New information on the anatomy and paleobiogeographic and stratigraphic distributions of the British basal turtle Plastremys lata (Helochelydridae) based on its most complete skeleton (lower Albian, Spain)

The synchronous and sympatric presence of two helochelydrids is reported here for the first time for the Spanish Municipality of Ariño (Teruel Province), where the most complete skeletons from that group had been found for the European record. The presence of two members of this lineage of basal turtles has been documented in very few localities worldwide, and until now consisted of isolated and fragmented remains. Although the lower Albian Aragochersis lignitesta is exclusively documented in this Spanish paleontological area, the new material from Ariño is identified as the oldest occurrence for the British Plastremys lata, extending the paleobiogeographic distribution range for that taxon. The new fossils include a partial skeleton, as well as isolated remains of several individuals. Their analysis not only shows intraspecific variability, but also documents several anatomical elements previously unknown for Plastremys lata, which was only known from shell remains. Furthermore, the status of the first Mesozoic turtle taxon defined for the Spanish record (i.e., the hitherto problematic ‘Trachyaspis turbulensis’, also from the lower Albian of Teruel) is examined and its holotype, whose original anatomical attribution is here revised, is reattributed to Plastremys lata.