Abstract
Fossil sites from Brazil have yielded specimens of spinosaurid theropods, among which the most informative include the cranial remains of Irritator, Angaturama, and Oxalaia. In this work some of their craniodental features are reinterpreted, providing new data for taxonomic and evolutionary issues concerning this particular clade of dinosaurs. The mesial-most tooth of the left maxilla of the holotype of Irritator is regarded as representing the third tooth position, which is also preserved in the holotype of Angaturama. Thus, both specimens cannot belong to the same individual, contrary to previous assumptions, although they could have been the same taxon. In addition, the position of the external nares of Irritator is more comparable to those of Baryonyx and Suchomimus instead of other spinosaurine spinosaurids. In fact, with regards to some craniodental features, Brazilian taxa represent intermediate conditions between Baryonychinae and Spinosaurinae. Such a scenario is corroborated by our cladistic results, which also leave open the possibility of the former subfamily being non-monophyletic. Furthermore, the differences between spinosaurids regarding the position and size of the external nares might be related to distinct feeding habits and degrees of reliance on olfaction. Other issues concerning the evolution and taxonomy of Spinosauridae require descriptions of additional material for their clarification.
Highlights
Spinosauridae are among the most iconic dinosaur groups of all time [1]
Spinosaurid that differs from Baryonyx, Suchomimus, and Cristatusaurus by the unserrated condition of its teeth and nearly half the number of maxillary alveoli
Spinosaurid that differs from Baryonyx, Suchomimus, and Cristatusaurus by both the possession of unserrated teeth and the comparatively smaller first premaxillary tooth
Summary
Spinosauridae are among the most iconic dinosaur groups of all time [1]. This status is strengthened every time a new study on them is published (e.g., [2,3,4,5,6,7]). The history of the knowledge on spinosaurids began in 1912, when the fossil collector Richard Markgraf unearthed a partial skeleton with neural spines up to 165 cm in height from the Bahariya Oasis, western Egypt [8,9]. These remains, which represented the holotype of Spinosaurus aegyptiacus Stromer, 1915 and were housed at the Palaontologische Staatssammlung Munchen, were destroyed by a British air raid on Munich during World War II, along with other specimens referred to that genus [1,8,9,10,11].
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