The Niobrara Chalk in western Kansas was deposited on the eastern shelf of the Late Cretaceous Western Interior Sea during Coniacian through early Campanian time, hundreds of miles from the nearest land. As might be expected, the remains of terrestrial animals, including dinosaurs, are extremely rare in this marine environment. The first dinosaur (Claosaurus agilis) collected by Marsh from the Smoky Hill Chalk Member of the Niobrara Chalk in 1871 was also the only hadrosaur known from this formation. All other dinosaur remains collected there since 1871 have been identified as nodosaurs. Here we report the discovery of an articulated series of nine hadrosaur caudal vertebrae (FHSM VP-15824) from the Smoky Hill Chalk (Upper Coniacian) of southeastern Gove County, Kansas. The presence of non-serrated bite marks on four of the vertebrae and the partially digested appearance of the proximal and distal ends of the series suggest that the vertebrae had been scavenged from the floating carcass of a dinosaur by a large shark, most likely Cretoxyrhina mantelli. The specimen represents the earliest known occurrence (Upper Coniacian) of the Hadrosauridae in the Smoky Hill Chalk, and preserves the earliest evidence of scavenging on dinosaur remains by a shark in the Western Interior Sea.