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An anapsid is an amniote whose skull lacks one or more skull openings near the temples. Traditionally, the Anapsida are the most primitive subclass of amniotes, the ancestral stock from which Synapsida and Diapsida evolved, making anapsids paraphyletic. It is however doubtful that all anapsids lack temporal fenestra as a primitive trait, and that all the groups traditionally seen as anapsids truly lacked fenestra.
Amniotes are a clade of tetrapod vertebrates that comprises sauropsids and synapsids. They are distinguished from the other tetrapod clade — the amphibians — by the development of three extraembryonic membranes, thicker and more keratinized skin, and costal respiration.
Sauria is the clade containing the most recent common ancestor of archosaurs and lepidosaurs, and all its descendants. Since most molecular phylogenies recover turtles as more closely related to archosaurs than to lepidosaurs as part of Archelosauria, Sauria can be considered the crown group of diapsids, or reptiles in general. Depending on the systematics, Sauria includes all modern reptiles or most of them as well as various extinct groups.
Diapsids are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The group first appeared about three hundred million years ago during the late Carboniferous period. All diapsids other than the most primitive ones in the clade Araeoscelidia are sometimes placed into the clade Neodiapsida. The diapsids are extremely diverse, and include birds and all modern reptile groups, including turtles, which were historically thought to lie outside the group. Although some diapsids have lost either one hole (lizards), or both holes, or have a heavily restructured skull, they are still classified as diapsids based on their ancestry. At least 17,084 species of diapsid animals are extant: 9,159 birds, and 7,925 snakes, lizards, tuatara, turtles, and crocodiles.
Sauropsida is a clade of amniotes, broadly equivalent to the class Reptilia. Sauropsida is the sister taxon to Synapsida, the other clade of amniotes which includes mammals as its only modern representatives. Although early synapsids have historically been referred to as "mammal-like reptiles", all synapsids are more closely related to mammals than to any modern reptile. Sauropsids, on the other hand, include all amniotes more closely related to modern reptiles than to mammals. This includes Aves (birds), which are now recognized as a subgroup of archosaurian reptiles despite originally being named as a separate class in Linnaean taxonomy.
The International Code of Phylogenetic Nomenclature, known as the PhyloCode for short, is a formal set of rules governing phylogenetic nomenclature. Its current version is specifically designed to regulate the naming of clades, leaving the governance of species names up to the rank-based nomenclature codes.
Archosauria is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term, which includes birds. Extinct archosaurs include non-avian dinosaurs, pterosaurs, and extinct relatives of crocodilians. Modern paleontologists define Archosauria as a crown group that includes the most recent common ancestor of living birds and crocodilians, and all of its descendants. The base of Archosauria splits into two clades: Pseudosuchia, which includes crocodilians and their extinct relatives, and Avemetatarsalia, which includes birds and their extinct relatives.
Mesosaurs were a group of small aquatic reptiles that lived during the early Permian period (Cisuralian), roughly 299 to 270 million years ago. Mesosaurs were the first known aquatic reptiles, having apparently returned to an aquatic lifestyle from more terrestrial ancestors. It is uncertain which and how many terrestrial traits these ancestors displayed; recent research cannot establish with confidence if the first amniotes were fully terrestrial, or only amphibious. Most authors consider mesosaurs to have been aquatic, although adult animals may have been amphibious, rather than completely aquatic, as indicated by their moderate skeletal adaptations to a semiaquatic lifestyle. Similarly, their affinities are uncertain; they may have been among the most basal sauropsids or among the most basal parareptiles.
Archosauriformes is a clade of diapsid reptiles that developed from archosauromorph ancestors some time in the Latest Permian. It was defined by Jacques Gauthier (1994) as the clade stemming from the last common ancestor of Proterosuchidae and Archosauria ; Phil Senter (2005) defined it as the most exclusive clade containing Proterosuchus and Archosauria.
Archosauromorpha is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs rather than lepidosaurs. Archosauromorphs first appeared during the late Middle Permian or Late Permian, though they became much more common and diverse during the Triassic period.
Reptiliomorpha is a clade containing the amniotes and those tetrapods that share a more recent common ancestor with amniotes than with living amphibians (lissamphibians). It was defined by Michel Laurin (2001) and Vallin and Laurin (2004) as the largest clade that includes Homo sapiens, but not Ascaphus truei. Laurin and Reisz (2020) defined Pan-Amniota as the largest total clade containing Homo sapiens, but not Pipa pipa, Caecilia tentaculata, and Siren lacertina.
Anthracosauria is an order of extinct reptile-like amphibians that flourished during the Carboniferous and early Permian periods, although precisely which species are included depends on one's definition of the taxon. "Anthracosauria" is sometimes used to refer to all tetrapods more closely related to amniotes such as reptiles, mammals, and birds, than to lissamphibians such as frogs and salamanders. An equivalent term to this definition would be Reptiliomorpha. Anthracosauria has also been used to refer to a smaller group of large, crocodilian-like aquatic tetrapods also known as embolomeres.
