A new species of Plioplatecarpus (Mosasauridae, Plioplatecarpinae) from the Bearpaw Formation (Campanian, Upper Cretaceous) of Montana, U.S.A.

ABSTRACT

MOR 1062 is a plioplatecarpine mosasaur that is represented by a nearly complete skull, complete cervical series, and partial dorsal vertebral column. The specimen, collected from Upper Cretaceous (Campanian) deposits of northeast Montana, exhibits a pristine level of preservation, yielding morphological details not typically observed. Phylogenetic analysis recovers MOR 1062 within an unresolved trichotomy with Plioplatecarpus marshi and P. houzeaui. However, based on the following autapomorphies, a new taxon, Plioplatecarpus peckensis, sp. nov., is erected to accommodate this suite of features exhibited by MOR 1062: a narrow, elongate prenarial portion of the premaxilla that is constricted at midlength; a maxilla with a nearly straight narial margin in lateral view; a short prefrontal lamina of maxilla that contributes to a very low profile of the snout immediately anterior to orbits; a suspensorial ramus of parietal that does not rotate into horizontal plane distally; nine or 10 pterygoid teeth; an otosphenoidal crest that covers the exit for cranial nerve VII in lateral view; jugular and condylar (= hypoglossal) foramina that exit separately; axial spine with a distinctly notched dorsal border; hypapophyseal peduncles on postcranial vertebrae 2–7; and hypapophyses 2–5 bearing paired, anteriorly projecting knobs.

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ACKNOWLEDGMENTS

We greatly thank J. Horner and P. Roath for access to MOR 1062, thereby enabling its study. M. Polcyn provided pictures of elusive mosasaur lacrimals. Special acknowledgment goes to P. Druckenmiller for assisting with access to the specimen and for stimulating discussion. Thanks also to M. Caldwell, T. Konishi, H. Maddin, and A. Palci for discussions relating to mosasaurs, and K. Brink and J. Mallon who assisted with logistics in transporting the specimen. Finally, our gratitude goes to M. Polcyn and an anonymous reviewer for helpful and constructive reviews of the manuscript, and J. Conrad for his work as handling editor.