Araeoscelida

An order of Paleozoic diapsid reptiles including the families Petrolacosauridae and Araeoscelidae. Members of these families resemble primitive modern lizards, such as the green iguana, in size and most body proportions, but are distinguished by their elongate necks and distal limb elements. Petrolacosaurus, from the Upper Pennsylvanian of Kansas, is the earliest known diapsid. The skull shows well-developed upper and lateral temporal openings and a subor-bital fenestra that are characteristic of the diapsids.

The following derived features distinguish members of the Araeoscelida from other early diapsids: six to nine elongate neck vertebrae; a radius as long as the humerus and a tibia as long as the femur; expanded neural arches; posterior cervical and anterior dorsal neural spines with mamillary processes; a coracoid process; and enlarged lateral and distal pubic tubercles. In contrast to later diapsids, members of the Araeoscelida show no evidence of an impedance-matching middle ear. The stapes is massive, the quadrate is not emarginated for support of a tympanum, and there is no retroarticular process. See also Reptilia.