Chroniosuchia is a group of

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

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 ± 0. ...

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

in what is now

Kyrgyzstan Kyrgyzstan, officially the Kyrgyz Republic, is a landlocked country in Central Asia lying in the Tian Shan and Pamir Mountains, Pamir mountain ranges. Bishkek is the Capital city, capital and List of cities in Kyrgyzstan, largest city. Kyrgyz ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

and

Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

Eastern Europe Eastern Europe is a subregion of the Europe, European continent. As a largely ambiguous term, it has a wide range of geopolitical, geographical, ethnic, cultural and socio-economic connotations. Its eastern boundary is marked by the Ural Mountain ...

. 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

crocodile Crocodiles (family (biology), 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 more loosely to include ...

s. The group is traditionally considered to be a suborder or order of

labyrinthodont "Labyrinthodontia" (Greek, 'maze-toothed') is an informal grouping of extinct predatory amphibians which were major components of ecosystems in the late Paleozoic and early Mesozoic eras (about 390 to 150 million years ago). Traditionally conside ...

s. Chroniosuchians likely had ecological niches as riverside predators, and may have been outcompeted by semiaquatic true reptiles such as phytosaurs in the late

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

. Most forms bore a heavy armour of

scute A scute () or scutum (Latin: ''scutum''; plural: ''scuta'' "Scutum (shield), 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 Bird anatomy#Scales, birds. The ter ...

s 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'' 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 amph ...

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 Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

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. Tetrapod vertebrae

Chroniosuchians are distinguished from other early reptiliomorphs by the lack of

intertemporal bone The intertemporal bone is a paired Skull, cranial bone present in certain Sarcopterygii, sarcopterygians (lobe-finned fish) and extinct amphibian-Evolutionary grade, grade tetrapods. It lies in the rear part of the skull, behind the eyes. Many lin ...

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 Archosauriformes, archosauriforms, first appearing during the Triassic Period. Among Extant ...

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 defi ...

*Order Chroniosuchia **Family Bystrowianidae ***'' Axitectum'' ***'' Bystrowiana'' ***'' Bystrowiella'' ***'' Dromotectum'' ***'' Hassiacoscutum'' ***'' Jiyuanitectum'' ***'' Synesuchus'' **Family Chroniosuchidae ***'' Chroniosaurus'' ***'' Chroniosuchus'' ***'' Ingentidens'' ***'' Jarilinus'' ***'' Madygenerpeton'' ***'' 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

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

References

External links

* at Paleo

{{Taxonbar, from=Q677349 Permian tetrapods Triassic tetrapods Prehistoric tetrapod orders Guadalupian first appearances Late Triassic extinctions