9/9/2023 0 Comments Platypus walk sidewaysThe 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. With the exception of the birds, all terrestrial vertebrate groups are mostly quadrupedal - the mammals, the reptiles, and the amphibians usually move on four legs. They have thick muscular tails and when moving slowly may alternate between resting their weight on their tails and their two hind legs. Macropods such as kangaroos are the only example of tripedal movement. Also cockroaches and some lizards may run on their two hind legs. Only a few mammals such as humans and the giant pangolin commonly show an alternating bipedal gait. Most bipedal mammals move by hopping - the macropods and various jumping rodents. There are also a number of bipedal mammals. The group that is exclusively bipedal is the birds, which have an alternating gait. The best contender for unipedal movement is the springtail, which while typically 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.Ī fair number of species move and stand on two legs, that is, are bipedal. The number of locomotory appendages varies much between animals, and sometimes the same animal may use different numbers of its legs in different circumstances. For example, the mesozoic prehistoric crocodilian Erpetosuchus is believed to have had a fully erect stance and been terrestrial. 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). This is often linked with the evolution of endothermy (Bakker 1988). In these groups the legs are placed beneath the body. Among the invertebrates most arthropods, which includes the most diverse group of animals - the insects, many have a stance which might best be described as semi-erect.įinally there is the main form of stance of mammal and birds, the fully erect stance. A few mammals, such as the platypus also use this stance. It is also the main stance of the crocodilians. This mode of locomotion is found among some reptiles and amphibians. Here the legs are to the side, but the body is held above the substrate. The second form of stance found among legged terrestrial animals is the semi-erect stance. Among invertebrates there is anecdotal evidence that some octopus species (such as the Pinnoctopus genus), sometimes to pursue prey between rockpools, can also drag themselves across land a short distance by hauling its body along by it tentacles, see. Many reptiles and amphibians, some or all of the time, use this method of locomotion. Amphibious fish such as the mudskipper drag themselves across land on their sturdy fins. This is the earliest form of use of legs on land. Here the legs are used to drag the body over the land. Some animals may use different stances in different circumstances, depending on the stance's mechanical and energetic advantages. 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. The stance, the way the body is supported by the legs, is an important aspect. There are also many gaits, ways of moving the legs in order to locomote, such as walking, running, or hopping.Īppendages can be used for movement in a number of ways. Important aspects of legged locomotion are stance (the way the body is supported by the legs), the number of legs, and the functional structure of the leg and foot. 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.
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