New finds of the turtle Plesiochelys in the Upper Jurassic of Portugal and evaluation of its diversity in the Iberian Peninsula

Abstract

ABSTRACT Two unpublished shells of thalassochelydian turtles from Tithonian (Late Jurassic) outcrops of the Lusitanian Basin (west central Portugal) are studied here. They are recognised as attributable to the plesiochelyid littoral genus Plesiochelys. They show characters unknown for the so far available Portuguese record of Plesiochelys, exclusively based on a partial shell, also from the Tithonian. The comparison between all these specimens and the only remains of Plesiochelys from the Spanish Tithonian record allow us to recognise several differences, compatible with the intraspecific variability reported for the genus. One of the oldest references to Thalassochelydia for the global record corresponds to that of the enigmatic taxon ‘Hispaniachelys prebetica’, from the Oxfordian of Jaén (Spain), hitherto recognised as a nomen dubium. Its holotype is identified here as belonging to the oldest member of Plesiochelys, the new combination Plesiochelys prebetica being proposed. Thus, the presence of at least two forms of Plesiochelys is recognised for the Iberian record, one of them corresponding to the only one identified at levels older than the middle Kimmeridgian, and the other being younger than the two species of which the shell was known (i.e. Plesiochelys etalloni and Plesiochelys bigleri).