A new European Late Jurassic pleurosternid (Testudines, Paracryptodira) and a new hypothesis of paracryptodiran phylogeny

摘要

Paracryptodira was an abundant and diverse group of freshwater turtles, recognized both in North America and Europe. Its known record spans the Middle Jurassic to the Eocene. The internal phylogenetic relationships of one of its clades, Baenidae, are relatively well known. However, information on the relationships amongst the non-baenid members is very limited and, so far, poorly justified. A new study on the phylogenetic relationships amongst Paracryptodira is undertaken here through the revision of previously described taxa, the incorporation of information on taxa recently discovered or revised, and the study of new material. In addition, a new taxon from the Late Jurassic of Europe is described: Riodevemys inumbragigas gen. et sp. nov. It is identified as a member of Pleurosternidae, constituting the first generic and specific attribution of a pleurosternid in the Spanish fossil record. Pleurosternidae is obtained here as a robust node whose composition differs from previous proposals. The relationships amongst representatives are analysed. In addition, we define a new clade, Compsemydidae, identified as the sister group of Baenoidea (Baenidae + Pleurosternidae). The new phylogenetic proposal, and its analysis in view of stratigraphical distributions, shows that Baenidae was a clade of turtles only known in the Cretaceous and Palaeogene of the North American record but that Pleurosternidae and Compsemydidae were distributed both in North America and Europe. The temporal distribution of Pleurosternidae is restricted here, refuting some putatively older and younger occurrences. This new hypothesis restricts its known distribution to the Late Jurassic of North America and the Late Jurassic and the first part of the Early Cretaceous of Europe. The new clade Compsemydidae is recognized in the Late Cretaceous and Palaeocene of North America and in younger levels of the European Palaeocene.