A re-examination of the anatomy and systematics of the tomistomine crocodylians from the Miocene of Italy and Malta

摘要

Once a much more globally widespread crocodylian clade, Tomistominae is today represented by just one species, Tomistoma schlegelii (the false gharial), restricted to south-east Asia. Although tomistomine fossil occurrences are recognized from the early Eocene (similar to 55 Ma) onwards, their remains are often incomplete, making appropriate taxonomic classification within the group problematic. This is especially pertinent to several taxa from the Miocene of Europe, which were historically erected from fragmentary remains. Here we re-examine and describe four approximately contemporaneous taxa from Malta and Italy to determine their taxonomy and phylogenetic affinities: Melitosaurus champsoides, Tomistoma calaritanum, Tomistoma gaudense and Tomistoma lyceense. We place them into a phylogenetic analysis for the first time, comprising 70 taxa scored for 244 characters, several of which are revised or novel, and apply a number of character weighting strategies. Whereas 'Tomistoma lyceense' is deemed to be an indeterminate tomistomine, a unique combination of features confirms Melitosaurus champsoides, Tomistoma calaritanum and Tomistoma gaudense as three distinct species. These three taxa are recovered as derived tomistomines, with characters such as a posterior maxillary process between the lacrimal and nasal, large supratemporal fenestrae that are wider than long, and the posteromedial alignment of the last three premaxillary teeth, suggesting a close relationship with the approximately contemporaneous European taxa, Tomistoma lusitanica and Gavialosuchus eggenburgensis. It is unlikely that any of these species belong to Tomistoma, with the possibility that they can all be classified under Melitosaurus and Gavialosuchus. However, we retain them in open nomenclature pending reassessment of the remaining European Miocene tomistomines. Our taxonomic and phylogenetic revision helps to elucidate past tomistomine diversity in the Miocene of the Mediterranean region, prior to the group's extirpation, and is an important first step in resolving the complicated history of European tomistomine systematics.