Euryapsida

Euryapsida is a polyphyletic (unnatural, as the various members are not closely related) group of sauropsids that are distinguished by a single temporal fenestra, an opening behind the orbit, under which the post-orbital and squamosal bones articulate.

[3] Historically, a variety of reptiles with upper fenestrae, either alone or with a lower emargination, have been considered euryapsid or parapsid, and to have had their patterns of fenestration originate separately from those of diapsids.

Euryapsida was proposed by Edwin H. Colbert as a substitute for the earlier term Synaptosauria, originally created by Edward D. Cope for a taxon including sauropterygians, turtles and rhynchocephalians.

Baur removed the rhynchocephalians from Synaptosauria and Williston later resurrected the taxon, including only Sauropterygia (Nothosauria and Plesiosauria) and Placodontia in it.

[8][9] Some 21st century studies have found that ichthyosaurs, thalattosaurs and sauropterygians were close relatives, either as stem-archosaurs[2][10] or as stem-saurians.