Madtsoiidae are a group of archaic snakes, widely distributed in the Upper Cretaceous of Gondwanan landmasses (South America, Madagascar, India, Africa), but otherwise reported outside Gondwana based only on scarce material from a few southern European localities. Here, we describe associated snake remains from uppermost Cretaceous (Maastrichtian) beds of the Hajeg Basin, Romania, as a new small-madtsoiid taxon, Nidophis insularis, gen. et sp. nov. Nidophis, represented by a large number of well-preserved vertebrae and ribs that apparently belonged to one individual, is one of the best-known Cretaceous madtsoiids, and the most completely documented member of the family from Europe. Phylogenetic analyses place the new taxon within a moderately supported Madtsoiidae, closely related to Herensugea from the Upper Cretaceous of Spain. The two European taxa, together with other small madtsoiids, are recovered as the sister taxon to a second madtsoiid clade including large-to-gigantic forms such as Madtsoia, Wonambi, and Yurlunggur. The presence of these small madtsoiids, together with that of Menarana, in the uppermost Cretaceous of Europe, suggests that early widespread distribution of madtsoiids, extending over the southern part of Europe, instead of late northward immigration from Gondwanan landmasses, as proposed previously, might account for the paleobiogeographic distribution of Cretaceous Madstoiidae.

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