Phylogeny of the Amniota

Amniote groups are differentiated by the number and position of temporal openings in the skull. Relationships among the Anapsida (0 openings), Diapsida (2), and the extinct Synapsida (1 low) are uncertain: the absence of temporal openings in anapsids is sometimes considered to be the ancestral amniote condition. Therapsida are characterized by a Dentary-Squamosal jaw.