Parareptilia
Encyclopedia
Parareptilia is a subclass or clade
of reptile
s which is 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 turtle
s, 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 anapsids 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:
Laurin
and Reisz
1995 presented a different cladogram, in which Reptilia is divided into Parareptilia (now a formal taxon) and Eureptilia. Captorhinidae is transferred to Eureptilia, and Parareptilia includes both early anapsid reptiles and turtles, but not 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:
In contrast, Rieppel, 1994, 1995; Rieppel & deBraga, 1996; and deBraga & Rieppel, 1997 have argued that turtles are actually related to Sauropterygia
, and hence are diapsid
s. The diapsid affinities of turtles have been supported by molecular phylogenies (e.g.
Zardoya and Meyer
1998; Iwabe et al., 2004; Roos et al., 2007; Katsu et al., 2010). This would make Parareptilia a wholly extinct clade. However this hypothesis has not been accepted by all vertebrate paleontologists
, and Benton
2000, 2004, retained the traditional class Anapsida for the "parareptiles" and turtles.
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
of reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s which is 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 turtle
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s, 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
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
reptiles, as opposed to the rest of the reptiles or Eureptilia
Eureptilia
Eureptilia is one of the two major clades of the Sauropsida, the other being Anapsida . Eureptilia includes not only all Diapsids, but also a number of primitive Permo-Carboniferous forms previously classified under the Anapsida, in the old order "Cotylosauria".Primitive eureptilians were all...
("true reptiles").
The name fell into disuse until it was revived by cladistic
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
studies, to refer to anapsids that were thought unrelated to turtles. Gauthier
Jacques Gauthier
Jacques Armand Gauthier is a vertebrate paleontologist, comparative morphologist, and systematist, and one of the founders of the use of cladistics in biology....
et al. 1988 provided the first phylogenetic definitions for the names of many amniote
Amniote
The amniotes are a group of tetrapods that have a terrestrially adapted egg. They include synapsids and sauropsids , as well as their fossil ancestors. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes...
taxa, including Sauropsida
Sauropsida
Sauropsida is a group of amniotes that includes all existing reptiles and birds and their fossil ancestors, including the dinosaurs, the immediate ancestors of birds...
as the parent clade for Reptilia, and argued cladistically that captorhinids
Captorhinida
Captorhinida is a doubly paraphyletic grouping of early reptiles. Robert L. Carroll ranked it as an order in the subclass Anapsida, composed of the following suborders:...
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
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
and Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
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
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
was as follows:
Laurin
Michel Laurin
Michel Laurin is a Canadian vertebrate paleontologist specialising in the origin and phylogeny of tetrapods, comparative biology and paleobiology. As an undergraduate he worked in the laboratory of Robert L. Carroll, and took his doctor thesis on the osteology of seymouriamorphs under Robert R....
and Reisz
Robert R. Reisz
Robert Rafael Reisz is a Canadian paleontologist and specialist in the study of early amniote and tetrapod evolution.Robert Reisz was born August 27, 1947, in Oradea, Romania. He received his B.Sc. , M.Sc. and Ph.D. from McGill University as Robert L. Carroll’s first doctoral graduate...
1995 presented a different cladogram, in which Reptilia is divided into Parareptilia (now a formal taxon) and Eureptilia. Captorhinidae is transferred to Eureptilia, and Parareptilia includes both early anapsid reptiles and turtles, but not 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:
In contrast, Rieppel, 1994, 1995; Rieppel & deBraga, 1996; and deBraga & Rieppel, 1997 have argued that turtles are actually related to Sauropterygia
Sauropterygia
Sauropterygia were a group of very successful aquatic reptiles that flourished during the Mesozoic before they became extinct at the end of the era. They were united by a radical adaptation of their shoulder, designed to support powerful flipper strokes...
, and hence are diapsid
Diapsid
Diapsids are a group of reptiles that developed two holes in each side of their skulls, about 300 million years ago during the late Carboniferous period. Living diapsids are extremely diverse, and include all crocodiles, lizards, snakes, and tuatara...
s. The diapsid affinities of turtles have been supported by molecular phylogenies (e.g.
Zardoya and Meyer
Axel Meyer
Axel Meyer is an evolutionary biologist and a Professor of Zoology and Evolutionary Biology at the Universität Konstanz, Germany....
1998; Iwabe et al., 2004; Roos et al., 2007; Katsu et al., 2010). This would make Parareptilia a wholly extinct clade. However this hypothesis has not been accepted by all vertebrate paleontologists
Vertebrate paleontology
Vertebrate paleontology is a large subfield to paleontology seeking to discover the behavior, reproduction and appearance of extinct animals with vertebrae or a notochord, through the study of their fossilized remains...
, and Benton
Michael J. Benton
Michael J. Benton is a British paleontologist, a Fellow of the Royal Society of Edinburgh, and professor of vertebrate palaeontology in the Department of Earth Sciences at the University of Bristol....
2000, 2004, retained the traditional class Anapsida for the "parareptiles" and turtles.
External links
- Parareptilia
- re Reptilian Subclass Parareptilia? - Dinosaur Mailing List archives