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The word amphibian is derived from the Ancient Greek term ἀμφίβιος (amphíbios), which means 'both kinds of life', ἀμφί meaning 'of both kinds' and βίος meaning 'life'. The term was initially used as a general adjective for animals that could live on land or in water, including seals and otters. [8]
Amphibamus is a genus of amphibamid temnospondyl amphibians from the Carboniferous (middle Pennsylvanian) of North America. [1] [2] [3] This animal is considered to have been close to the ancestry of modern amphibians. Its length was about 20 centimetres (7.9 in). [4]
The only amphibians to bear claws are the African clawed frogs. Claws evolved separately in the amphibian and amniote (reptiliomorph) line. [12] However, the hairy frog has claw analogues on its feet; the frog intentionally dislocates the tips of its fingers to unsheathe the sharp points of its last phalanges.
The feet are broad with short digits, usually four on the front feet and five on the rear. Salamanders do not have claws, and the shape of the foot varies according to the animal's habitat. Climbing species have elongated, square-tipped toes, while rock-dwellers have larger feet with short, blunt toes.
Little is known about the longevity of frogs and toads in the wild, but some can live for many years. Skeletochronology is a method of examining bones to determine age. Using this method, the ages of mountain yellow-legged frogs ( Rana muscosa ) were studied, the phalanges of the toes showing seasonal lines where growth slows in winter.
Eocaecilia, an Early Jurassic amphibian commonly considered one of the oldest (stem-group) caecilians. Little is known of the evolutionary history of the caecilians, which have left a very sparse fossil record. The first fossil, a vertebra dated to the Paleocene, was not discovered until 1972. [44]
The African clawed frog (Xenopus laevis), also known as simply xenopus, African clawed toad, African claw-toed frog or the platanna) is a species of African aquatic frog of the family Pipidae. Its name is derived from the short black claws on its feet. The word Xenopus means 'strange foot' and laevis means 'smooth'.
While reptiles and amphibians can be quite similar externally, the French zoologist Pierre André Latreille recognized the large physiological differences at the beginning of the 19th century and split the herptiles into two classes, giving the four familiar classes of tetrapods: amphibians, reptiles, birds and mammals.