LABYRINTHODONT

any member of an extinct order (Labyrinthodontia) or subclass of amphibians that constituted the dominant animals of Late Paleozoic and Triassic time (about 350 to 210 million years ago). Labyrinthodonts first appeared in the Late Devonian (374 to 360 million years ago) and may well have included the ancestors of all land vertebrates; some of them closely approached the reptiles in structure. Many were as large as alligators, some as small as salamanders. By the Permian Period (286 to 245 million years ago) certain genera had become terrestrial, but both the early members of the group and the late degenerate forms were aquatic. The body was stout and lizardlike, with short limbs. The large skull was solidly roofed (hence the term Stegocephalia, often applied to these and other early amphibians). The vertebrae, in contrast to those of most land vertebrates, had two parts.