ALLEGED MOSASAUR BITE MARKS ON LATE CRETACEOUS AMMONITES ARE LIMPET (PATELLOGASTROPOD) HOME SCARS

New data contradict the mosasaur-bite hypothesis for the origin of hol es seen in Placenticeras ammonites from the Late Cretaceous Pierre Sha le and Bearpaw Formation of the western interior of North America. Obs ervations of a limpet-infested Placenticeras ammonite and of several P lacenticeras specimens with radular scratch marks reveal that the limp ets dwelled on floating ammonites, and their homing activity produced circular depressions. When altered during diagenesis, the depressions mimic tooth punctures. Crushing experiments on fresh Nautilus shells u sing a mosasaur robot show that mosasaur bites could not have produced holes resembling those in the fossils. Furthermore, sectioning of ''b itten'' ammonites reveals that sepia are sometimes intact under the ho les, an observation irreconcilable,vith penetration by a tooth. We pre sent an alternative interpretation that the alleged ''bite marks'' in Placenticeras ammonites are really limpet home scars that were altered after burial. While predation of mosasaurs on ammonites remains a pos sibility, it would have to be demonstrated by other criteria. Our find ings do not support mosasaur-ammonoid coevolution in the Late Cretaceo us.