Fossil vertebrates are extremely rare in the Fort Hays Limestone member of the Niobrara Chalk in comparison to the rich variety of well-preserved fish, turtles, mosasaurs, pteranodons, and toothed birds collected from the overlying Smoky Hill Chalk, and to a lesser extent, the underlying Carlile Shale. Although mosasaurs are well documented from the Smoky Hill Chalk (Upper Coniacian – Lower Campanian), and occur rarely in the Carlile Shale (Middle Turonian), they had not been previously reported from the intervening Fort Hays Limestone (Lower Coniacian). Here we report the remains of a mosasaur (FHSM VP-2297) preserving 14 articulated vertebrae, the left coracoid, ribs, and fragments of sternal cartilage collected by M.V. Walker in 1967 from Ellis County, Kansas. Serrated bite marks on several of the ribs are attributable to the anacoracid shark, Squalicorax falcatus, and suggest postmortem scavenging of the remains. The specimen is identified as Tylosaurus sp. on the basis of the characteristic shape of the coracoid and represents the earliest documented occurrence of that genus. It is also the first record of a mosasaur in the Fort Hays Limestone and preserves the earliest evidence of scavenging on mosasaur remains by Squalicorax.