Diapsida The name formerly given to a subclass of reptiles whose skulls are of the diapsid type. Today that classification has been abandoned as the more primitive and more advanced forms are not clearly related to one another and the diapsids are divided into two subclasses: the more primitive Lepidosauria (the scaly reptiles), and the more advanced Archosauria (ruling reptiles). The earliest known diapsids date from the end of the Palaeozoic. They occur in southern Africa in Upper Permian and Lower Triassic rocks. Birds are closely related to the archosaurs, and although their skulls have only one temporal opening, this is apparently derived from the fusion of the two diapsid apertures.

Diapsida See DIAPSID.