Overview
Diapsids are a clade of sauropsids, distinguished from other reptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The earliest traditionally identified diapsids, the araeoscelidians, appeared about three hundred million years ago during the late Carboniferous period. All diapsids other than the most primitive ones in the clade Araeoscelidia are often placed into the clade Neodiapsida, which appeared during the following Permian. The diapsids are extremely diverse, and in a cladistic sense, include birds and all modern reptile groups, including turtles, which were historically thought to lie outside the group. Recent studies have questioned the relationship of Araeoscelidia to Neodiapsida, with cladistic analyses suggesting the diapsid condition of araeoscelidians was evolved independently of neodiapsids.