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

Greek Greek may refer to: 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 of all kno ...

, for the area where the

type specimen In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...

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

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

archosaur Archosauria () or archosaurs () is a clade of diapsid sauropsid tetrapods, with birds and crocodilians being the only extant taxon, extant representatives. Although broadly classified as reptiles, which traditionally exclude birds, the cladistics ...

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 preserve ...

s have been found from the Donguz Formation outcropping on the banks of the Donguz River in the

Orenburg Oblast Orenburg Oblast (also Orenburzhye) is a federal subject of Russia (an oblast), mainly located in Eastern Europe. Its administrative center is the city of Orenburg. From 1938 to 1957, it bore the name Chkalov Oblast in honor of Valery Chkal ...

Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

. 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 (stratigraphy), stage or earliest geologic age, age of the Middle Triassic series (stratigraphy), series or geologic epoch, epoch and lasted from million years ago until million years ag ...

and early Ladinian stages of the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epoch (geology), epochs of the Triassic period (geology), period or the middle of three series (stratigraphy), series in which the Triassic system (stratigraphy), system is di ...

.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 rauisuchian with a long, sigmoidally curved neck, unlike the more typical robust short-necked rauisuchians that appear later in the

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 ...

. 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 (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

is unique, a similar shape is present in the femora of some phytosaurs. 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 (biology), isotype ...

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 Extinction, extinct genus of archosauriform reptile from the Triassic of South Africa. ''Euparkeria'' is close to the ancestry of Archosauria, the reptile gro ...

'' 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, from Ancient Greek ψεύδος (''pseúdos)'', meaning "false", and σούχος (''soúkhos''), meaning "crocodile" is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely relat ...

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 , 'red' and , 'crocodile') is an extinct genus of archosauriform reptiles from the early Triassic of South Africa. Remains have been found from the Cynognathus Assemblage Zone of the Beaufort Group in the Karoo of South ...

''. ''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 bird-line archosaurs.

References

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