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Chroniosuchia is a group of
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 therapsid ...
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 in what is now Eastern Europe, Kyrgyzstan, China and Germany. Chroniosuchians are often thought to be reptiliomorphs, 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
crocodile Crocodiles (family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to include all extant mem ...
s. 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 equivalent g ...
in the late
Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
. Most forms bore a heavy armour of scutes along the back, possibly for protection against land born predators like therapsids, 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 con ...
'' suggests that it was amphibious to terrestrial.


Description

The most distinguishing features of chroniosuchians are the rows of interlocking bony plates called
osteoderm 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 (extinct amp ...
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 i ...
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 bone The Intertemporal bone is a paired cranial bone present in bony fish and certain extinct amphibian-grade tetrapods. It lies in the rear part of the skull, behind the eyes. Many lineages of four-limbed vertebrates ("tetrapods" in the broad sense) h ...
s 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, birds ...
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 hi ...
'' ***''
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 su ...
'' ***''
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 ...
'' ***''
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 ...
'' ***'' 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' ...
'' ***'' Synesuchus'' **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 con ...
'' ***'' Chroniosuchus'' ***'' Ingentidens'' ***'' Jarilinus'' ***'' Madygenerpeton'' ***'' Phratochronis'' ***'' Uralerpeton'' ***''
Suchonica ''Suchonica'' is an extinct genus of chroniosuchid reptiliomorph from upper Permian (upper Tatarian age) deposits of Sukhona Formation of Vologda Region, Russia. It was first named by V. K. Golubev in 1999 File:1999 Events Collage.png, F ...
'' *** ''
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

image:Bystrowiana permira1DB.jpg, '' Bystrowiana permira'' image:Chroniosaurus dong12DB.jpg, '' Chroniosaurus dongusensis'' image:Uralerpeton2DB.jpg, '' Uralerpeton tverdokhlebovae''


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