Protosuchia is a group of extinct Mesozoic

crocodyliform Crocodyliformes is a clade of crurotarsan archosaurs, the group often traditionally referred to as "crocodilians". They are the first members of Crocodylomorpha to possess many of the features that define later relatives. They are the only pseudo ...

s. They were small in size (~1 meter in length) and

terrestrial Terrestrial refers to things related to land or the planet Earth. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on or near the ground, as opposed to ...

. In

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

terms, Protosuchia is considered an informal group because it is a

grade Grade most commonly refers to: * Grade (education), a measurement of a student's performance * Grade, the number of the year a student has reached in a given educational stage * Grade (slope), the steepness of a slope Grade or grading may also ref ...

of basal crocodyliforms, not a true

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

Classification

Recent phylogenetic analyses have not supported Protosuchia as a natural group. However, two studies found a clade of

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 ...

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...

animals:Pol D, Ji S-a, Clark JM, Chiappe LM. 2004. Basal crocodyliforms from the Lower Cretaceous Tugulu Group (Xinjiang, China), and the phylogenetic position of ''Edentosuchus''. ''Cretaceous Research'' 25: 603-622.Fiorelli LE, Calvo JO. 2007. The first "protosuchian" (Archosauria: Crocodyliformes) from the Cretaceous (Santonian) of Gondwana. ''Arquivos do Museu Nacional, Rio de Janeiro'' 65 (4): 417-459. *''

Edentosuchus ''Edentosuchus'' is a genus of protosuchian crocodylomorph. It is known from fossils found in rocks of the Early Cretaceous-age Tugulu Group from the Junggar Basin, Xinjiang, China. Two partial skulls and several neck vertebrae are known to ...

'' *''

Hemiprotosuchus ''Hemiprotosuchus'' is an extinct genus of protosuchid from the Late Triassic (Norian stage) Los Colorados Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina, South America. It was named by Argentinian paleontologist Jo ...

'' *''

Orthosuchus ''Orthosuchus'' (meaning "straight crocodile") is an extinct genus of protosuchian crocodyliform that lived during the Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series ( ...

'' *'' Protosuchus'' Both of these studies also found a

more closely related to '' Hsisosuchus'' and

Mesoeucrocodylia Mesoeucrocodylia is the clade that includes Eusuchia and crocodyliforms formerly placed in the paraphyletic group Mesosuchia. The group appeared during the Early Jurassic, and continues to the present day. Diagnosis It was long known that M ...

consisting of

Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

genera: *''

Neuquensuchus ''Neuquensuchus'' (meaning "Neuquén crocodile", referring to the city) is an extinct genus of crocodyliform from the Santonian-age Upper Cretaceous Bajo de la Carpa Formation of Neuquén Province, Argentina. The known remains were discovere ...

'' *''

Shantungosuchus ''Shantungosuchus'' is an extinct genus of Early Cretaceous crocodyliform found in China. It includes three species: ''Shantungosuchus chuhsienensis'' and ''S. brachycephalus'', which were both described by Yang Zhongjian – usually ref ...

'' *'' Sichuanosuchus'' *'' Zosuchus'' However, other possible protosuchians from the

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...

, the

Gobiosuchidae Gobiosuchidae is a family of Cretaceous crocodyliforms known from Mongolia and Spain. Genera Three genera are currently classified within Gobiosuchidae: ''Cassissuchus'', ''Gobiosuchus'', and ''Zaraasuchus''.Ángela D. Buscalioni (2017) The G ...

(''

Gobiosuchus ''Gobiosuchus'' ("Gobi esertcrocodile") was a gobiosuchid crocodyliform described in 1972 by Polish palaeontologist Halszka Osmólska. It hails from the Late Cretaceous (Early Campanian) of Bayn Dzak ( Djadokhta Formation), in the Gobi Desert ...

'' and ''

Zaraasuchus ''Zaraasuchus'' ("hedgehog crocodile") was a gobiosuchid crocodyliform described in 2004 by Diego Pol and Mark Norell. It was found in the Red Beds of Zos Canyon, in the Gobi Desert of Mongolia, thus making it Late Cretaceous in age. The type ...

''), have been found to be either intermediate between these two clades, or members of the ''Sichuanosuchus'' clade. There is also another family of

genera, the

Shartegosuchidae Shartegosuchidae is an extinct family of Late Jurassic and Early Cretaceous crocodylomorphs. The family is named after the Late Jurassic Shar Teeg Beds in southwestern Mongolia, from which most shartegosuchid remains have been found. Five genera ...

(e.g. ''

Kyasuchus ''Kyasuchus'' is an extinct genus of shartegosuchid crocodylomorph. Fossils have been found from the Ilek Formation outcropping in the Kemerovo Oblast of Russia, deposited during the Aptian and Albian stages of the Early Cretaceous. The localiti ...

'', ''

Shartegosuchus ''Shartegosuchus'' is a genus of protosuchian-grade crocodylomorph. It is known primarily from PIN 4174/2, the partial deformed skull and jaws of a juvenile. This specimen was discovered in ancient lake deposits of the Tithonian-age Upp ...

'' and ''

Nominosuchus ''Nominosuchus'' is a genus of protosuchian-grade crocodylomorph. It is known from several specimens discovered in ancient lake deposits of the Tithonian-age Upper Jurassic Tsagaantsav Formation, southwestern Mongolia. The type specimen is PIN& ...

''). Below is a

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...

from Fiorelli and Calvo (2007). Protosuchians are marked by the green bracket.

References

Terrestrial crocodylomorphs Triassic crocodylomorpha Jurassic crocodylomorphs Early Cretaceous crocodylomorphs Late Cretaceous crocodylomorphs Late Triassic first appearances Late Cretaceous extinctions Paraphyletic groups {{paleo-archosaur-stub