''Dongusuchus'' (meaning ''Donguz River crocodile'' in

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

, for the area where the

type specimen In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes th ...

was foundSennikov, A. G. (1988) Novyye rauizukhidy iz triasa yevropeyskoy chasti SSSR. ''Paleontol. Zhurn.'' 1990 (2): 124-128 Moscow.) is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of archosaur.

Fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s have been found from the

Donguz Formation The Donguz Formation, Donguz Svita, or Donguz Rocks (russian: Донгузские скалы) is a Middle Triassic geological formation that crops out on the right bank of Donguz River in Orenburg Oblast, Russia, across the settlement of Pervoma ...

outcropping on the banks of the Donguz River in the Orenburg Oblast of

Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eig ...

. They are associated with a fossil assemblage called the ''Eryosuchus'' Fauna, named after the capitosaurid '' Eryosuchus'', the most common organism found from the assemblage. The locality dates back to the

Anisian In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from million years ago until million years ago. The Anisian Age succeeds the Olenekian Age (part of the Lower Triassic ...

and early

Ladinian The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between Ma and ~237 Ma (million years ago). The Ladinian was preceded by the Anisian and succeeded by the Carnian (part of the Upper or Late Triassic ...

stages of the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma and ...

.Gower, D. J. and Sennikov, A. G. (2000). Early archosaurs from Russia. In M. J. Benton, E. N. Kurochkin, M. A. Shishkin, D. M. Unwin (eds.), ''The Age of Dinosaurs in Russia and Mongolia''. Cambridge University Press, Cambridge. pp. 140-159 Sennikov (1988) and Gower and Sennikov (2000) suggested that ''Dongusuchus'' was a gracile rausuchian with a long, sigmoidally curved neck, unlike the more typical robust short-necked rauisuchians that appear later in the

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 ...

. More recently, Nesbitt (2009) argued that ''Dongusuchus'' most probably represents a non- archosaurian archosauriform. According to Nesbitt (2009), the poorly-defined crista tibiofibularis and the absence of a distinct anteromedial tuber of the proximal portion of the thighbone in ''Dongusuchus'' suggest that it is not a member of Archosauria. Although Gower and Sennikov (2000) suggested that the distinct sigmoidal shape of ''Dongusuchus''

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates wit ...

is unique, a similar shape is present in the femora of some

phytosaur 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 ...

s. A

paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype nor a syntype). O ...

tibia was also found to be more closely related to ''

Euparkeria ''Euparkeria'' (; meaning "Parker's good animal", named in honor of W.K. Parker) is an extinct genus of archosauriform from the Middle Triassic of South Africa. It was a small reptile that lived between 245-230 million years ago, and was close to ...

'' and phytosaurs, on the basis of its convex and rounded distal surface. Additionally, the proximal surface of the tibia lacks a trait present in nearly all

pseudosuchia Pseudosuchia is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely related to crocodilians than to birds. Pseudosuchians are also informally known as "crocodilian-line archosaurs". Prior to ...

ns, a depression on its lateral condyle. Nesbitt assigned ''Dongusuchus'' to Archosauriformes on the basis of the following traits: its femur has a low fourth trochanter, and the distal condyles do not expand markedly beyond the shaft. These traits suggest that ''Dongusuchus'' was an archosauriform more derived than ''

Erythrosuchus ''Erythrosuchus'' (from el, ἐρυθρός , 'red' and el, σοῦχος , 'crocodile') is an extinct genus of archosauriform reptile from the Triassic of South Africa. Remains have been found from the Cynognathus Assemblage Zone of the Bea ...

''. ''Dongusuchus'' was also excluded from Archosauria by Niedźwiedzki et al. (2014) and a new large cladistic analysis of archosauromorphs by Ezcurra (2016) found ''Dongusuchus'' to be the

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to the Indian ''Yarasuchus''. Both ''Dongusuchus'' and ''Yarasuchus'' were recovered in a clade with ''Spondylosoma'' and ''Teleocrater'' by Nesbitt et al. (2017)Nesbitt SJ et al. 2017. The earliest bird-line archosaurs and the assembly of the dinosaur body plan. Nature. at the base of Avemetatarsalia, making them more closely related to bird-line archosaurs.

References

Prehistoric avemetatarsalians Anisian genera Middle Triassic reptiles of Europe Fossil taxa described in 1988 Taxa named by Andrey G. Sennikov {{paleo-archosaur-stub