Parareptilia

Parareptilia ("at the side of reptiles") is a subclass or clade of reptiles which are variously defined as an extinct group of primitive anapsids, or a more cladistically correct alternative to Anapsida. Whether the term is valid depends on the phylogenetic position of turtles, the relationships of which to other reptilian groups are still uncertain.

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").

The name fell into disuse until it was revived by cladistic studies, to refer to anapsida that were thought unrelated to turtles. Gauthier et al. 1988 provided the first phylogenetic definitions for the names of many amniote taxa, including Sauropsida as the parent clade for Reptilia, and argued cladistically that captorhinids and turtles were sister groups, constituting the clade Anapsida (in a much more limited context than the definition given by Romer in 1967). A name had to be found for various Permian and Triassic reptiles no longer included in the Anapsids, and "Parareptiles" was chosen. However, they did not feel confident enough to erect Parareptilia as a formal taxon. Their cladogram was as follows: --o AMNIOTA |-- Synapsida `--o Sauropsida |--o "parareptiles" | |-- Mesosauridae | `--+-- Procolophonidae |     `--+-- Millerettidae |         `-- Pareiasauria `--o Reptilia |---o Anapsida |  |-- Captorhinidae |  `-- Testudines `--o Romeriida |-- Protorothyrididae `-- Diapsida

Laurin and Reisz 1995 presented a different cladogram, in which the Reptilia are divided into Parareptilia (now a formal taxon) and Eureptilia. The Captorhinidae are transferred to the Eureptilia, and the Parareptilia includes both early Anapsid reptiles and turtles, but not the Captorhinidae and Protorothyrididae. The mesosaurs are placed outside both groups, as the sister taxon to the reptiles (but still sauropsids). The traditional taxon of Anapsida is rejected as paraphyletic. This gives the following:

--o AMNIOTA |-- Synapsida `--o Sauropsida |-- Mesosauridae `--o Reptilia |--o Parareptilia | |-- Millerettidae | `--+-- Pareiasauria |    `--+-- Procolophonidae |       `-- Testudines `--o Eureptilia |-- Captorhinidae `--o Romeriida |-- Protorothyrididae `-- Diapsida

In contrast, Rieppel, 1994, 1995; Rieppel & deBraga, 1996; and deBraga & Rieppel, 1997 have argued that turtles are actually related to Sauropterygia, and hence are diapsids. The diapsid affinities of turtles have also been supported by molecular phylogeny (e.g. Zardoya and Meyer 1998). If so, this would mean that the Parareptilia would become a wholly extinct clade. However this hypothesis is not very widely accepted among vertebrate paleontologists, and Benton 2000, 2004, retains the traditional class Anapsida for the "parareptiles" and turtles.