All caseids, whether modest or enormous, are characterized by small cervical vertebrae, bulky, barrel-shaped bodies and relatively massive limbs.
 Although ranging in size from 1–5.5 metres (3 ft 3 in–18 ft 1 in) 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 long and were the largest of the pelycosaurs, may have been aquatic foragers, relying on their paddle-like limbs to swim.

Recent studies on caseid ribs suggest that the animals may have been aquatic, and possibly possessed a diaphragm to assist their breathing.
It was less efficient than that of their modern mammal relatives, being capable of limited costal ventilation.
It likely relied on support from the animal's abdominal musculature.
All caseids, whether modest or enormous, are characterized by small cervical vertebrae, bulky, barrel-shaped bodies and relatively massive limbs.  Although ranging in size from 1–5.5 metres (3 ft 3 in–18 ft 1 in) 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 long and were the largest of the pelycosaurs, may have been aquatic foragers, relying on their paddle-like limbs to swim.
Recent studies on caseid ribs suggest that the animals may have been aquatic, and possibly possessed a diaphragm to assist their breathing. It was less efficient than that of their modern mammal relatives, being capable of limited costal ventilation. It likely relied on support from the animal's abdominal musculature.
Caseidae