Cerrejonisuchus

Cerrejonisuchus is an extinct genus of dyrosaurid crocodylomorph. It is known from a complete skull and mandible from the Cerrejón Formation in northeastern Colombia, which is Paleocene in age. Specimens belonging to Cerrejonisuchus and to several other dyrosaurids have been found from the Cerrejón open-pit coal mine in La Guajira. The length of the rostrum is only 54-59% of the total length of the skull, making the snout of Cerrejonisuchus the shortest of all dyrosaurids.

Description
At an estimated length of 1.22 metres (4.0 ft) to 2.22 metres (7.3 ft), Cerrejonisuchus was small for a dyrosaur. This size estimate is based on the dorsal skull lengths of specimens UF/IGM 29 and UF/IGM 31. Cerrejonisuchus has the shortest body length of any known dyrosaur, much smaller than that of the longest dyrosaur, Phosphatosaurus gavialoides, which was 7.22 metres (23.7 ft) to 8.05 metres (26.4 ft) in length.[1]

Currently the only known specimens of Cerrejonisuchus are UF/IGM 29 (the type specimen), UF/IGM 30, UF/IGM 31, and UF/IGM 32. Of these, UF/IGM 29 and UF/IGM 31 are thought to represent fully mature individuals while UF/IGM 32 is thought to represent a less mature individual. In UF/IGM 31, the neurocentral sutures of the anterior dorsal vertebrae are closed, an indication of morphological maturity. Additionally, the presence of well-developed osteoderms is likely to be an indication that the animal was mature because in living crocodylians, the osteoderms begin calcification after 1 year and grow to articulate with other osteoderms to form a dermal shield at maturity. Also, the sutures that separate the bones of the skull in both specimens are fully fused, suggesting that the individuals have reached a late ontogenic stage. In contrast, UF/IGM 32 has an unfused nasal suture, suggesting that it was less mature than the other individuals. UF/IGM 32 is also noticeably smaller than the other specimens.[1]

Relative to the entire skull length, the rostrum of Cerrejonisuchus is the shortest of any dyrosaurid. It, along with Chenanisuchus, are the only short-snouted dyrosaurids. The snout of Cerrejonisuchus is narrow and consistent in width from the external nares, or nostril openings, to the orbits, or eye sockets. The margin of the snout, unlike that of many long-snouted dyrosaurids, is smooth rather than festooned. "Festooned" refers to the lateral undulations in the maxillae and premaxillae that form around the tooth sockets, or alveoli. The external nares are positioned extremely anteriorly at the very tip of the snout. The orbits are oriented anterodorsally, facing upward and slightly forward. The dentition of Cerrejonisuchus is generally homodont, although the third maxillary tooth is enlarged and the fourth is somewhat smaller than the rest. They are conical, labiolingually compressed, each having a relatively rounded apex. The carinae, or tooth edges, are strongly developed both anteriorly and posteriorly. The premaxillary teeth are generally thinner and longer than the maxillary teeth. Like Chenanisuchus, Cerrejonisuchus visibly lacks striations on the tooth surfaces. Unlike many other dyrosaurids, including Dyrosaurus maghribensis, Atlantosuchus coupatezi, Guarinisuchus munizi, Phosphatosaurus gavialoides, and Sokotosuchus ianwilsoni, the teeth of Cerrejonisuchus are not curved.

Classification
A phylogenetic analysis of dyrosaurids by Hastings et al. (2010) placed Cerrejonisuchus relatively basally in the dyrosaur clade between Phosphatosaurus gavialoides and Arambourgisuchus khouribgaensis. Cerrejonisuchus was not found to be closely related to the other short-snouted dyrosaur Chenanisuchus, which was placed at the base of the clade. Although it might be expected that Chenanisuchus and Cerrejonisuchus are closely related because they are the only dyrosaurids with short snouts, the results of the analysis show that snout proportions alone are not indicative of phylogenetic relatedness in dyrosaurs.

Below is the cladogram from Hastings et al. (2010) showing the phylogenetic relationship of Cerrejonisuchus within Dyrosauridae: