Angelosaurus

Angelosaurus is an extinct genus of herbivorous caseid synapsids that lived during the late Lower Permian (Kungurian) and early Middle Permian (Roadian) in what is now Texas and Oklahoma in the United States. Like other herbivorous caseids, it had a small head, large barrel-shaped body, long tail, and massive limbs. Angelosaurus differs from other caseids by the extreme massiveness of its bones, particularly those of the limbs, which show a strong development of ridges, processes, and rugosities for the attachment of muscles and tendons. Relative to its body size, the limbs of Angelosaurus were shorter and wider than those of other caseids. The ungual phalanges looked more like hooves than claws. The few known cranial elements show that the skull was short and more robust than that of the other representatives of the group. Angelosaurus is also distinguished by its bulbous teeth with shorter and wider crowns than those of other caseids. Their morphology and the high rate of wear they exhibit suggests a diet quite different from that of other large herbivorous caseids, and must have been based on particularly tough plants. A study published in 2022 suggests that the genus may be paraphyletic, with Angelosaurus possibly only represented by its type species A. dolani. The name of the genus Angelosaurus refers to the San Angelo Formation in Texas, where this animal was first discovered. It is completed by saurus meaning lizard. Angelosaurus is only known from incomplete skeletons and isolated bones. The genus is represented by three species, the largest, Angelosaurus greeni, reaching a size comparable to that of Cotylorhynchus romeri. Angelosaurus romeri was the smallest species and A. dolani was of intermediate size. However, the difference in size is not a relevant taxonomic criterion because the number of known specimens is too limited to know the maximum size reached by each species. These three species differ essentially in characteristics of the humerus, femur, and pelvis, which are the only bones allowing comparisons.