Modern mammals, fish, and reptiles feed on squid and octopus, so it can also be concluded that ancient reptiles and fish fed on ammonites. Ammonites that exhibit bite marks are not rare, but the bite marks are often confused with broken shells. However, there have been hundreds of claims of ammonites with preserved mosasaur tooth marks since Kauffman and Kesling’s 1960’s paper on the subject. Most of these are holes bored or dissolved in the ammonite shells from limpets or other forms of gastropods, rather than holes made from the bite of a mosasaur.

The edges of the holes on this ammonite show an irregular, slightly broken shape. This is much different from the smooth, round holes caused by limpet borings. Limpets and other boring gastropods stop dissolving the shell when they get through the surface of the shell, they do not dissolve the underlying septa. This ammonite has no septa showing in any of the existing holes because the teeth of a reptile have crushed it.

This specimen is one of the finest examples of a mosasaur-bitten ammonite ever found. The holes form a perfect bite pattern, identical to the upper tooth pattern of a mosasaur named Plioplatecarpus. The tooth marks only penetrated the phragmocone of the shell, where the septa supported the surrounding shell, and did not allow for a wide scale collapse of the shell around the holes. Most of the body chamber of the Placenticeras has been bitten and broken off of the specimen, probably by the predator in an attempt to eat all of the soft fleshy parts of the ammonite.

This specimen is truly the perfect addition to any marine display, especially those showcasing marine reptiles.