Turfanosuchus
Turfanosuchus is a genus of archosauriform reptile, likely a gracilisuchid archosaur, which lived during the Middle Triassic (Anisian) of northwestern China. The type species, T. dabanensis, was described by C.C. Young in 1973, based on a partially complete but disarticulated fossil skeleton (IVPP V.32237) found in the Kelamayi Formation of the Turfan Basin.[1]
Turfanosuchus had a peculiar combination of features which has made it difficult to classify in the past. It possessed teeth on the palate, and internal carotid arteries which entered the braincase from below. These two traits were rare among Archosauria (true, crown-group archosaurs) and are more similar to non-archosaurian archosauriforms like Euparkeria.[2] On the other hand, the ankle was much more advanced than that of animals like Euparkeria, and some features of the skull have only been observed in true archosaurs, particularly early suchians (distant ancestors of modern crocodilians).[3] Out of this group, Turfanosuchus shares the most similarities with Gracilisuchus and Yonghesuchus, and a 2014 study grouped these three genera in the family Gracilisuchidae. Gracilisuchidae lies within Pseudosuchia, which contains all archosaurs more closely related to crocodilians than to birds. Some skull features previously considered unique to Turfanosuchus are now considered to characterize Gracilisuchidae, but Turfanosuchus retains a few unique features of the jaw and cheek region.[4]
The skull of Turfanosuchus was proportionally similar to that of other small generalized archosauriforms such as Euparkeria and Gracilisuchus. The premaxilla (a toothed bone at the tip of the snout) projects a small prong behind the nares (nostril holes). This prong, known as a posterodorsal process, bisects a corresponding branch of the nasal bones (which formed the upper surface of the snout).[2] As with other archosaurs and their relatives, the side of the snout has a hole (known as an antorbital fenestra) surrounded by a lowered basin of bone (known as an antorbital fossa). The maxilla (the main toothed bone of the snout) also had a posterodorsal process, a much more rare trait compared to the posterodorsal process of the premaxilla (which was present in most archosauromorphs). The maxilla's posterodorsal process was a small, triangular peak of bone which formed the lower rear corner of the antorbital fossa and connected to the lacrimal bone (which lies between the antorbital fossa and the eye socket).[4]
These posterodorsal processes are very characteristic, either by bisecting the nasal (in the case of the premaxilla's) or existing in the first place (in the case of the maxilla's). As such, they were considered by Wu & Russell (2001) to be autapomorphies (unique distinguishing traits) of Turfanosuchus.[2] However, they are now both known to be present in Yonghesuchus and (to a lesser extent) Gracilisuchus, so they likely diagnose the entire family Gracilisuchidae,[4] or possibly even larger subsets of Archosauria. For example, the premaxillary posterodorsal process of Revueltosaurus also bisects its nasal, and a posterodorsal process of the maxilla is present in some aetosaurs and poposauroids.[3]
