Halisaurus sp (Mosasauridae) from the upper Cretaceous (?Santonian) of east-central Peru, and the taxonomic utility of mosasaur cervical vertebrae

A cervical vertebra, collected from Upper Cretaceous (?Santonian) sediments in east-central Peru, is described and assigned to the genus Halisaurus. The Peruvian specimen shows the centrum and condyle-cotyle morphology considered to characterize halisaurines. The centrum is elongate and extremely compressed dorsoventrally, as are the cotyle and condyle. The condylar facet also has a dorsally expanded articular surface. The hypapophysis is very large and flared distally. A morphometric comparison of centrum shape characters in mosasaur cervical vertebrae shows characteristic generic and family-level variations in the cervical column. In halisaurines, cervical series variation is unique between cervicals three to five. We find that qualitative identification of isolated halisaurine cervicals is supported by quantitative analyses which evaluate the degree of dorsal-ventral compression. The known diversity of halisaurines is limited and many age and locality records are based on cervical vertebrae. This record significantly expands the geographic and temporal range of halisaurine mosasaurs and is a first report for South America. The stratigraphically earliest halisaurine is North American (Coniacian-Santonian), followed by lower Campanian to upper Maastrichtian specimens from North America, and specimens from the upper Maastrichtian of central Africa and western Europe.