In June, 2008, the partial internal mold of a small ammonite was discovered beneath a Tylosaurus nepaeolicus skull collected from the Clioscaphites vermiformis-C. choteauensis zone (early to mid-Santonian), Smoky Hill Chalk. in northern Lane County, Kansas by staff of the Rocky Mountain Dinosaur Resource Center. The specimen was collected and later donated to the Sternberg Museum of Natural History. The ammonite did not appear to be directly associated with the vertebrate remains. The mold preserves a trace of the siphuncle as distinct line visible for about 4 cm along near the outer edge of the specimen. Although incomplete, the specimen preserves the distinctive uncoiled form of a heteromorph ammonite, and appears to be quite similar to a species (Glyptoxoceras texanum) recently named from Santonian deposits in northeastern Texas. This specimen is the first known occurrence of a heteromorph ammonite in the Smoky Hill Chalk.