Vytshegdosuchus

''Vytshegdosuchus'' is an extinct genus of paracrocodylomorph archosaur known from the Early Triassic (latest Olenekian stage) Yarenskian Gorizont of the Komi Republic of the European section of Russia. It contains a single species, ''Vytshegdosuchus zheshartensis''. ''Vytshegdosuchus'' was named by Andreii Sennikov in 1988.

Discovery

''Vytshegdosuchus'' is known from the holotype PIN 3361/134, a right ilium, and possibly from the paratype PIN 3361/127, a partial femur. These specimens were collected from the a fossil assemblage called the '' Parotosuchus'' fauna of the Upper Yarenskian Gorizont, in the Zheshart locality along the Vychegda River in Aikino district of the Komi Republic. A pterygoid and postcranial material from the Gam locality, a cervical vertebra (PIN 3369/139) from another locality and postcrania from the Mezhog locality were also assigned to ''Vytshegdosuchus'' by Sennikov (1999). Nesbitt (2009) argued that the specimens referred to ''Vytshegdosuchus'' cannot unambiguously be assigned to that taxon, as these localities are well separated, and the bones were found isolated. ''Vytshegdosuchus'' occurs with the erythrosuchian ''Garjainia'' and the possible proterosuchian ''Gamosaurus'' and demonstrates there was clear temporal overlap with paracrocodylomorph archosaurs and at least erythrosuchians as predicted earlier by phylogenetic analyses. A similar faunal assemblage is present in the Heshanggou Formation of China, which dates to the late Early and possibly early Middle Triassic, as evidenced by the cooccurrence of the basal erythrosuchian '' Fugusuchus'' and the poposauroid '' Xilousuchus''.

The holotype of ''Vytshegdosuchus'' is also the oldest material currently considered as belonging to Archosauria from Russia, and the only from the Early Triassic. Furthermore, a numerical phylogenetic analysis performed by Nesbitt (2011) placed it in the Paracrocodylomorpha. The Yarenskian Gorizont is generally considered late Olenekian in age on the basis of palynology and the presence of the characteristic Olenekian temnospondyl '' Parotosuchus''. ''Parotosuchus'' also occurs in Germany within three formations of the Middle Buntsandstein, and is therefore broadly of Olenekian age and considered an index taxon for these strata. ''Vytshegdosuchus'' is from the Gamskian, the upper biochron of the Yarenskian Gorizont and may therefore be latest Olenekian in age and approximately contemporaneous with the poposauroid '' Ctenosauriscus''.

Description

''Vytshegdosuchus'' was originally assigned to the Rauisuchidae based on comparisons with loricatans such as '' Rauisuchus'', '' Saurosuchus'' and '' Arganasuchus''. Gower and Sennikov (2000), who revised its diagnosis, focused on the holotype ilium. It preserved a thickened ridge dorsal to the supra-acetabular crest, which according to Nesbitt (2009) is a character only present in many paracrocodylomorphs. Although the anterior process curves medially at its anterior extent according to Sennikov (1988), a character which is not present in these paracrocodylomorphs, an ilium (SAM-PK-11753) from the Anisian-aged Lifua Member of the Manda Formation shows an identical feature. The femur assigned to ''Vytshegdosuchus'' is consistent with proterosuchids, ''Euparkeria'' and archosaurs since, according to Gower and Sennikov (2000), it has no intertrochanteric fossa and a low fourth trochanter. Furthermore, the femur has a groove on its proximal surface, a character state found in paracrocodylomorphs, as well as some dinosauriforms. The lack of distinct anteromedial tuber of the femur' proximal end is found in nearly all archosaurs ancestrally. Thus, both the ilium and the femur bear features only present in Archosauria, regardless of their association. Therefore, Nesbitt (2009) suggested that ''Vytshegdosuchus'' is an archosaur which is assignable to Paracrocodylomorpha.

References

{{Taxonbar, from=Q3335365

Paracrocodylomorpha
Early Triassic reptiles of Europe
Prehistoric pseudosuchian genera