Dongusuchus
| Dongusuchus | |
|---|---|
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Scientific classification 
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | †Aphanosauria |
| Genus: | †Dongusuchus Sennikov, 1988 |
| Type species | |
| †Dongusuchus efremovi Sennikov, 1988
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Dongusuchus (meaning Donguz River crocodile in Greek, for the area where the type specimen was found[1]) is an extinct genus of archosaur from the Middle Triassic of Russia.[2] It is currently regarded as an aphanosaur (an early-diverging relative of dinosaurs and pterosaurs).[3]
The only confirmed fossils of Dongusuchus are femora (thigh bones) from the Donguz Formation, outcropping on the banks of the Donguz River in the Orenburg Oblast. Other slender limb bones from the formation may belong to Dongusuchus as well, but this is only based in size and proximity. The Donguz Formation is also called the Eryosuchus Fauna, named after the capitosaurid amphibian Eryosuchus, the most common animal found there. It probably dates back to the Anisian or early Ladinian stages of the Middle Triassic.[4]
Classification
[edit]Sennikov (1988) and Gower and Sennikov (2000) suggested that Dongusuchus was a lightly-built rauisuchian with a long, sigmoidally curved (S-shaped) neck, unlike the more typical robust short-necked rauisuchians that appear later in the Triassic.[1][4]
Nesbitt (2009) argued that Dongusuchus most probably represents a non-archosaurian archosauriform. According to Nesbitt (2009), two aspects of the upper femur suggest that it is not a member of Archosauria: a poorly defined crista tibiofibularis and the lack of a distinct anteromedial tuber. Although Gower and Sennikov (2000) suggested that the distinct sigmoidal shape of Dongusuchus femur is unique, a similar shape is present in the femora of some phytosaurs. A paratype tibia (shin bone) was also found to be more closely related to Euparkeria and phytosaurs, on the basis of its convex and rounded distal surface. Additionally, the proximal surface ( upper end) of the tibia lacks a trait present in nearly all pseudosuchians, a depression on its lateral condyle (outer knob of the knee joint). Nesbitt assigned Dongusuchus to Archosauriformes on the basis of the following traits: its femur has a low fourth trochanter, and its distal condyles do not expand markedly beyond the shaft. These traits suggest that Dongusuchus was an archosauriform more derived than Erythrosuchus.[5]
Dongusuchus was also excluded from Archosauria by Niedźwiedzki et al. (2014)[2] and a new large cladistic analysis of archosauromorphs by Ezcurra (2016)[6] found Dongusuchus to be the sister taxon to the Indian Yarasuchus. Both Dongusuchus and Yarasuchus were recovered in a clade with Spondylosoma and Teleocrater by Nesbitt et al. (2017)[3] at the base of Avemetatarsalia. In other words, they would qualify as early bird-line archosaurs, more closely related to pterosaurs and dinosaurs (including birds) rather than crocodilians.
References
[edit]- ^ a b Sennikov, A. G. (1988) Novyye rauizukhidy iz triasa yevropeyskoy chasti SSSR. Paleontol. Zhurn. 1990 (2): 124-128 Moscow.
- ^ a b Niedźwiedzki, Grzegorz; Sennikov, Andrey; Brusatte, Stephen L. (2016). "The osteology and systematic position of Dongusuchus efremovi Sennikov, 1988 from the Anisian (Middle Triassic) of Russia". Historical Biology. 28 (4): 550–570. doi:10.1080/08912963.2014.992017. S2CID 85312134.
- ^ a b Nesbitt, S.J.; Butler, R.J.; Ezcurra, M.D.; Barrett, P.M.; Stocker, M.R.; Angielczyk, K.D.; Smith, R.M H.; Sidor, C.A.; Niedźwiedzki, G.; Sennikov, A.G.; Charig, A.J. (2017). "The earliest bird-line archosaurs and the assembly of the dinosaur body plan". Nature. 544 (7651): 484–487. Bibcode:2017Natur.544..484N. doi:10.1038/nature22037. PMID 28405026. S2CID 9095072.
{{cite journal}}: CS1 maint: url-status (link) - ^ a b 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
- ^ Sterling J. Nesbitt (2009). "The early evolution of archosaurs: Relationships and the origin of major clades". Columbia University (Open Access Dissertation): 1–632.
- ^ Ezcurra, Martín D. (2016). "The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms". PeerJ. 4 e1778. doi:10.7717/peerj.1778. PMC 4860341. PMID 27162705.
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