Abstract A new incomplete skull of Nothosaurus marchicus was found in the Lower Muschelkalk of Winterswijk below the layers in which Nothosaurus winterswijkensis specimens are normally found. Although this skull resembles N. marchicus more closely than it does N. winterswijkensis it has several features which suggest an intermediate position. The specimen shares with N. marchicus, apart from general size, five teeth preceeding the maxillary fangs, the body of the vomer not extending backwards for a greater distance than the longitudinal diameter of the internal naris and the absence of an anteromedial process of the prefrontal. It shares with N. winterswijkensis however that the prefrontal excludes contact between the maxilla and the frontal, the fifth premaxillary fang being distinctly smaller and the jugal entering (or at least almost entering) the orbit. As all other specimens of N. marchicus originate from localities further to the east and the presumed transgression of the Anisian Muschelkalk is from east to west, it is assumed that N. marchicus is an older species than N. winterswijkensis. Phylogenetic interrelationships however have put N. winterswijkensis at a more basal position than N. marchicus, which has now definitively been proven wrong by the stratigraphy of the Winterswijk finds.


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