New contributions to the skull anatomy of spinosaurid theropods: Baryonychinae maxilla from the Early Cretaceous of Igea (La Rioja, Spain)

Spinosaurid dinosaurs show a wide geographical and temporal distribution, being present in Gondwanan and Laurasian landmasses, at least, during the Lower Cretaceous and the Cenomanian. European spinosaurids are more diverse than previously thought with five, and probably six, currently recognised genera. The revision of CPI 477, a fragment of a left maxilla from the Lower Cretaceous of La Rioja (Spain) previously assigned to Baryonyx, demonstrates that this specimen cannot be referred to this genus and likely belongs to an indeterminate baryonychine closer to Baryonyx than to Suchomimus. CPI 477 exhibits a tooth replacement process comparable to that of other theropods and, besides, similar to other large theropods, two replacement teeth could simultaneously be developed in the same alveolus, partly explaining high replacement ratios and the overabundance of spinosaurid teeth in some fossil sites. Furthermore, the Oxalaia maxilla shares the anteriorly located external naris with Irritator and baryonychine spinosaurids, which differ from the more retracted ones in African spinosaurines. Finally, in addition to the previously noticed differences between Baryonychinae and Spinosaurinae, the paradental groove of African spinosaurines and Oxalaia differs from that of baryonychines in being sinusoidal instead of straight.