The maxillary depression of Pholidosauridae: an anatomical study

Abstract

Goniopholidids and pholidosaurids are common crocodilians in Late Jurassic and Early Cretaceous freshwater environments in many parts of the world, although evidence that goniopholidids ever reached Gondwanan regions needs to be substantiated. In the ‘mid’-Cretaceous, some pholidosaurids (Terminonaris, Oceanosuchus) became adapted to life in the sea, a domain that goniopholidids apparently never occupied. Whereas goniopholidids were mainly mesorostral forms, pholidosaurids were longirostral. There is currently no consensus about the phylogenetic relationships between goniopholidids and pholidosaurids. They have been considered as closely related on the basis of various shared characters (Buffetaut, 1982), but in some recent phylogenetic analyses (e.g., Jouve et al., 2006; Jouve, 2009; Pol et al., 2009) at least some pholidosaurids cluster with other longirostral forms such as dyrosaurids and thalattosuchians, which may suggest that the family Pholidosauridae is not monophyletic. Nevertheless, a number of characters uniting Pholidosauridae have recently been proposed (Hua et al., 2007), but were not tested in a phylogenetic framework. On the other hand, only one unambiguous character diagnoses the clade Goniopholididae in phylogenetic studies: the presence of a depression on the posterior end of the maxilla, described as the ‘depression maxillaire’ (maxillary depression) by Buffetaut (1982; see also Lauprasert et al., 2007). On this basis, Goniopholididae is accepted as a monophyletic entity comprising the generaCalsoyasuchus,Goniopholis,Eutretauranosuchus, Siamosuchus, and Sunosuchus (Tykoski et al., 2002; Lauprasert et al., 2007; Smith et al., 2010), thus agreeing with pre-cladistic views (Buffetaut, 1982). Functionally, the maxillary depression may have housed a sensory organ helping to localize and capture prey in the aquatic environment (Brandalise de Andrade, 2009). Here, we report for the first time the presence of a maxillary depression in Pholidosauridae. Its morphology and position is for the first time described in taxa where the maxillojugal area is preserved. Implications for a close relationship between Goniopholididae and Pholidosauridae are discussed on the basis of this previously overlooked character. Institutional Abbreviations—AMNH, American Museum of Natural History, New York, U.S.A.; BYU, Brigham Young University, Provo, Utah, U.S.A.; CHE, Universite Lyon 1, Lyon, France, specimen from Cherves de Cognac; CMNH, Cleveland Museum of Natural History, Cleveland, Ohio, U.S.A.; DORCM, Dorset County Museum, Dorchester, United Kingdom; MNHN, Museum National d’Histoire Naturelle, Paris, France;MNN, Musee National du Niger, Niamey, Republique du Niger; NHMUK, The Natural History Museum, London, United Kingdom.