Polonosuchus

Polonosuchus is a genus of rauisuchid known from the late Triassic (Carnian age) of Poland. It was a huge predator about 5–6 metres in length and, like all rauisuchians, was equipped with a large head of long sharp teeth. The legs were placed almost underneath the body, unlike most reptiles, which would have made it quite fast and a powerful runner. The appearance was very similar to that of the more known Postosuchus, of North America, and shared with the latter the ecological niche of the apex predator.

It was described as Teratosaurus silesiacus in 2005 by Tomasz Sulej, and was transferred to the genus Polonosuchus by Brusatte et al. in 2009. However, it is still considered closely related to the remaining Teratosaurus species, Teratosaurus suevicus. In Polonosuchus, the rostromedial foramen is on the medial surface of the maxilla, and the foramina for replacement teeth are not connected by a dental groove but are set together in a straight line, unlike in Teratosaurus. It also had a larger first dental alveolus than Teratosaurus, no different in size from alveoli 2-4, shorter overall maxillae (165 mm as opposed to 245 mm), and a large ridge between the palatal process and the dental alveoli which is not present in Teratosaurus at all.

The holotype, and only known specimen, is fragmentary. From the skull are preserved both maxillae, premaxillae, nasals, prefrontals, palatines and quadrates, the left jugal, the right pterygoid, quadratojugal, surangular, articular, squamosal and lacrimal, and fragments of the dentary. There are also the first three cervical vertebrae, nine caudal vertebrae, some caudal scutes and fragments of cervical ribs.

The maxillae are tall and laterally compressed, forming most of the borders of the antorbital fenestra (visible on the photo above). The palatal process extends anteroventrally and is very short. A ridge extending to form a suture with the palatine is present above the sixth, seventh and eighth dental alveoli. Small infraorbital foramina are located around the edge of the antorbital fenestra, near the teeth. At least eleven dental alveoli were present, although the total is not certain as both maxillae are broken off at the posterior ends. Small replacement teeth are visible above some of the alveoli, indicating it was probably a polyphyodont.

The premaxillae are very similar to those of Postosuchus, but slightly smaller; the posterodorsal process is broken off, but sutures present on the nasal bones show it would have extended all the way up to the anterior border of the naris. The palatal processes of the premaxillae are incompletely preserved, but would almost certainly have articulated with those of the maxillae. There are certainly four alveoli present, with a small cavity which may be a fifth.

The nasals have a long dorsoventrally compressed process which would have extended down between the maxilla and premaxilla. They also have a long anterior process with a triangular cross-section. The surface for articulation with the lacrimal is clearly visible on the right nasal.

The lacrimal has a thick rugose ridge extending back from that on the nasal. Its lamellar part forms the posterodorsal border of the antorbital fenestra, and is articulated with the maxillae which form much of the rest of the borders. There is also a descending process of the lacrimal which forms most of the posterior border of the antorbital fenestra, with a noticeably striated ridge. This descending process would probably have contacted the jugal at its ventral end.

The prefrontals are large triangular plates which overhang the orbits, with rugose lateral surfaces. All the surfaces which articulate with the other bones of the skull roof are narrow and oblique.