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Cotylorhynchus

Fossil specimen on display at the American Museum of Natural History

Reconstruction by Hirokazu Tokugawa

When: Permian (~299 to 265 million years ago)

Where: North America 

What: Cotylorhynchus is a member of one of the most basal groups of synapsids, the  Caseidae.  Cotylorhynchus was a herbivore, and reached lengths of up to 20 feet (~6 meters) long, with a massive barrel chest, putting weight estimates at around 2 tons. This animal is very large for its time… well at least its body is. Cotylorhynchus has one of the most extreme cases of ‘tiny head’ I have ever seen. Even more so than the sail-backed EdaphaosaurusWhich is closer to modern mammals than Cotylorhynchus is. It is one of the most primitive animals known that unambiguously falls on the synapsid lineage. It is so basal that it does not even have any differentiation seen in its dentition, though there are less teeth than found in the non synapsid contemporaries of this wee-headed creature.