| Cerrejonisuchus | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Archosauria |
| Clade: | Pseudosuchia |
| Clade: | Crocodylomorpha |
| Clade: | Crocodyliformes |
| Family: | †Dyrosauridae |
| Genus: | †Cerrejonisuchus Hastingset al.,2010 |
| Type species | |
| †Cerrejonisuchus improcerus Hastingset al., 2010 | |
Cerrejonisuchus is an extinctgenus ofdyrosauridcrocodylomorph. It is known from a complete skull and mandible from theCerrejón Formation in northeasternColombia, which isPaleocene in age. Specimens belonging toCerrejonisuchus and to several other dyrosaurids have been found from theCerrejónopen-pit coal mine inLa Guajira. The length of the rostrum is only 54-59% of the total length of the skull, making the snout ofCerrejonisuchus the shortest of all dyrosaurids.[1]
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 specimensUF/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 ofCerrejonisuchus are UF/IGM 29 (thetype 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 dorsalvertebrae are closed, an indication of morphological maturity. Additionally, the presence of well-developedosteoderms 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 lateontogenic stage. In contrast, UF/IGM 32 has an unfusednasal 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 ofCerrejonisuchus is the shortest of any dyrosaurid. It, along withChenanisuchus, are the only short-snouted dyrosaurids. The snout ofCerrejonisuchus is narrow and consistent in width from the external nares, ornostril openings, to theorbits, 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 ofCerrejonisuchus is generallyhomodont, although the thirdmaxillary 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. Thepremaxillary teeth are generally thinner and longer than the maxillary teeth. LikeChenanisuchus,Cerrejonisuchus visibly lacks striations on the tooth surfaces. Unlike many other dyrosaurids, includingDyrosaurus maghribensis,Atlantosuchus coupatezi,Guarinisuchus munizi,Phosphatosaurus gavialoides, andSokotosuchus ianwilsoni, the teeth ofCerrejonisuchus are not curved.[1]
Aphylogenetic analysis of dyrosaurids by Hastingset al. (2010) placedCerrejonisuchus relativelybasally in the dyrosaur clade betweenPhosphatosaurus gavialoides andArambourgisuchus khouribgaensis.Cerrejonisuchus was not found to be closely related to the other short-snouted dyrosaurChenanisuchus, which was placed at the base of the clade. Although it might be expected thatChenanisuchus andCerrejonisuchus 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 thecladogram from Hastingset al. (2010) showing the phylogenetic relationship ofCerrejonisuchus within Dyrosauridae:[1]
Cerrejonisuchus likely had a diet consisting of fish, invertebrates, frogs, lizards, small snakes, and possibly mammals.[1][2] The short snout ofCerrejonisuchus is thought to be an adaptation to such a generalized diet. Other long-snouted marine dyrosaurs are presumed to have had a strongly piscivorous diet consisting solely of fish. With its short snout,Cerrejonisuchus would have been able to occupy a newecological niche in the neotropical rainforest environment of Paleocene Colombia.[2]
The presence of homodont dentition with compressed teeth similar to those ofsebecians and other terrestrial crocodylomorphs has been used as an argument for a terrestrial predatory lifestyle, though unlike other terrestrial crocodylomorphs it has a flat skull.[3]
Compared to other dyrosaurids,Cerrejonisuchus has stronger limbs and a cylindrical torso, suggesting a primarily terrestrial ecology as opposed to the semi-aquatic habits of modern crocodilians and the fully marine habits of other dyrosaurids.[4]
Cerrejonisuchus is known from the Middle to Late Paleocene Cerrejón Formation. All known specimens have been found from the Cerrejón open-pit coal mine at the La Puente Pit below Coal Seam 90. The mine has also yielded remains ofTitanoboa cerrejonensis, a recently described 12.8 metres (42 ft) long extinctboid that is the largest known snake to have ever existed.[5] LikeCerrejonisuchus, fossils ofTitanoboa were found in a grayclaystone layer directly underlying Coal Seam 90.[6] Additional dyrosaurid material has been found from the Cerrejón Formation alongside that ofCerrejonisuchus, and is thought to represent at least two different taxa. The age of the Cerrejón Formation has been dated as Middle-Late Paleocene based oncarbonisotopes,pollen,spores, anddinoflagellate cysts.[7]
The section of the Cerrejón Formation from which fossils ofCerrejonisuchus have been found was likely deposited in a transitional environment, probablybrackish water in ariver-to-lagoonal setting. Large freshwaterpodocnemididturtles anddipnoan andelopomorphfishes have also been found from this part of the formation.[8]Cerrejonisuchus may have been a food source forTitanoboa, which would have lived in the same brackish water environment.[2] The vertebrate paleofauna of the Cerrejón Formation was similar to modern neotropical riverine vertebrate faunas.[5]
During the Paleocene, river systems would have incised acoastal plain covered by a wetneotropicalrainforest. The global temperature was much warmer than it is today, based on paleoclimate models. The latitudinal temperature gradient between the equator and mid-latitudes of South America was similar to the gradient that exists today. Elevated levels ofcarbon dioxide in the atmosphere are thought to have caused the global greenhouse temperature. The high rainfall estimates and increased pCO2 would have maintained the rainforest floras during the Paleocene greenhouse.[5]
The presence of dyrosaurids such asCerrejonisuchus in the Paleocene of Colombia suggests that there was a radiation of dyrosaurids in South America following theCretaceous–Paleogene boundary (K–T boundary) and theCretaceous–Paleogene extinction event. There may have been a dispersal fromAfrica toBrazil, and continued immigration intoNorth America.[9] Colombia can be seen as a transitional route from Brazil to North America, and also toBolivia, assuming that it was coastal.[1]
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