amphibia



amphibia defined in 1951 year

amphibia - amphibia;
amphibia - A class of vertebrates. Represented now by three orders: frogs, toads (Anura); newts, salamanders (Urodela); tropical burrowing worm-like Apoda. In the course of evolution they were the first vertebrates to inhabit the land (late Devonian, about 370 million years ago), being descended immediately from fish (Choa-nichthyes). The early Amphibia were immediate ancestors of the reptiles which themselves gave rise to mammals and birds. Amphibia differ from fish in having the four pentadactyl legs typical of tetrapods, hip girdle jointed to the vertebral column at the sacrum, and an ear-drum connected to the inner ear by a rod of bone (columella auris), which crosses the middle-ear. They differ from reptiles in that fertilization is not accomplished by coition, and the eggs are unprotected by a shell and embryonic membranes. Consequently most Amphibia have to become temporarily aquatic for the purpose of reproduction. Fossil Amphibia are distinguished from fossil reptiles by, e.g. having a single vertebra concerned in the sacrum, instead of two. Modern Amphibia have diverged far from those which were ancestral to Reptilia, losing much of their bony skeleton.

near amphibia in Knolik


amoeboidhome
letter "A"
start from "AM"
amphidiploid

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