The Caseidae were a widespread group of very primitive herbivorous synapsids, which appeared during the later early Permian and persisted until the late Middle Permian. Although ranging in size from 1 to 5 1/2 meters (3–18 feet) in body length, caseids were surprisingly conservative in their skeletal anatomy and body proportions. All were large animals with small heads and barrel-like bodies. Some, like Angelosaurus and Cotylorhynchus, which exceeded 4 meters in length and were the largest of the pelycosaurs, seemed to have played the same ecological role during the later part of the early Permian that the pareiasaurs, herbivorous dinocephalians, did during the Middle and Late Permian.