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

ABSTRACTMOR 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 <i>Plioplatecarpus marshi</i> and <i>P. houzeaui</i>. However, based on the following autapomorphies, a new taxon, <i>Plioplatecarpus peckensis</i>, 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.http://zoobank.org/urn:lsid:zoobank.org:pub:3F2E8116-0190-4BEB-98B2-56A767379D98SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP