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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.
A tetrapod is any four-limbed vertebrate animal of the superclass Tetrapoda. Tetrapods include all extant and extinct amphibians and amniotes, with the latter in turn evolving into two major clades, the sauropsids and synapsids. Some tetrapods such as snakes, legless lizards, and caecilians had evolved to become limbless via mutations of the Hox gene, although some do still have a pair of vestigial spurs that are remnants of the hindlimbs.
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.
The Batrachia are a clade of amphibians that includes frogs and salamanders, but not caecilians nor the extinct allocaudates. The name Batrachia was first used by French zoologist Pierre André Latreille in 1800 to refer to frogs, but has more recently been defined in a phylogenetic sense as a node-based taxon that includes the last common ancestor of frogs and salamanders and all of its descendants. The idea that frogs and salamanders are more closely related to each other than either is to caecilians is strongly supported by morphological and molecular evidence; they are, for instance, the only vertebrates able to raise and lower their eyes. However, an alternative hypothesis exists in which salamanders and caecilians are each other's closest relatives as part of a clade called the Procera, with frogs positioned as the sister taxon of this group.
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.
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.
Neodiapsida is a clade, or major branch, of the reptilian family tree, typically defined as including all diapsids apart from some early primitive types known as the araeoscelidians. Modern reptiles and birds belong to the neodiapsid subclade Sauria.
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.
Coelurosauravus is an extinct genus of gliding reptile, known from the Late Permian of Madagascar. Like other members of the family Weigeltisauridae, members of this genus possessed long, rod-like ossifications projecting outwards from the body. These bony rods were not extensions of the ribs but were instead a feature unique to weigeltisaurids. It is believed that during life, these structures formed folding wings used for gliding flight, similar to living gliding Draco lizards.
Avicephala is a potentially polyphyletic grouping of extinct diapsid reptiles that lived during the Late Permian and Triassic periods characterised by superficially bird-like skulls and arboreal lifestyles. As a clade, Avicephala is defined as including the gliding weigeltisaurids and the arboreal drepanosaurs to the exclusion of other major diapsid groups. This relationship is not recovered in the majority of phylogenetic analyses of early diapsids and so Avicephala is typically regarded as an unnatural grouping. However, the clade was recovered again in 2021 in a redescription of Weigeltisaurus, raising the possibility that the clade may be valid after all.
Younginiformes is a group of diapsid reptiles known from the Permian-Triassic of Africa and Madagascar. It has been used as a replacement for "Eosuchia". Younginiformes were historically suggested to be lepidosauromorphs, but were later suggested to be basal non-saurian neodiapsids. The group is sometimes divided into two families, Tangasauridae and Younginidae. The monophyly of the group is disputed. A 2009 study found them to be an unresolved polytomy at the base of Neodiapsida, while a 2011 study recovered the group as paraphyletic. A 2022 study recovered the Younginiformes as a monophyletic group of basal neodiapsid reptiles, also including Claudiosaurus and Saurosternon as part of the group. Some younginiforms like Hovasaurus and Acerosodontosaurus are thought to have had an amphibious lifestyle, while others like Kenyasaurus, Thadeosaurus and Youngina were probably terrestrial.
Triadobatrachus is an extinct genus of salientian frog-like amphibians, including only one known species, Triadobatrachus massinoti. It is the oldest member of the frog lineage known, and an excellent example of a transitional fossil. It lived during the Early Triassic about 250 million years ago, in what is now Madagascar.
Claudiosaurus is an extinct genus of diapsid reptiles from the Late Permian Sakamena Formation of the Morondava Basin, Madagascar. It has been suggested to be semi-aquatic.
Hovasaurus is an extinct genus of basal diapsid reptile. It lived in what is now Madagascar during the Late Permian and Early Triassic, being a survivor of the Permian–Triassic extinction event and the paleontologically youngest member of the Tangasauridae. Fossils have been found in the Permian Lower and Triassic Middle Sakamena Formations of the Sakamena Group, where it is amongst the commonest fossils. Its morphology suggests an aquatic ecology.