Pareiasaurs are an extinct clade of large, herbivorous parareptiles. Members of the group were armoured with osteoderms which covered large areas of the body. They first appeared in southern Pangea during the Middle Permian, before becoming globally distributed during the Late Permian. Pareiasaurs were the largest reptiles of the Permian, reaching sizes equivalent to those of contemporary therapsids. Pareiasaurs became extinct at the end of the Permian during the Permian-Triassic extinction event.
A grade is a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit.
The Procolophonia are a suborder of herbivorous reptiles that lived from the Middle Permian till the end of the Triassic period. They were originally included as a suborder of the Cotylosauria but are now considered a clade of Parareptilia. They are closely related to other generally lizard-like Permian reptiles such as the Millerettidae, Bolosauridae, Acleistorhinidae, and Lanthanosuchidae, all of which are included under the Anapsida or "Parareptiles".
Thecodontia, now considered an obsolete taxonomic grouping, was formerly used to describe a diverse "order" of early archosaurian reptiles that first appeared in the latest Permian period and flourished until the end of the Triassic period. All of them were built somewhat like crocodiles but with shorter skulls, more erect pose and usually somewhat lighter. The group includes the ancestors of dinosaurs, pterosaurs, and crocodilians, as well as a number of extinct forms that did not give rise to any descendants. The term thecodont is still used as an anatomical description of the tooth morphology seen in these species and others.
Varanoidea is a superfamily of lizards, including the well-known family Varanidae. Also included in the Varanoidea are the Lanthanotidae, and the extinct Palaeovaranidae.
Phylogenetic nomenclature is a method of nomenclature for taxa in biology that uses phylogenetic definitions for taxon names as explained below. This contrasts with the traditional approach, in which taxon names are defined by a type, which can be a specimen or a taxon of lower rank, and a description in words. Phylogenetic nomenclature is currently regulated by the International Code of Phylogenetic Nomenclature (PhyloCode).
Reptiles arose about 320 million years ago during the Carboniferous period. Reptiles, in the traditional sense of the term, are defined as animals that have scales or scutes, lay land-based hard-shelled eggs, and possess ectothermic metabolisms. So defined, the group is paraphyletic, excluding endothermic animals like birds that are descended from early traditionally-defined reptiles. A definition in accordance with phylogenetic nomenclature, which rejects paraphyletic groups, includes birds while excluding mammals and their synapsid ancestors. So defined, Reptilia is identical to Sauropsida.
Kevin de Queiroz is a vertebrate, evolutionary, and systematic biologist. He has worked in the phylogenetics and evolutionary biology of squamate reptiles, the development of a unified species concept and of a phylogenetic approach to biological nomenclature, and the philosophy of systematic biology.
References
- Estes, R.; de Queiroz, K. & Gauthier, Jacques (1988): Phylogenetic relationships within Squamata. In:Estes, R. & Pregill, G. (eds.): The Phylogenetic Relationships of the Lizard Families: 15–98. Stanford University Press, Palo Alto.
- Gauthier, Jacques A. (1982): Fossil xenosaurid and anguid lizards from the early Eocene of Wyoming, and a revision of the Anguioidea. Contributions to Geology, University of Wyoming21: 7-54.
- Gauthier, Jacques A. (1984): A cladistic analysis of the higher systematic categories of the Diapsida. [PhD dissertation]. Available from University Microfilms International, Ann Arbor, #85-12825, vii + 564 pp.
- Gauthier, J. A. (1986), "Saurischian monophyly and the origin of birds", in Padian, K. (ed.), The Origin of Birds and the Evolution of Flight, The Origin of Birds and the Evolution of Flight. Memoirs of the California Academy of Sciences, vol. 8, California Academy of Sciences, pp. 1–55, ISBN 0-940228-14-9
{{citation}}: External link in|series= - Gauthier, Jacques A.; Estes, R. & de Queiroz, Kevin (1988): A phylogenetic analysis of Lepidosauromorpha. In:Estes, R. & Pregill, G. (eds.): The Phylogenetic Relationships of the Lizard Families: 15–98. Stanford University Press, Palo Alto.
- Gauthier, J. A.; Kluge, A. G.; Rowe, T. (June 1988). "Amniote phylogeny and the importance of fossils" (PDF). Cladistics . John Wiley & Sons. 4 (2): 105–209. doi:10.1111/j.1096-0031.1988.tb00514.x. hdl: 2027.42/73857 . S2CID 83502693.
- Rowe, T. & Gauthier, Jacques (1990): Ceratosauria. In:Weishample, D.; Dodson, P. & Osmólska, Halszka (eds.): The Dinosauria: 151–168. University of California Press, Berkeley.
- de Queiroz, Kevin & Gauthier, Jacques A. (1992): Phylogenetic taxonomy. Annu. Rev. Ecol. Syst. 23: 449–480.
- Gauthier, Jacques A. (1994): The diversification of the amniotes. In:Prothero, D. (ed.): Major Features of Vertebrate Evolution: Short Courses in Paleontology: 129–159. Paleontological Society.
- Donoghue, M. J.; Gauthier, Jacques A. (June 2004). "Implementing the PhyloCode" (PDF). Trends Ecol. Evol. 19 (6): 281–282. doi:10.1016/j.tree.2004.04.004. PMID 16701272. Archived from the original (PDF) on 2011-04-01. Retrieved 2010-09-26.
