Turfanosuchus

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]

The premaxilla probably had five teeth, while the maxilla had at least 13. Preserved teeth were curved and finely serrated.[2] The nasal bones project over the side of the snout and form the upper border of the antorbital fossa. The frontal bones (which form the portion of the skull above the eye sockets) wedge into the nasals as a large, V-shaped suture. Both of these traits are also present in Gracilisuchus.[4] The shape of the jugal (cheek bone), on the other hand, is truly unique to Turfanosuchus. The portion of the jugal which rises behind the eye socket has a very wide base, and its surface is set inwards relative to the portion below the eye socket.[2] As with other diapsids, Turfanosuchus had a pair of openings at the rear portion of the skull known as temporal fenestra. The bone separating the two holes, the squamosal, had a lower branch which curved forwards to contact the jugal and divide the lower temporal fenestra into two separate holes, leaving three holes at the back of the skull in total. This trait is also known is rauisuchids such as Postosuchus. A similar situation is visible in other gracilisuchids, which have a broad contact between the jugal and the lower branch of the squamosal. However, they did not retain the upper portion of the lower temporal fenestra, leaving only a small, triangular remnant of the lower temporal fenestra under the squamosal-jugal contact.[4]

Preserved portions of the palate (roof of the mouth) were generally similar to Euparkeria. One particular similarity is the presence of teeth on the pterygoid bone. Traditionally, pterygoid teeth are considered to be absent in crown-archosaurs. Wu & Russell (2001) used this to justify classifying Turfanosuchus as a non-archosaur archosauriform.[2] However, more recently pterygoid teeth have been reported in crown-archosaurs such as Eoraptor, Eudimorphodon, Lewisuchus,[3] Eodromaeus, and Yonghesuchus.[4] Therefore, their presence in Turfanosuchus does not preclude its classification as a crown-archosaur. Another seemingly non-archosaurian trait reported in Turfanosuchus is the fact that its internal carotid arteries enter the braincase from below, rather than from the sides as in almost all other archosaurs (including Gracilisuchus and Yonghesuchus[4]). However, this trait is also known to occur in other crown-archosaurs like Arizonasaurus, Qianosuchus, and Silesaurus. Otherwise, the braincase is generally similar to other archosaurs.[3]

The lower jaw was slender, with an elliptical hole known as a mandibular fenestra. The toothed dentary bone had two rear prongs surrounding the mandibular fenestra. Unique to Turfanosuchus among gracilisuchids, the lower prong was much longer than the upper prong. This had the added effect of excluding the angular bone (which formed the rear lower edge of the jaw) from forming the lower border of the mandibular fenestra. The surangular, which forms the upper rear portion of the jaw (and the upper border of the mandibular fenestra), was large. Another autapomorphy of Turfanosuchus is how the outer surface of the surangular was highly concave.[4] There were at least 16 teeth in the lower jaw, and they were similar in shape to those of the upper jaw.[2]

A sculpture of Turfanosuchus dabanensis, on display at the Paleozoological Museum of China.

The vertebrae of Turfanosuchus were similar to those of Euparkeria and pseudosuchians, with concavities on their sides and neural spines with expanded tops. There were two sacral (hip) vertebrae, which connected to the ilium (upper plate of the hip) with large, fan-shaped sacral ribs. No intercentra were preserved, and the vertebrae lacked bevelled edges, but since the vertebrae were disarticulated and some euparkeriids retain intercentra while lacking bevelled edges, their absence in Turfanosuchus cannot be proven. The ilium was similar to that of Ticinosuchus, with a short forward projection, a much larger rear projection, and a large bony acetabulum (hip socket). The pubis (lower front plate of the hip) was moderate in length and also similar to that of Ticinosuchus. Osteoderms (bony plates) were initially reported as being absent, but later preparation revealed one. This osteoderm was broad, with a ridge on its upper surface culminating in a pointed front prong. A corresponding groove-like depression was present on the lower surface.[2]

The humerus (upper arm bone) had a deltopectoral crest which was poorly differentiated from the humeral head. The femur (thigh bone) was similar to that of Euparkeria and most pseudosuchians, but it lacked the offset femoral head and raised fourth trochanter of avemetatarsalians or early crocodylomorphs.[2] The calcaneum (heel bone) had many similarities with that of "crurotarsan" archosauriforms (i.e. ones with a crurotarsal ankle like phytosaurs and suchians). These include a hemicylindrical (barrel-shaped) condyle for the fibula (outer shin bone), a continuous facet between this condyle and the facet for the fourth distal tarsal (a minor ankle bone),[2] and a rear projection known as a calcaneal tuber which was wider than tall and had flared edges. Some of these characteristics were not considered to be present until a re-evalutation of the specimen in 2011.[3]