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Quadrupedalism is a form of locomotion where animals have four legs that are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four legs is said to be a quadruped (from Latin quattuor for "four", and pes , pedis for "foot").
Salamanders, caecilians and some frogs have one or two rows of teeth in both jaws, but some frogs (Rana spp.) lack teeth in the lower jaw, and toads (Bufo spp.) have no teeth. In many amphibians there are also vomerine teeth attached to a facial bone in the roof of the mouth. [144] Edible frog (Pelophylax esculentus) exhibiting cannibalism
The digestion system of cats begins with their sharp teeth and abrasive tongue papillae, which help them tear meat, which is most, if not all, of their diet. Cats naturally do not have a diet high in carbohydrates, and therefore, their saliva does not contain the enzyme amylase. [31]
By mid-Carboniferous times, the stem-tetrapods had radiated into two branches of true ("crown group") tetrapods, one ancestral to modern amphibians and the other ancestral to amniotes. Modern amphibians are most likely derived from the temnospondyls , a particularly diverse and long-lasting group of tetrapods.
Digitigrades include birds (what many see as bird's knees are actually ankles), cats, dogs, and many other mammals, but not plantigrades (such as humans) or unguligrades (such as horses). Digitigrades generally move more quickly than other animals Comparison of lower limb structure. From left to right: plantigrade, digitigrade and unguligrade.
In counting legs, this list follows the conventions adopted in the relevant literature. For example, millipedes with gonopods are listed by numbers that exclude leg pairs that become gonopods. [2] [3] [4] Animals have been selected so that each number from 0 to 55 leg pairs has one example listed.
Centipedes have one pair of legs per body segment, with typically around 50 legs, but some species have over 200. The terrestrial animals with the most legs are the millipedes. They have two pairs of legs per body segment, with common species having between 80 and 400 legs overall – with the rare species Illacme plenipes having up to 750 legs.
These two components are what remains following fusion between a larger set of bones. An additional inset tooth row with up to 20 teeth lies parallel to the main marginal tooth row of the jaw. [20] All but the most primitive caecilians have two sets of muscles for closing the jaw, compared with the single pair found in other amphibians.