New interpretations of Dortoka vasconica Lapparent de Broin and Murelaga, a freshwater turtle with an unusual carapace

The discovery of abundant new material of the European turtle Dortoka vasconica at its type locality and a review of the previously analyzed material allow new interpretations of the anatomy and lifestyle of this Cretaceous taxon to be proposed. Both its carapace and plastron are highly varied and several characters are identified as subject to individual variability. Some characters previously considered in the diagnosis of this taxon were found to vary. Two morphotypes of the anterior lobe of the plastron are identified, both of which are characterized by a particular morphology and disposition of their bony elements and scute patterns. We also identified two morphotypes taking into account the morphology of the anal notch, which are potentially related to two sexual morphs. The curious shape of various elements of the carapace had been mentioned previously. We identify here the presence of a pair of autapomorphic fontanelles, which justify the development of these peculiar structures. The presence of these large fontanelles, which remain open throughout ontogeny, and a histological study examining various elements of the carapace and plastron corroborate our interpretation of Dortoka vasconica as having a more aquatic lifestyle than previously thought.