Casea

Illustration showing skull form above

The skull of Casea had a larger orbit and was relatively wide, with the bone being pitted and the teeth long and blunt. Their common features are enumerated by Olson and include a very short snout, proportionally very small skulls, a barrel shaped body and a reduced phalangeal formula. [6] The structure of the skull has no lower temporal arcade, along with many other characters of the skeleton that justifies a suborbital position. These specimens show a loose union of the squamosal with the quadrate.[3] The skull is anteriorly broad and posteriorly short relative to its length and is shallow dorsoventrally. The skull roof is deeper in the posterior portions because of a slight doming of the parietal bones and the angled ventral cheek margin.[6]

The posterior margin of the skull is slightly inclined anterodorsally, and the occipital bone follows this inclination, projecting slightly beyond the posterior margin of the skull. In dorsal view the outline of the skull roof is spade shaped with the cheek region wider than the skull table. The palate is broad and plate-like. Casea genus has a narrow interpterygoid vacuity that divides the posterior portions of the palate at the midline.[6] The jaw is dominated by a large dentary and a strong medially directed process off the articular bone is present at the level of the articular facets for the quadrate.[6]

Skeleton from above

Post cranial development includes the characters of the skeleton are larger part of a tail, the sacrum, two lumbar vertebrae, pelvis, and the complete hind legs. The ribs of the sacral vertebrae decrease in mediolateral length posteriorly so that the sacrum tapers posteriorly in dorsal view. [7] Caseidae is based on the absence of a ventral midline keel on the posterior presacral central, the presence of a well-developed internal trocater on the femur, and an adductor crest that extends diagonally across the femoral shaft almost to the lateral condyle of the femur. [7] Casea based on the presence of a greatly expanded, fan-shaped ilium with a flat contact to the sacrum. C. broilii based on the lack of any expansion of the proximal tibial head.[7]

Postcranial anatomy of C. broilii was first noted by Williston and he observed that the first two sacral ribs were the same size and that the ilium featured a greatly expanded anterior process and only a moderately expanded posterior one.[7] The cervical were shorter, the dorsal ribs enclosed an enormous torso. The caudal were long and the tail tapered gradually. The pectoral girdle was more gracile. The ilium was broad with a large anterior process. The limbs were more gracile, and the hind limbs were sprawling. The digits were much longer than the Etatarsals.

Casea represents one of the first large and highly successful herbivores among terrestrial reptiles.[12] Among vertebrates this feeding strategy can be subdivided into many categories, including folivory, frugivory, granivory but among early terrestrial vertebrates, it is feeding on leaves, stems, roots and rhizomes. Herbivorous use massive crushing dentition on the palate and mandibles.[6] Caseids belong to the most basal clade of synapside, the Caseasuria, which also includes the small carnivorous eothrydids. Caseids are some of the youngest pelycosaur synapsids that survived to co-exists with more derived therapsids synapsids.[6] In the case of Caseids, herbivory is indicated by the presence of a massive rib cage in the thoracic and dorsal regions, and the expanded trunk extends posteriorly to the pelvic girdle, with large ribs fused to the lumbar vertebrae. This suggests that this feeding strategy originated sometime between the late Pennsylvanian and the Early Permian.[6] Some Caseids show dental specializations, with leaf-like large serrations being present in the marginal dentition.[4]

The locomotion of Casea involves a three-vertebra sacrum in early synapsids and no apparent link to body size, we argue that this sacral anatomy was related to more efficient terrestrial locomotion than to increased weight bearing.[7] Selective pressures for weight-bearing or more efficient locomotory styles and increasingly terrestrial lifestyles may have promoted the repeated acquisition of three sacral vertebrae in Synapsida. [7] the development of the third sacral rib attachment to the pelvis in Synapsids may support this hypothesis. [7]