Cotylorhynchus romeri is a Caseid from early Permian North America.It was a large herbivore that measured up to 3 metres long (9.8 feet). and weighed up to one or one and a half tonnes. It was over a metre tall and most of its length was its barrel-shaped body and long heavy tail.
It was one of the largest caseids and probably the best known due to its large size and unique features. Probably the best known trait Cotylorhynchus has its is hugely disproportionally small head relative to the large size of its body. This may have come from having no predators or reducing the weight of its head so it could look for more predators for longer as it fed on the plants it would have been strangely evolved for eating. Its small head may have come from when herbivores dipped their neck and put their head right to the ground it would have been nearly blind to any approaching predators. Cotylorhynchus would have not had many predators but its small head may have made it browse from low hanging branches and this would have enabled it to see seeing as its small head clearly did not develop as a defense against predators, as this would in fact serve to make the predators job easier having such a small weak target. This would have put the Cotylorhynchus in more danger. It also would not have evolved as a way of competing against other males for territory because if the head-butted with their weight, as modern herbivores do then its skull would have been damaged.
Cotylorhynchus would have been one of the dominant herbivores of the early Triassic seeing its huge size and specially evolved ecology. It would have been a very slow walker because of its weight, sprawled gait and relatively short legs. It seems to have had little to no defenses against predators apart from its huge size. This might mean that it travelled in groups or herd which would have added more protection to its small target.