Dongusuchus

Dongusuchus (meaning Donguz River crocodile in Greek, for the area where the type specimen was found) is an extinct genus of archosaur from the Middle Triassic of Russia. It is currently regarded as an aphanosaur (an early-diverging relative of dinosaurs and pterosaurs).

The only confirmed fossils of Dongusuchus are femora (thigh bones) from the Donguz Formation, outcropping on the banks of the Donguz River in Orenburg Oblast. Other slender limb bones from the formation may belong to Dongusuchus as well, but this is only based on 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.

Classification

Sennikov (1988) and Gower and Sennikov (2000) suggested that Dongusuchus was a lightly-built rauisuchian (an early relative of crocodilians) with a long, sigmoidally curved (S-shaped) neck, unlike the more typical robust short-necked rauisuchians that appear later in the Triassic.

Nesbitt (2009) argued that Dongusuchus most likely represents a non-archosaurian archosauriform (a reptile related to both dinosaurs and crocodilians, but originating prior to their last common ancestor). According to Nesbitt (2009), two aspects of the femur suggest that it is not a member of Archosauria: a poorly defined crista tibiofibularis (a ridge at the back of the knee) and the lack of a distinct anteromedial tuber (a knob near the hip joint). 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.