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Chroniosuchia is a group of
Chroniosuchians are distinguished from other early reptiliomorphs by the lack of intertemporal bones in the skull, as well as the presence of holes in front of the eye sockets called
image:Bystrowiana permira1DB.jpg, '' Bystrowiana permira''
image:Chroniosaurus dong12DB.jpg, '' Chroniosaurus dongusensis''
image:Uralerpeton2DB.jpg, '' Uralerpeton tverdokhlebovae''
{{Taxonbar, from=Q677349 Permian tetrapods Triassic tetrapods Prehistoric animal orders Guadalupian first appearances Late Triassic extinctions
tetrapod
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...
s that lived from the Middle Permian
The Guadalupian is the second and middle series/ epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ± ...
to Late Triassic
The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...
in what is now Eastern Europe
Eastern Europe is a subregion of the European continent. As a largely ambiguous term, it has a wide range of geopolitical, geographical, ethnic, cultural, and socio-economic connotations. The vast majority of the region is covered by Russia, whic ...
, Kyrgyzstan
Kyrgyzstan,, pronounced or the Kyrgyz Republic, is a landlocked country in Central Asia. Kyrgyzstan is bordered by Kazakhstan to the north, Uzbekistan to the west, Tajikistan to the south, and the People's Republic of China to the ea ...
, China and Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
. Chroniosuchians are often thought to be reptiliomorph
Reptiliomorpha (meaning reptile-shaped; in PhyloCode known as ''Pan-Amniota'') 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 defi ...
s, but some recent phylogenetic analyses suggest instead that they are stem-tetrapods. They were all rather short limbed with a strong tail and elongated snout, somewhat resembling modern crocodiles. The group is traditionally considered to be a suborder or order of labyrinthodonts. Chroniosuchians likely had ecological niches as riverside predators, and may have been outcompeted by semiaquatic true reptiles such as phytosaurs
Phytosaurs (Φυτόσαυροι in greek) are an extinct group of large, mostly semiaquatic Late Triassic archosauriform reptiles. Phytosaurs belong to the order Phytosauria. Phytosauria and Phytosauridae are often considered to be equivalen ...
in the late Triassic
The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...
. Most forms bore a heavy armour of scute
A scute or scutum (Latin: ''scutum''; plural: ''scuta'' "shield") is a bony external plate or scale overlaid with horn, as on the shell of a turtle, the skin of crocodilians, and the feet of birds. The term is also used to describe the anterior po ...
s along the back, possibly for protection against land born predators like therapsid
Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...
s, or to strengthen the axial skeleton for terrestrial locomotion. Indeed, femoral microanatomy of ''Chroniosaurus
''Chroniosaurus'' is an extinct genus of chroniosuchid reptiliomorph from upper Permian (upper Tatarian age) deposits of Novgorod, Orenburg and Vologda Regions, Russia. It was first named by Tverdokhlebova in 1972
Within the cont ...
'' suggests that it was amphibious to terrestrial.
Description
The most distinguishing features of chroniosuchians are the rows of interlocking bony plates calledosteoderm
Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinc ...
s that run along their backs from head to tail. They are the most commonly found remains of chroniosuchians. Each osteoderm is paired with a single vertebra. The osteoderms are flat plates connected to the neural arch
The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
es of vertebra by an extension of bone on their undersurfaces. The front margin of each osteoderm has a pair of "anterior wings" that slip into a notch in the posterior margin of the osteoderm in front of it.
Chroniosuchians are distinguished from other early reptiliomorphs by the lack of intertemporal bones in the skull, as well as the presence of holes in front of the eye sockets called antorbital fenestra
An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with archosauriforms, first appearing during the Triassic Period. Among extant archosaurs, bird ...
e. Like many early tetrapods, chroniosuchians have vertebrae that are divided into three parts: a pleurocentrum and an intercentrum on the bottom, and a neural arch on top. Chroniosuchians have shizomerous vertebrae, meaning that the pleurocentrum makes up most of the body of the vertebra while the intercentrum is small and wedge-like.
Classification
Taxonomy
*Reptiliomorpha
Reptiliomorpha (meaning reptile-shaped; in PhyloCode known as ''Pan-Amniota'') 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 def ...
*Order Chroniosuchia
**Family Bystrowianidae
***''Axitectum
''Axitectum'' is an extinct genus of bystrowianid reptiliomorph from lower Triassic deposits of Nizhni Novgorod and Kirov Regions, Russia. It was a rather large animal judging by the size of its vertebrae. The back was covered in bands of high ...
''
***''Bystrowiana
''Bystrowiana'' is an extinct genus of bystrowianid chroniosuchian from upper Permian deposits of Vladimir Region, Russia and Jiyuan, China. Chroniosuchians are often thought to be reptiliomorphs, but some recent phylogenetic analyses sugges ...
''
***''Bystrowiella
''Bystrowiella'' is an extinct genus of bystrowianid reptiliomorph from upper Middle Triassic (Ladinian age) deposits of Kupferzell and Vellberg, northern Baden-Württemberg, Germany. It was first named by Florian Witzmann, Rainer R. Schoch and ...
''
***''Dromotectum
''Dromotectum'' is an extinct genus of bystrowianid reptiliomorph from the Late Permian of China and Early Triassic of Russia. Two species have been named: the type species ''D. spinosum'' and the species ''D. largum''. ''D. spinosum'', the fir ...
''
***'' Hassiacoscutum''
***''Jiyuanitectum
''Jiyuanitectum'' is an extinct genus of chroniosuchian tetrapod from the Late Permian Shangshihezi Formation of China. It is known from a single bony scute from Jiyuan in Henan province, ascribed to the type species ''Jiyuanitectum flatum'' in ...
''
***''Synesuchus
''Synesuchus'' is an extinct genus of bystrowianid reptiliomorph from middle Triassic (Ladinian stage) deposits of Komi Republic, northern Fore-Ural of Russia. It is known from the holotype PIN 4466/12, which consists of armor scute and from th ...
''
**Family Chroniosuchidae
***''Chroniosaurus
''Chroniosaurus'' is an extinct genus of chroniosuchid reptiliomorph from upper Permian (upper Tatarian age) deposits of Novgorod, Orenburg and Vologda Regions, Russia. It was first named by Tverdokhlebova in 1972
Within the cont ...
''
***'' Chroniosuchus''
***'' Ingentidens''
***'' Jarilinus''
***''Madygenerpeton
''Madygenerpeton'' is an extinct genus of chroniosuchid reptiliomorph from middle and upper Triassic deposits of Madygen Formation of Kyrgyzstan. It was first named by paleontologists Rainer R. Schoch, Sebastian Voigt and Michael Buchwitz in 201 ...
''
***'' Phratochronis''
***'' Uralerpeton''
***'' Suchonica''
*** ''Laosuchus
''Laosuchus'' is an extinct genus of chroniosuchian known from the Permian-Triassic boundary of Asia. Two species have been named.
Discovery
''L. naga'' was found in the Luang Prabang Basin of Northern Laos, part of the Indochina block. The s ...
''
Phylogeny
Below is the cladogram showing the preferred phylogeny of Buchwitz ''et al.'' (2012):Gallery
See also
*Permian tetrapods Permian tetrapods were amphibians and reptiles that lived during the Permian Period.
During this time, amphibians remained common, including various Temnospondyli and Lepospondyli. Synapsids became the dominant type of animal, represented by the ...
References
External links
* at Paleo{{Taxonbar, from=Q677349 Permian tetrapods Triassic tetrapods Prehistoric animal orders Guadalupian first appearances Late Triassic extinctions