Skeletal material from larger Eusauropterygia (Reptilia: Eosauropterygia) with nothosaurian and cymatosaurian affinities from the Lower Muschelkalk of Winterswijk, The Netherlands

Eusauropterygian elements from the Lower Muschelkalk (Vossenveld Formation) of Winterswijk, The Netherlands, comprising three mandibles and a selection of postcranial material, are described. The new mandibles correspond to crania larger than eusauropterygian cranial material previously known from this locality. The postcranial material represents a selection of isolated and associated material of comparably large size. Two of the mandibles conform to the morphology commonly recognized in Nothosaurus from the Lower Muschelkalk, but the third mandible accommodates five fangs per ramus in the symphyseal domain and exhibits a symphyseal ratio of 1.04, a condition not yet described for Eusauropterygia from the Vossenveld Formation. Body length for the animals represented by the finds was estimated through dimensional comparison with MB.R.27, a nearly complete skeleton from the lower Middle Muschelkalk locality of Rüdersdorf (Germany) assigned to Nothosaurus marchicus . Body length estimates for the individuals represented by the largest mandible and by a selection of associated postcranial material exceed 1,500 mm; approximately 50 % larger than the eusauropterygian taxa from Winterswijk described so far. Furthermore, certain morphological characters identified in one mandible and in the postcranial elements suggest a cymatosaurian affinity over a nothosaurian affinity. The present study indicates eusauropterygian diversity during the Lower Muschelkalk was greater than traditionally believed. This challenges the concept of a slow paced, gradual biotic response to the origination and expansion of the Muschelkalk Sea, which commenced only 5 million years after the Permian–Triassic mass extinction event.