The osteology and systematic position of Dongusuchus efremovi Sennikov, 1988 from the Anisian (Middle Triassic) of Russia

Abstract

European Russia has yielded several fragmentary but potentially important archosauriform specimens from the Middle Triassic, but these have been only briefly described in the literature. One of these puzzling taxa is Dongusuchus efremovi Sennikov, 1988, described from the Donguz Svita. We present a redescription of Dongusuchus efremovi, which includes the first photographic atlas and thorough anatomical description of the holotype and referred specimens. This taxon is shown to be a gracile, probably fast-running species with elongate and slender limbs. A phylogenetic analysis recovers Dongusuchus efremovi as an early-diverging, non-archosaurian archosauriform. Previous work had suggested that this taxon was a ‘rauisuchid’. The gracile proportions of the femur and somewhat wedge-shaped head, however, are unusual for basal archosauriforms and are similar to the plesiomorphic state in crocodile and avian-line crown archosaurs. Several Early-Middle Triassic basal archosauriforms and early members of the crocodile and avian lineages were gracile with elongate, slender limbs. This suggests that the limb morphology of Dongusuchus efremovi may be plesiomorphic for Archosauria and proximal clades.

Keywords::

• Archosauromorpha
• Archosauriformes
• Archosauria
• Middle Triassic
• Donguz
• Russia

Acknowledgements

We thank Richard J. Butler (School of Geography, Earth and Environmental Sciences, University of Birmingham, United Kingdom) for comments, help with the phylogenetic analysis and critical discussion reagrding the material of Dongusuchusefremovi. We also thank Tomasz Sulej and Marian Dziewiński (Institute of Paleobiology, Polish Academy of Sciences, Warsaw) for discussion and preparation of photographs during our study of the Moscow collection and Magdalena Borsuk-Białynicka (Institute of Paleobiology, Polish Academy of Sciences, Warsaw) for discussions. We are grateful to Daniel Snitting (Uppsala University) for his grammatical improvements of an earlier version of the manuscript and Martin Ezcurra and anonymous reviewers for comments that improved this paper.

Additional information

Funding

Funding was provided by the Polish Ministry of Science and Higher Education [grant number 7986/B/P01/2011/40, grant of Tomasz Sulej and Grzegorz Niedźwiedzki]. Grzegorz Niedźwiedzki is currently funded by a grant awarded to Per E. Ahlberg (Uppsala University). Andrey Sennikov is partially supported by the Russian Foundation for Basic Research, projects number 13-05-00274, 14-04-00185, 14-05-93964, by Program of Basic Research of the Presidium of the Russian Academy of Sciences No. 28 ‘Problem of the origin of life and the formation of the biosphere’ and by the subsidy of the Russian Government to support the ‘Program of competitive growth of Kazan Federal University among world's leading academic centres’. Stephen L. Brusatte's trip to Russia was supported by an NSF DDIG [grant number NSF DEB 1110357].