Eryops megacephalus

Eryops /ˈɛəri.ɒps/ meaning "drawn-out face" because most of its skull was in front of its eyes (Greek ἐρύειν, eryein = drawn-out + ὤψ, ops = face) is a genus of extinct, amphibious temnospondyls. It contains the single species Eryops megacephalus, the fossils of which are found mainly in early Permian (about 295 million years ago) 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 averaged a little over 1.5–2.0 metres (4.9–6.6 ft) long and could
 grow up to 3 metres (9.8 ft), making them among the largest land
animals of their time. Adults weighed about 90 kilograms (200 lb). The
skull was proportionately large, being broad and flat and reaching
lengths of 60 centimetres (2.0 ft). It had an enormous mouth with many
curved teeth like the frog. Its teeth had enamel with a folded pattern, leading to its early classification as a "labyrinthodont"
 ("maze toothed"). The shape and cross section of Eryops teeth made them
 exceptionally strong and resistant to stresses. The palate, or roof of
 the mouth, contained three pairs of backward-curved fangs, and was
covered in backward-pointing bony projections which would have been used
 to trap slippery prey once caught. This, coupled with the wide gape,
suggest an inertial method of feeding, in which the animal would grasp
its prey and thrust forward, forcing the prey farther back into its
mouth.
The skeleton of Eryops was much more strongly built and
sturdy than related temnospondyls. The limbs were especially large and
strong. The pectoral girdle was highly developed, with a larger size for increased muscle
 attachments. Most notably, the shoulder girdle was disconnected from
the skull, resulting in improved terrestrial locomotion. The
crossopterygian cleithrum was retained as the clavicle, and the interclavicle
 was well-developed, lying on the underside of the chest. In primitive
forms, the two clavicles and the interclavicle could have grown
ventrally in such a way as to form a broad chest plate, although such
was not the case in Eryops. The upper portion of the girdle had a flat
scapular blade, with the glenoid cavity situated below performing as the articulation surface for the humerus, while ventrally there was a large flat coracoid plate turning in toward the midline.

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.