The name Parareptilia was coined by
Olson in 1947 to refer to an extinct group of
Paleozoic reptiles, as opposed to the rest of the reptiles or
Eureptilia ("true reptiles"). Olsen's term was generally ignored, and various taxa later known as "parareptiles" were generally not placed into exclusive groups with each other. Many were classified as "cotylosaurs" (a
wastebasket taxon of stout-bodied "primitive" reptiles or reptile-like tetrapods) or "
anapsids" (reptiles without
temporal fenestrae, such as modern turtles). Parareptilia's usage was revived by
cladistic studies, to refer to those traditional "anapsids" that were thought to be unrelated to turtles.
Gauthier et al. (1988) provided the first
phylogenetic definitions for the names of many
amniote taxa and argued that
captorhinids and turtles were sister groups, constituting the clade Anapsida (in a much more limited context than typically applied). A name had to be found for a clade of various early-diversing
Permian and
Triassic reptiles no longer included in the anapsids. Olsen's term "parareptiles" was chosen to refer to this clade, although its instability within their analysis meant that Gauthier et al. (1988) were not confident enough to erect Parareptilia as a formal taxon. Their
cladogram is as follows: }}
Laurin &
Reisz (1995) found a slightly different topology, in which Reptilia is divided into Parareptilia and Eureptilia. They argued that Testudines (turtles) were members of Parareptilia; in fact, they explicitly defined Parareptilia as "Testudines and all amniotes more closely related to them than to diapsids". Captorhinidae was transferred to Eureptilia, while Parareptilia included turtles alongside many of the taxa named as such by Gauthier et al. (1988). There was one major exception: mesosaurs were placed outside both groups, as the sister taxon to the
crown group Reptilia. Mesosaurs were still considered sauropsids, as they were closer to reptiles than to synapsids. The traditional group "Anapsida" was rejected as a
paraphyletic assemblage. The cladogram of Laurin & Reisz (1995) is provided below: }} In contrast, several studies in the mid-to-late 1990s by
Olivier Rieppel and
Michael deBraga argued that turtles were actually
lepidosauromorph diapsids related to the
sauropterygians. The diapsid affinities of turtles have been supported by
molecular phylogenies. The first genome-wide phylogenetic analysis was completed by Wang et al. (2013). Using the draft genomes of
Chelonia mydas and
Pelodiscus sinensis, the team used the largest turtle data set to date in their analysis and concluded that turtles are likely a sister group of crocodilians and birds (Archosauria). This placement within the diapsids suggests that the turtle lineage lost diapsid skull characteristics, since turtles possess an anapsid skull. This would make Parareptilia a totally extinct group with skull features that resemble those of turtles through
convergent evolution. With turtles positioned outside of "parareptiles", Tsuji and Müller (2009) redefined Parareptilia as "the most inclusive clade containing
Milleretta rubidgei and
Procolophon trigoniceps, but not
Captorhinus aguti." }} A 2020 study by David P. Ford and Roger B. J. Benson found that Parareptilia was nested within Diapsida as the sister group to
Neodiapsida, with the clade containing Neodiapsida and Parareptilia dubbed Neoreptilia, which suggests that "parareptiles" were ancestrally diapsid. This excluded
mesosaurs, which were again found to be basal among the sauropsids. More recent studies support this hypothesis, instead finding anatomical evidence placing millerettid "parareptiles" as sister to Neodiapsida, forming the clade
Parapleurota. Cladogram after Jenkins et al. (2025), with traditional "parareptiles" highlighted in orange: }} }} }} }} }} }} }} }} }} }} }} }} }} }} }} }} }} }} == Evolutionary history ==