Cotylorhynchus

Cotylorhynchus is an extinct genus of herbivorous caseid synapsids that lived during the late Lower Permian (Kungurian) and possibly the early Middle Permian (Roadian) in what is now Texas and Oklahoma in the United States. The large number of specimens found make it the best-known caseid. Like all large herbivorous caseids, Cotylorhynchus had a short snout sloping forward and very large external nares. The head was very small compared to the size of the body. The latter was massive, barrel-shaped, and ended with a long tail. The limbs were short and robust. The hands and feet had short, broad fingers with powerful claws. The barrel-shaped body must have housed large intestines, suggesting that the animal had to feed on a large quantity of plants of low nutritional value. Caseids are generally considered to be terrestrial, though a semi-aquatic lifestyle has been proposed by some authors. The genus Cotylorhynchus is represented by three species, the largest of which could reach more than 6 m in length. However, a study published in 2022 suggests that the genus may be paraphyletic, with two of the three species possibly belonging to separate genera. The genus name Cotylorhynchus comes from the Greek kotyle, cup, hollow, and rhynchos, beak, or snout. The genus was named so because of the nasal opening which is surrounded by a depressed, cup-shaped bony surface. The skull of Cotylorhynchus shows the typical caseid morphology with a forward sloping snout, very large nasal opening, a skull roof with numerous small depressions, and a very large pineal foramen. The latter is wider than long as in Ennatosaurus and thus differs from that of Euromycter which is subcircular. The number of teeth in the upper and lower jaws ranges from 16 to 20. In the upper jaw, the anterior teeth are long and slender, while those behind decrease in size posteriorly and are slightly spatulate. All the marginal teeth have their distal end slightly inclined towards the interior of the mouth and the top of their crown each have three small cuspules arranged longitudinally.