Two new plioplatecarpine (Squamata, Mosasauridae) genera from the Upper Cretaceous of North America, and a global phylogenetic analysis of plioplatecarpines

ABSTRACT

A new plioplatecarpine taxon, Latoplatecarpus, gen. nov., is proposed here to incorporate two species, L. willistoni, sp. nov., and L. nichollsae (comb. nov.). The new genus is currently restricted in distribution to the lower middle Campanian of North America. Phylogenetic analysis incorporating 97 morphological characters and 17 ingroup taxa indicates that (1) Ectenosaurus clidastoides is the basal-most member within the Plioplatecarpinae; (2) Platecarpus planifrons is generically distinct from P. tympaniticus; (3) Latoplatecarpus willistoni, gen. et sp. nov., constitutes the basal-most member within the clade that is sister to Platecarpus tympaniticus; and (4) as many as 17 unequivocal character changes support the clade comprising the three post-middle Campanian Plioplatecarpus species. Plesioplatecarpus, gen. nov., is erected to establish Plesioplatecarpus planifrons (comb. nov.). Further, we propose that the North American specimens referred to Platecarpus somenensis pertain to Latoplatecarpus nichollsae, based on the available phylogenetic, ontogenetic, biostratigraphic, and paleobiogeographic data and interpretations. Consequently, the current study recognizes 11 species within seven genera to constitute the Plioplatecarpinae. Of anatomical note, we suggest that quadrates in most plioplatecarpine taxa including Latoplatecarpus were tilted anteriorly in life, as a result of the suspensorial articulation forming along the distomedial portion of the long suprastapedial process that typifies quadrates in plioplatecarpine mosasaurs.

ACKNOWLEDGMENTS

We thank the following for assistance and hospitality: J. Gardner, M. Polcyn, K. Morton, J. Martin, O. Rieppel, W. Simpson, A. Shinya, W. Joyce, D. Brinkman, C. Mehling, L. Chiappe, P. Johnson, N. Bardet, and P. Godefroit. We thank G. Bell for discussions about everything mosasaur, M. Everhart for specimen photographs, O. Mateus for an electronic version of Antunes (1964), and M. Reichel for Portuguese-English translations. Comments from J. Lindgren, J. Jagt, and F. O’Keefe greatly improved the manuscript. This research was funded by an Alberta Ingenuity Fund PhD Student Scholarship (no. 200500148) to T.K., and an NSERC Discovery Grant (no. 238458-01) and Chair's Research Allowance to M.C.

Handling editor: F. Robin O’Keefe