One of the rarest of marine reptiles is the mosasaur genus Globidens , characterized by a massive, bulbous dentition. The rarity of the taxon, coupled with the bulbous dentition, resulted in various theories concerning life habits. Although a consensus indicates that the dentition was adapted for crushing resistant elements, hypotheses have varied concerning prey, ranging from turtles or bivalves to scavenging. Finally, a partial skeleton of Globidens has been recovered from the Big Bend area of the Missouri River in central South Dakota. The specimen was discovered in the upperDeGrey Formation (upperCampanian) of the Pierre Shale Group. During analysis, bivalve fragments were found packed within the rib-cage region of the skeleton. In the field, bivalve concentrations did not occur laterally or above or below the skeleton, indicating that they were the stomach contents of the mosasaur. Associated within the stomach area are a number of bivalve taxa, including oysters and small bivalves with lamellar shells, probably of the genus Anomia . The most common specimens within the stomach area are bivalves that exhibit a prismatic shell microstructure typical of inoceramids. Four inoceramid shell morphotypes were recovered, including a coarse-ribbed morphotype, a fine-ribbed morphotype, one with a thickened umbo, and a large, flat, thin-shelled morphotype. Because of their position in the mosasaur, their fragmented condition, limited taxonomic diversity, and absence from surrounding sediments, the bivalves are considered stomach contents. Some smaller, complete shells of Anomia escaped breakage, whereas larger inoceramids were invariably crushed. Chondrichthyan teeth were found associated but are interpreted to be the result of scavenging. This specimen of Globidens appears to have had a preference forthe large, flat, relatively thin-shelled inoceramids that contained a large, fleshy visceral mass.

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.