Abstract

A new genus and two new species of mosasaurs are described from five specimens collected during quarrying operations in the ‘Lastame’ lithotype located in the mountains of northern Italy just to the north of Verona (lower Turonian–lower Santonian). These mosasaurs share some anatomical characters with the North American taxon Russellosaurus coheni, but the presence of distinctive features suggests placement into two new species within a new genus (e.g., forked distal tip of suprastapedial process of quadrate; suture between maxilla and premaxilla extends to point above third tooth position [cf. second in Russellosaurus]). We conducted two phylogenetic analyses of the Mosasauroidea (37 ingroup taxa, 131 characters), the first one with equally weighted characters and the second after successive weighting in order to reduce homoplastic noise and amplify the signal in the data. The first analysis (equal weights) resulted in 96 most parsimonious trees, whereas the second produced a single shortest tree. Both analyses consistently placed the new genus as the sister taxon to Russellosaurus, and these two taxa were placed together with Yaguarasaurus, in a clade that is the sister group of the Tethysaurinae (Tethysaurus and Pannoniasaurus). A new clade of mosasaurs, the Yaguarasaurinae, is here defined as comprising the most recent common ancestor of Russellosaurus, Romeosaurus, and Yaguarasaurus, and all of its descendants.