Weigeltisaurus is an extinct genus of weigeltisaurid reptile from the Late Permian Kupferschiefer of Germany and Marl Slate of England. It has a single species, originally named as Palaechamaeleo jaekeli in 1930 and later assigned the name Weigeltisaurus jaekeli in 1939, when it was revealed that Palaeochamaeleo was a preoccupied name. A 1987 review by Evans and Haubold later lumped Weigeltisaurus jaekeli under Coelurosauravus as a second species of that genus. A 2015 reassessment of skull morphology study substantiated the validity of Weigeltisaurus and subsequent authors have used this genus. Like other Weigeltisaurids, they possessed long rod-like bones that radiated from the trunk that were likely used to support membranes used for gliding, similar to extant Draco lizards.
Drepanosaurs are a group of extinct reptiles that lived between the Carnian and Rhaetian stages of the late Triassic Period, approximately between 230 and 210 million years ago. The various species of drepanosaurid were characterized by specialized grasping limbs and often prehensile tails, adaptions for arboreal (tree-dwelling) and fossorial (digging) lifestyles, with some having also been suggested to be aquatic. Fossils of drepanosaurs have been found in Arizona, New Mexico, New Jersey, Utah, England, and northern Italy. The name is taken from the family's namesake genus Drepanosaurus, which means "sickle lizard," a reference to their strongly curved claws.
Acerosodontosaurus is an extinct genus of neodiapsid reptiles that lived during the Upper Permian of Madagascar. The only species of Acerosodontosaurus, A. piveteaui, is known from a natural mold of a single partial skeleton including a crushed skull and part of the body and limbs. The fossil was discovered in deposits of the Lower Sakamena Formation. Based on skeletal characteristics, it has been suggested that Acerosodontosaurus individuals were at least partially aquatic.
Weigeltisauridae is a family of gliding neodiapsid reptiles that lived during the Late Permian, between 259.51 and 251.9 million years ago. Fossils of weigeltisaurids have been found in Madagascar, Germany, Great Britain, and Russia. They are characterized by long, hollow rod-shaped bones extending from the torso that probably supported wing-like membranes. Similar membranes are also found in several other extinct reptiles such as kuehneosaurids and Mecistotrachelos, as well as living gliding lizards, although each group evolved these structures independently.
Protorosauria is an extinct, likely paraphyletic group of basal archosauromorph reptiles from the latest Middle Permian to the end of the Late Triassic of Asia, Europe and North America. It was named by the English anatomist and paleontologist Thomas Henry Huxley in 1871 as an order, originally to solely contain Protorosaurus. Other names which were once considered equivalent to Protorosauria include Prolacertiformes and Prolacertilia.
References
- ↑ Ascarrunz, Eduardo; Rage, Jean-Claude; Legreneur, Pierre; Laurin, Michel (14 June 2016). "Triadobatrachus massinoti, the earliest known lissamphibian (Vertebrata: Tetrapoda) re-examined by μCT scan, and the evolution of trunk length in batrachians". Contributions to Zoology. 85 (2): 201–234. doi: 10.1163/18759866-08502004 . ISSN 1875-9866.
- ↑ De Buffrénil, Vivian; Mazin, Jean‐Michel (1 September 1989). "Bone histology of claudiosaurus germaini (reptilia, claudiosauridae) and the problem of pachyostosis in aquatic tetrapods". Historical Biology. 2 (4): 311–322. doi:10.1080/08912968909386509. ISSN 0891-2963.
- ↑ EVANS, SUSAN E.; HAUBOLD, HARTMUT (1 July 1987). "A review of the Upper Permian genera Coelurosauravus, Weigeltisaurus and Gracilisaurus (Reptilia: Diapsida)". Zoological Journal of the Linnean Society. 90 (3): 275–303. doi:10.1111/j.1096-3642.1987.tb01356.x. ISSN 0024-4082.
- ↑ Frey, Eberhard; Sues, Hans-Dieter; Munk, Wolfgang (7 March 1997). "Gliding Mechanism in the Late Permian Reptile Coelurosauravus". Science. 275 (5305): 1450–1452. doi:10.1126/science.275.5305.1450.
- ↑ Buffa, Valentin; Frey, Eberhard; Steyer, J.-Sébastien; Laurin, Michel (4 March 2021). "A new cranial reconstruction of Coelurosauravus elivensis Piveteau, 1926 (Diapsida, Weigeltisauridae) and its implications on the paleoecology of the first gliding vertebrates". Journal of Vertebrate Paleontology. 41 (2): e1930020. doi:10.1080/02724634.2021.1930020. ISSN 0272-4634.
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