A new species of Dyrosaurus (Crocodylomorpha, Dyrosauridae) from the early Eocene of Morocco: phylogenetic implications

Abstract

A new dyrosaurid is described from the Ypresian of the phosphatic deposits of the Oulad Abdoun Basin of Morocco. It is based on numerous cranial and postcranial remains, allowing an almost complete reconstruction. This new Dyrosaurus species, Dyrosaurus maghribensis sp. nov. , is currently only known from Morocco. It differs from D. phosphaticus , present in contemporaneous levels of Algeria and Tunisia, by several autapomorpies, including a smooth dorsal margin of the parietal and widely opened choanae. A phylogenetic analysis, using 47 taxa and 234 morphological characters, shows the dyrosaurids as the sister taxon of pholidosaurids, which include Elosuchus , Sarcosuchus , Terminonaris and Pholidosaurus , and the thalattosuchians. Goniopholididae is a non-monophyletic group; however, if dyrosaurids are not included in the analysis, the result differs and the goniopholidids form a distinct clade. If Thalattosuchia is excluded, both Goniopholididae and Pholidosauridae become paraphyletic assemblages. Thus, phylogenetic problems remain with respect to longirostrine clade, and more attention should be paid to resolving their evolutionary relationships amongst the crocodyliforms.

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 first tooth is oriented anterodorsally and the largest teeth are located at positions d1 and d4. Likewise, the d4 tooth is the largest in Dyrosaurus phosphaticus Thomas, 1893 (MNHN ALG 3 and MNHN APH 27) (Jouve, 2005) and in Dyrosaurus maghribensis Jouve, Iarochène, Bouya & Amaghzaz, 2006 (OCP DEK-GE 253), (Jouve et al, 2006). The alveolar edges of d4 are higher than the edges of the other alveoli.…”

“…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.…”

“…The splenial forms the medial edges of the alveoli from the d10 position to the posterior-most alveolus. In D. maghribensis, OCP DEK-GE 253, these bones reach anteriorly to the position of the d11 to d14 teeth (Jouve et al, 2006). Reduction of tooth size, from the anterior to the posterior portion of the mandible, has been described for some dyrosaurids species (Jouve & Schwartz, 2004;Jouve, 2005;Hastings et al, 2011).…”

“…In Arambourgisuchus khouribgaensis Jouve et al, 2005, OCP DEK-GE 18, the symphysis ends posteriorly at the position of the d16 tooth. In D. maghribensis, OCP DEK-GE 253, the symphysis reaches, posteriorly, the position of the d17-d21 alveoli (Jouve et al, 2006). In C. improcerus, UF/IGM 30, the mandibular symphysis ends posteriorly at approximately the level of the d9 alveolus, due to its short snout (Hastings et al, 2010).…”