2CID 84618349.
- Sunday Times. Archived from the originalon February 21, 2007. Retrieved 2008-08-03.
- ^ García-París, M. & Deban, S. M. 1995. A novel antipredator mechanism in salamanders: rolling escape in Hydromantes platycephalus. Journal of Herpetology 29, 149-151.
- ^ a b c "Great Moments in Science - Real Wheel Animals - Part Two". Australian Broadcasting Corporation. 9 August 1999. Retrieved 2008-08-03.
- ^ Walker, Matt (15 October 2009). "Pebble toad's rock and roll life". BBC Earth News. Retrieved 24 February 2015.
- doi:10.1038/nmat1876. Abstract
- ^ Discover magazine: Beetle turns itself into a wheel 25 March 2011.
- JSTOR 1379632.
- ^ Pamela S. Turner. "Who You Callin' "Shrimp"?". 43 (6). National Wildlife. Archived from the original on 2007-03-14. Retrieved 2008-08-03.
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(help) - ^ "Serengeti - Smaller Night Animals". 2000-11-15. Retrieved 2008-08-03.
- ^ Prostak, Sergio (May 6, 2014). "Cebrennus rechenbergi: Cartwheeling Spider Discovered in Morocco". Sci-News.com. Retrieved 23 May 2015.
- .
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Bibliography
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