A new small short-snouted dyrosaurid (Crocodylomorpha, Mesoeucrocodylia) from the Paleocene of northeastern Colombia

Abstract

Prior to this study, specimens from South America have been limited to a few fossils with only two taxa diagnosed. We describe a nearly complete skull and unassociated mandible of a new dyrosaurid, Cerrejonisuchus improcerus gen. et sp. nov., from the Paleocene Cerrejón Formation of northeastern Colombia. The skull of C. improcerus has relatively elongate supratemporal fenestrae and well-developed occipital tuberosities, both diagnostic characteristics of Dyrosauridae. The rostrum of adult C. improcerus comprises 54-59% of the length of the skull, making it the shortest snout of any known dyrosaurid. A cladistic analysis using 82 cranial and mandibular characters for all species of Dyrosauridae known from crania yielded two most-parsimonious cladograms with C. improcerus as the sister taxon to a clade including Arambourgisuchus, Dyrosaurus, Hyposaurus, Congosaurus, Rhabdognathus, Atlantosuchus, and Guarinisuchus. Only Chenanisuchus, Sokotosuchus, and Phosphatosaurus, all known only from Africa, are more primitive within Dyrosauridae. Chenanisuchus from the Paleocene of Morocco, the only other known short-snouted dyrosaurid, is not closely related to C. improcerus and a short-snouted condition appears to have evolved independently at least twice within Dyrosauridae. Our analysis supports an African origin of Dyrosauridae with dispersals to the New World by the Late Cretaceous or earliest Paleocene. The presence of C. improcerus, together with undescribed taxa from the Cerrejón Formation, suggests a radiation of dyrosaurid crocodyliforms, possibly following the K-P boundary, in tropical South America.

New dyrosaurid remains (Crocodyliformes, Mesoeucrocodylia) from the Paleocene of the Paraíba Basin, NE Brazil

“…The alveolar edges of d4 are higher than the edges of the other alveoli. The d7 alveoli are reduced and close to the eighth alveoli border as described for D. maghribensis (OCP DEK-GE 253) (Jouve et al, 2006) and C. improcerus (UF/IGM 29) (Hastings et al, 2010); this pattern was also found in an unidentified dyrosaurid, VPL/JU/IR/400, from Maastrichtian strata in India (Khosla et al, 2009). The tenth alveolus is not preserved on the right side of the dentary.…”

“…The siphonial foramen is lacking in the medial view in this specimen, as in Guarinisuchus munizi. In contrast to this feature, Rhabdognathus aslerensis Jouve, 2008 (CNRST-SUNY-190) (Brochu et al, 2002) and Cerrejonisuchus improcerus (UF/IGM 29) (Hastings et al, 2010) share the condition of presence of the siphonial foramen in medial view. Mandible.…”

“…Interalveolar occlusal pits are distributed among the alveoli on the lateral margin of both sides of the mandible, and they are smaller and shallower than the alveoli. The largest diastema is located between d2 and d3, probably to fit enlarged 3 rd premaxillary teeth (Jouve et al, 2006;Hastings et al, 2010). There are three neurovascular foramina near the medial margin of the third alveoli, two on the left side and one on the right side.…”

“…These crocodyliforms are found from marine, nearshore (Troxell, 1925;Brochu et al, 2002;Jouve & Schwartz, 2004;Hill et al, 2015), and freshwater environmental deposits (Buffetaut, 1978;Khosla et al, 2009;Hastings et al, 2010Hastings et al, , 2011Hastings et al, , 2015.…”

Sea surface temperature contributes to marine crocodylomorph evolution

“…An additional approach was applied to this generic data set for further refinement of the diversity: phylogenetic correction, superimposed on the stratigraphy by filling ghost ranges of genera (Supplementary Data 1). Phylogenetic corrections follow the topology recovered for Thalattosuchia 31 and the topology recovered for Dyrosauridae 34 . Pholidosauridae (two marine genera) are, in comparison with Thalattosuchia and Dyrosauridae, a relatively small marine radiation with a larger ancestral freshwater stock.…”