Bipedal Animals
The great majority of living terrestrial vertebrates are quadrupeds. Among mammals, bipedalism is a normal method of ground locomotion in various groups of primates (e.g. lemurs, gibbons and Hominina), in the macropods (kangaroos, wallabies, etc.), and in a few groups of rodents, including kangaroo rats, gerbils and spring hares. All birds are bipeds when on the ground, a feature inherited from their dinosaur ancestors. Bipedalism evolved more than once in archosaurs, the group that includes both dinosaurs and crocodilians. Many species of lizards become bipedal during high-speed, sprint locomotion, including the world's fastest lizard, the spiny-tailed iguana (genus Ctenosaura). There are no known living or fossil bipedal amphibians.
Most bipedal animals move with their backs close to horizontal, using a long tail to balance the weight of their bodies. The primate version of bipedalism is unusual because the back is close to upright (completely upright in humans).
Humans, gibbons and large birds walk by raising one foot at a time. On the other hand most macropods, smaller birds, lemurs and bipedal rodents move by hopping on both legs simultaneously. Tree kangaroos are able to utilize either form of locomotion, most commonly alternating feet when moving arboreally and hopping on both feet simultaneously when on the ground.
Read more about this topic: Bipedalism
Famous quotes containing the word animals:
“You never see animals going through the absurd and often horrible fooleries of magic and religion.... Dogs do not ritually urinate in the hope of persuading heaven to do the same and send down rain. Asses do not bray a liturgy to cloudless skies. Nor do cats attempt, by abstinence from cat’s meat, to wheedle the feline spirits into benevolence. Only man behaves with such gratuitous folly. It is the price he has to pay for being intelligent but not, as yet, quite intelligent enough.”
—Aldous Huxley (1894–1963)