Eryops megacephalus

Eryops meaning "drawn-out face" because most of its skull was in front of its eyes is a genus of extinct, amphibious temnospondyls. It contains the single species Eryops megacephalus, the fossils of which are found mainly in early Permian rocks of the Texas Red Beds, located in Archer County, Texas. Fossils have also been found in late Carboniferous period rocks from New Mexico. Several complete skeletons of Eryops have been found in lower Permian rocks, but skull bones and teeth are its most common fossils.

Eryops is currently thought to contain only one species, E. megacephalus, which means "large-headed Eryops". E. megacephalus fossils have been found only in rocks dated to the early Permian period (Sakmarian age, about 295 million years ago) in the southwestern United States, primarily in the Admiral Formation of the Texas Red Beds. During the mid-20th century, some older fossils were classified as a second species of Eryops, E. avinoffi. This species, known from Carboniferous period fossil found in Pennsylvania, had originally been classified in the genus Glaukerpeton. Beginning in the late 1950s, some scientists concluded that Glaukerpeton was too similar to Eyrops to deserve its own genus. However, later studies supported the original classification of Glaukerpeton, finding that it was more primitive than Eryops and some other early temnospondyls. Supposed Eryops fossils also found in older Pennsylvanian epoch rocks of the Conemaugh Group in West Virginia also turned out to be remains of Glaukerpeton. In 2005, a skull clearly belonging to Eryops was found in upper Pennsylvanian epoch rocks of the El Cobre Canyon Formation in New Mexico, representing the oldest known specimen.

Eryops were among the most formidable early Permian carnivores and perhaps the only ones capable of competing with the dominant synapsids of the time, though because they were semi-aquatic, if not mostly aquatic, as suggested by long bone microanatomy, they probably did not come into frequent competition with synapsids. Eryops lived in lowland habitats in and around ponds, streams, and rivers, and the arrangement and shape of their teeth suggests that they probably ate mostly large fish and aquatic tetrapods. The torso of Eryops was relatively stiff and the tail stout, which would have made them poor swimmers. While they probably fed on fish, adult Eryops must have spent most of their time on land. Like other large primitive temnospondyls, Eryops would have grown slowly and gradually from aquatic larvae, but they did not go through a dramatic metamorphosis like many modern amphibians. While adults probably lived in ponds and rivers, or may have ventured onto their banks, juvenile Eryops may have lived in swamps, which may have offered more shelter from predators.