A new description of the skull of Dyrosaurus phosphaticus (Thomas, 1893) (Mesoeucrocodylia: Dyrosauridae) from the Lower Eocene of North Africa

Dyrosaurus phosphaticus (Thomas 1893) has been described several times, but the poor preservation and the incomplete preparation of the material left this species inadequately described. Further preparation of a specimen referred to this species now allows a complete description of the braincase and its various cranial nerves. Dyrosaurid taxonomy is mainly based on mandibular characters and the complete description of the skull of D. phosphaticus, and comparison with the other known species of the family enables enhancement of other taxonomic characters. An emended diagnosis is given for D. phosphaticus, the only known species of this genus. With this new description, new characteristics that enable comparisons with other crocodyliforms are available. The presence of a distinct anterolateral postorbital process is observed in dyrosaurs, Elosuchus, Terminonaris robusta, some Goniopholis, and, although smaller, in Sarcosuchus imperator. In the dyrosaurids D. phosphaticus and Rhabdognathus, the postorbital participates largely in the dorsal margin of the infratemporal fenestra, as in Elosuchus, S. imperator, and Thalattosuchia. The laterodorsal position of the lateral eustachian foramen in dyrosaurids is similar to those of Elosuchus and thalattosuchians. These characters are not shared by Stolokrosuchus lapparenti (included in the family Elosuchidae with Elosuchus), suggesting that without clear phylogenetic analysis, the creation of the Elosuchidae was premature. A preliminary phylogenetic analysis based on comparisons of D. phosphaticus with other dyrosaurids shows that Phosphatosaurus gavialoides and Sokotosuchus ianwilsoni are the most primitive dyrosaurids, and Rhabdognathus is more closely related to Hyposaurus than to D. phosphaticus.