Cotylorhynchus was a very large mammal-like reptile, synapsid, that lived in the southern part of what is now North America during the Early Permian period and persisted until the late-Mid Permian (about 265 mya). Cotylorhynchus are the most well known of the synapsid clade Caseidae and are in the order Pelycosauria.
Cotylorhynchus was the largest terrestrial animal of their time. They were herbivores, and because of their enormous size, full-grown animal probably did not fear any of the carnivores.
They could grow to lengths of up to 6 m (20 feet) and could achieve weights of up to 2 tons.