Bergisuchus

Bergisuchus is an extinct genus of small sebecosuchian mesoeucrocodylian known primarily from the Eocene Messel Pit in Germany. Few fossils of Bergisuchus have been discovered, only a single incomplete snout, a few partial lower jaws and some teeth. Despite being fragmentary, the jaw bones are enough to indicate that Bergisuchus had a short, deep, narrow snout and serrated teeth, quite unlike the broad flat snouts of modern crocodylians. As with other sebecosuchians, it is likely that Bergisuchus was a fast, terrestrial predator and not an aquatic ambush hunter like modern crocodylians. Its presence in Europe is also unusual, as later sebecosuchians were restricted entirely to South America, and so Bergisuchus indicates the group was once much more widespread in the early Cenozoic. Bergisuchus was first discovered by Dr. Dietrich Berg from the german Messel Pit in 1966, who originally classified it as an unnamed new species of sebecosuchian with close affinities to Sebecus, notable for being the first sebecosuchian remains to be recognised outside South America. It was named and described two years later in 1968 by German palaeontologist Oskar Kuhn, who named the binomial Bergisuchus dietrichbergi in honour of Dr. Berg and combined it with the Greek suffix suchos for 'crocodile'. Bergisuchus is known from the holotype snout and lower jaw (HLMD-Me 7003) from the Messel Pit near Darmstadt first reported in 1966, dated to the Mammal Paleogene zone (MP) 11, and an additional incomplete pair of mandibles (GM XVIII-49) from the Geiseltal open-pit coal mine near Halle in the state of Saxony-Anhalt from the slightly younger MP 12. The holotype is stored in the Hessisches Landesmuseum Darmstadt, while the paratype is housed in the Geiseltal Collection of the Center for Natural Science Collections at the Martin Luther University of Halle-Wittenberg, in Germany. In 2015, osteoderms from karst deposits dated to the Middle Eocene in Lissieu, France, were tentatively suggested to belong to Bergisuchus sp., or alternatively to Iberosuchus sp. (another European sebecosuchian). This referral was based on the similarity between the osteoderms and those of Baurusuchus and other sebecosuchians, as the two genera are the only known European sebecosuchians. Bergisuchus is only represented by the holotype snout and lower jaw (HLMD-Me 7003) and the referred pair of lower jaws (GM XVIII-49), so much of its anatomy is unknown. The snout is tall and laterally compressed, unlike the broad flat snouts of modern crocodylians, with tall nasals that form a raised, sharp midline along the length of the snout. Rossmann and colleagues reconstructed the incomplete premaxillae as tall and steep based on the dimensions of the maxilla, more similar in shape to those of Baurusuchus, Barinasuchus and Bretesuchus than to Sebecus. The premaxilla may also have sloped downwards, similar to that of Bretesuchus. Overall, the snout is relatively short and deep compared to the long, low skull of Sebecus. A deep notch is present between the maxilla and premaxilla to house the large lower canine tooth, along with a prominent bulge of bone above each. Based on the shape of the known snout, it's likely that Bergisuchus had separate nostril openings that faced laterally on the surface, as well as laterally facing eyes, unlike modern crocodylians. Also, it shares with Iberosuchus the unusual presence of a small antorbital fenestra, a feature that's invariably absent in both baurusuchids and sebecids. The surface of the maxilla is profusely sculpted with ridges and grooves, a feature that clearly distinguishes it from Iberosuchus. The lower jaws are mostly only known from incomplete dentaries (as well as part of the splenial), and their surfaces are as similarly strongly sculpted as the upper jaws. The teeth are relatively narrow and serrated (ziphodont), similar to those of predatory theropod dinosaurs and unlike the conical teeth of modern crocodylians. Few teeth themselves are preserved, but they include a very large and prominent serrated 'pseudocanine' that fits into the notch of the upper jaw. This canine is approximately 2 cm tall, and sits on a prominently raised portion of the jaw bone, which arches down in front and behind it and so the rest of the jaw is quite shallow. The rest of the teeth are mostly missing, but the size and shape of the remaining alveoli indicate the size and position of the other teeth in the jaws. The other teeth are around 3 times smaller in diameter than the canines, a unique characteristic of this genus, and are closely packed behind the canine in the lower jaw. Three small teeth are present in front of the canine, the first of which is larger and procumbent, facing up and forwards at the front of the jaw. The maxillary teeth are similarly small, the largest being the third tooth, and the rest of which getting progressively smaller behind it. Premaxillary teeth are unknown, but it possibly had another pair of larger 'pseudocanines' in the upper jaw. It is estimated that there were only 13 teeth in each lower jaw, and at least 13—14 in the upper jaw, a relatively small number compared to other sebecosuchians like Iberosuchus. The teeth are not as strongly compressed as other ziphodont crocodilians, and so may have been stronger and more resistant to stress. Rossmann and colleagues estimated the total body length of Bergisuchus to be around 1.5 metres (4.9 ft) based on other short-snouted, partially terrestrial crocodylians including Allognathosuchus and the extant dwarf caimans Paleosuchus. Despite its small size, they believed both specimens to represent mature adults, based on both the degree of fusion between the sutures in the skull and the extent of the dermal sculpting on the surface of the bones. As a sebecosuchian, Bergisuchus likely had long limbs that were positioned directly under its body and moved with a parasagittal gait, unlike the sprawling limbs of modern crocodylians. It is unknown if it had a reduced covering of osteoderms like some other sebecosuchians, but no osteoderms were found associated with either individual (although isolated osteoderms have been tentatively referred to this genus). Bergisuchus was identified as a sebecosuchian by Dr. Berg when it was first discovered, closely allied to the South American genus Sebecus as 'aff. Sebecus? n. sp.'. It was later variously assigned to the family Baurusuchidae by Steel in 1973, and also in the now defunct family Trematochampsidae by Buffetaut in 1988. At the time it was unclear what diagnostic traits where unique to each group and which were shared between them, and so the fragmentary Bergisuchus could not be confidently identified and was sometimes placed in incertae sedis for this reason. In 2000, the sebecosuchian affinities of Bergisuchus, particularly to Sebecus, were established by Rossmann and colleagues in a thorough re-examination of the material, and it was assigned to its own monotypic family, the Bergisuchidae, as it was considered too distinct from Sebecus to belong to the same family.