First records of plesiosaur remains in the lower Smoky Hill Chalk Member (Upper Coniacian) of the Niobrara Formation in western Kansas

Abstract

Although plesiosaurs are known to occur in the Upper Cretaceous Smoky Hill Chalk Member of the Niobrara Formation, their remains are uncommon, rarely complete and unequally distributed in the unit. There are only three reasonably complete plesiosaur skeletons (all Dolichorhynchops osborni) known from the Smoky Hill Chalk in Kansas. All three are from the upper one-third (Early Campanian) of the chalk. Other remains are fragmentary and, in most cases, consist of body parts that could have been readily removed by predators or scavengers. Many of these specimens have teeth marks or appear to be partially digested. In spite of observations to the contrary by Williston and others, reliable stratigraphic and locality information for museum specimens exists only for plesiosaur remains in the upper portions of the Smoky Hill Chalk (Santonian - Lower Campanian). Recent discoveries reported here suggest that plesiosaurs were present throughout the deposition of the chalk, albeit in small numbers.