Mosasaur Bite Marks on our Canadian Ammonites

Ammonites largest predator, a fossilized reminder of the threats in the Bearpaw Sea.

Ammonites are found on every continent, in rock formations from 400 Million to 65 Million years in age. Only in Southern Alberta, Canada however, are they found in high concentrations with these distinctly bright, beautiful and iridescent colours. This makes any Ammonite specimen with a bite mark and the Canadian iridescence a beautiful rarity.

In several cases, the KORITE team has uncovered Ammonites with distinct markings on the outer surface. Some believe these marks to be visible impressions of the Ammonites biggest predator; The Mosasaur. Alternatively, some paleontologists think they could be scrapes from small, marine snails called Limpets who were thought to attach themselves to the Ammonite Shell similar to a barnacle on a boat’s hull. The debate is considered ongoing, with strong data supporting arguments from both sides suggesting these marks could either be the remnants of Limpet scars, or bite marks of the Mosasaur or both! Some of the specimens KORITE has excavated show impression patterns matching that of a mosasaur jaw with reliable accuracy.  This evidence makes most of the team at KORITE slightly leaning towards the “Bite Mark” Camp.


In 1998 Tomoki Case from the National Science Museum in Tokyo and Paul Johnston, a close friend to KORITE and former curator of invertebrate paleontology at the Royal Tyrrell Museum and current professor at Calgary’s Mount Royal University argued that the alleged mosasaur bitemarks were in fact limpet home scars. They inspected many fossil examples of ammonites with limpets actually attached. They then built a robotic replica of a mosasaur jaw and crushed modern-day Nautilus shells to see if puncture marks on only one side of a shell could be experimentally produced. The crushed shells were examined and compared to fossil ammonites displaying marks previously credited to mosasaur bitemarks. They concluded that most were in fact limpet homing scars as they attached themselves to the outside of the ammonites. 

As a rebuttal, in 2001 Paleontologists Cameron J. Tsujita and Gerd E.g Westermann re-examined the evidence and concluded that tooth marks on ammonite shells were much more common than damage done on empty shells by limpets. After examining over 150 Placenticeras shells from Alberta, Tsujita and Westermann found that the various indentations and punctures in the ammonite shells more closely matched what would be expected of large mosasaurs rather than small, algae-eating limpets.

The debate continues…..

Shown below are a few examples of Mosasaur jaw fossils to put things into perspective. The Mosasaur had two rows of teeth, making this pre-historic sea creature a fearsome predator. As an Ammonite, it’s clear you would want to stay away from these guys.

KORITE Fossil Mosasaur JawKORITE Ammolite | Fossil Mosasaur Public Domain ImageKORITE Fossil Mosasaur Jaw

While the jury is still out on the true cause of these marks, it’s safe to say that the combination of the iridescence only found on Ammonites from Southern Alberta, alongside puncture wounds caused by Either Mosasaur or Limpets is a rare treat. We recently photographed several Ammonite specimens which are good examples of such impressions.

Korite Ammolite | Ammonite hand specimens with bite marks

Shown here is what we at KORITE feel is a visible impression of the Mosasaur tooth penetrating the fossilized ammonite. Also dubbed the ‘T-Rex of the Sea’, the Mosasaur often hunted the Ammonites around 70 Million years ago, and the results in the fossil records offer a stark reminder of the dangers the Ammonites faced.

So what do you think caused the perforations on the Ammonites over 70 Million years ago?

  1. Bite Marks
  2. Limpet’s Scars

While not all our Ammonites feature these marks, KORITE is committed to restoring, protecting, and sharing these national treasures. If you have any questions, or would like to learn more about the wonders of Ammolite or Ammonites please Contact us.

Fossil image - Diagram by Williston showing the three common mosasaurs of the Western Interior Seaway of North America. By Williston 1898 ( [Public domain], via Wikimedia Commons