Eureptilia ("true reptiles") is one of the two major clades of the Sauropsida, the other being Anapsida (or Parareptilia). Eureptilia includes not only all Diapsids, but also a number of primitive Permo-Carboniferous forms previously classified under the Anapsida, in the old (no longer recognised) order "Cotylosauria".
Primitive eureptilians were all small, superficially lizard-like forms, that probably scurried through the Paleozoic undergrowth in search of insects. The diapsids are the only eureptilian clade to continue beyond the Permian Period. Eureptilia is defined by the skull having greatly reduced supraoccipital, tabular, and supratemporal bones that are no longer in contact with the postorbital.
Cladogram modified aftervLaurin and Reisz (1995):
Sauropsida |--Anapsida (=Parareptilia) `--Eureptilia |--Captorhinidae `--Romeriida |--Protorothyrididae `--Diapsida