Romeriida is a clade of reptiles that consists of diapsids and the extinct protorothyrididgenusPaleothyris, if not the entire family Protorothyrididae. It is phylogenetically defined by Laurin & Reisz (1995) as the last common ancestor of Paleothyris and diapsids, and all its descendants. It is named after Alfred Romer, a prominent vertebrate paleontologist of the twentieth century.
Protorothyridids were once placed in the family Romeriidae along with the captorhinidRomeria. Because Romeria is now considered to be a captorhinid, and Captorhinidae is placed outside of Romeriida, the genus is excluded from the clade. Protorothyridids were once the collective term for several romeriid genera of uncertain classification. However, more recent studies have proposed that Protorothyrididae is a paraphyletic taxon. Therefore, it is possible that many protorothyridids do not lie within the clade Romeriida.
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