The most complete specimen of the unusual mosasaur Globidens has been discovered in central South Dakota along the Missouri River. The specimen consists of the anterior half of a skeleton, including crushed skull, pectoral girdle, partial paddle, and vertebral series. One humerus and ulna exhibit pathologies. The partial skeleton was found at the top of the DeGrey Formation (upper Campanian) of the Pierre Shale Group and is therefore the youngest skeleton from North America. The specimen exhibits apomorphies that correspond with the late occurrence and indicate a new species. Increased dental hypsodonty, lack of a posterior buttress on teeth, great size, and massive build indicate a derived intermediate species of a clade that first occurred with rounded teeth in the early Campanian in North America and Europe (Globidens alabamaensis and Globidens dakotensis) and culminated with high-crowned teeth with posterior buttresses in the Maastrichtian of Africa, the Middle East, and South America (Globidens phosphaticus). Associated with the specimen are bivalves that are interpreted as stomach contents and shark teeth that are interpreted as the result of scavenging.