Mosasaurs preying upon echinoids

Eggs for breakfast? Analysis of a probable mosasaur biting trace on the Cretaceous echinoid Echinocorys ovata Leske, 1778

Christian Neumann and Oliver Hampe

What data were used?

The authors examined over 7000 specimens of Echinocorys for this study. Echinocorys is an extinct (no longer living) group of echinoids, commonly known as sea urchins or sea biscuits! Specimens were obtained from field excursions by the authors as well as examination of multiple museum collections. From examining such a large number of specimens they were able to identify many different types of predation traces but focused on the extraordinary bite traces for this study.

Methods

Each of the tooth imprints was measured as well as careful measurements of the test (body) of Echinocorys. Images of the trace (tooth imprints) were taken at various angles to visualize the structures in greater detail. A bite experiment was conducted by creating resin models of possible predator skulls with movable jaws. The skull could then simulate biting into modeling clay versions of Echinocorys. The resulting traces were measured and compared to those found in the real samples of Echinocorys.

Results and Discussion

Figure containing the images of the bite marks on the echinoid. The top part of the echinoid was not preserved so we are seeing the bottom side only, note the anus has been labeled and is not one of the punctures! (c) shows us the fine detail of where the echinoid healed the puncture wounds!

The results of this study indicate that the biting trace pattern was produced by a predator with large cone-shaped teeth that were arranged in a forward pointing direction. This was interpreted from the strange pattern in the traces. Two bite punctures are smaller and oval in outline where as two others are circular and larger, this is likely due to the angle at which the teeth made contact with the echinoid test (body).

The fact that the bite did not destroy the echinoid skeleton is quite interesting and could be interpreted as the attacker’s skillful prey handling and biting mechanics. Also, echinoid tests are very well structured, built from a series of meshwork structures that help reinforce the skeleton. This makes echinoid tests more difficult to crush compared to other invertebrate organisms such as snails or clams. Even though this echinoid sustained large punctures, it was able to begin to heal as evidenced by the newly developed skeletal material within the punctures seen in the figure above. This is not uncommon in echinoderms and has been well documented through time, quite amazing creatures!

The authors compared the bite punctures to other known predation traces in echinoids and found that it was not similar to those previously documented. They made comparisons to teeth shape, size, and when specific animals lived to attempt to identify the maker of these traces. The authors then used experimental methods with their resin models and clay-modeled echinoids to better determine the probable trace maker and found that it is most likely a globidensine mosasaur. This is from the teeth shape, pattern, time period they lived in, and experimental method to indicate the angle of teeth as they penetrated the echinoid.

This figure shows us the detail of the forward facing teeth matching up with the punctures on the echinoid test (body). In (c) we see the part of the echinoid not preserved in the fossil record.

Why is this study important?

This study represents the first likely record of mosasaur predation on echinoids. Mosasaurs were apex predators but were also opportunistic predators, as evidenced by this study. They didn’t just eat the most filling prey but also nibbled on those smaller animals that were shelly and lived on the seafloor.

The big picture

Predator-prey interactions can be observed today in a variety of environments and habitats but in the fossil record we are limited by what ecosystem interactions are preserved through time. Trace fossils are particularly useful in gaining a better understanding of how organisms interacted with one another in the past! It’s often quite difficult to gain a full understanding of the organism that left the trace since all we have is evidence of the behavior but this work provided a thorough examination of possible trace makers and even provided an experimental test to further support their idea!

Citation

Neumann, C. and Hampe, O. 2018. Eggs for breakfast? Analysis of a probable mosasaur biting trace on the Cretaceous echinoid Echinocorys ovata Leske, 1778. Fossil Record, v. 21, p. 55-66, doi: 10.5194/fr-21-55-2018

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