A partial pliosaur skull reveals anatomical features poorly known for Plesiosauria. The specimen lacks recorded contextual information, however preservational character and nannofossil analysis (earliest Turonian) suggests origination from the upper Greenhorn Limestone. The vomers bifurcate near their posterior termination, and are overlapped by long, slender extensions of the anterior pterygoids. The latter character has only recently been noted and may be variously developed in many if not all plesiosaurs. Large foramina commonly referred to as the ‘internal nares’ are formed at the juncture of the palatines, vomers, and maxillae. Configuration of the palatal elements differs in several ways from the only well established pliosaurid taxon of the North American Cretaceous, Brachauchenius. Particular differences include a more visibly elongate and lanceolate shape of the vomers, palatines which do not project as far anteriorly (similarly for the ‘internal nares’), and a squared posterior termination of the palatines. A relatively elongate muzzle and homodont dentition differ from the shorter muzzles and caniniform teeth of Kronosaurus and Plesiopleurodon. The specimen is also not referable to the poorly founded taxon Polyptychodon. With no clearly similar material for reference, the specimen may expand the definition of Brachauchenius as currently known or could represent an undescribed taxon. Although perhaps not of taxonomic significance, the specimen is impressively large with an estimated total skull length of 1.75 m, the largest known for a North American plesiosaur.