Recreating fossils in 3D modelling technology could help us to understand more about the behaviour of prehistoric creatures, and in this case, we are seeing the effect of environment rather than behaviour in the fossils we find.
We usually find bones, teeth or shells, or trace fossils, such as tracks and burrows. However, the drag mark in this case has not been made by the ammonite (a popular prehistoric squid fossil found across the globe) during its life and does not reflect its behaviour. Instead, it has been created by the environment and this is an extremely rare find with an incredible 8.5 metre long drag, when in the past all we have seen is a metre or so.
The start of the drag mark is not preserved, so it may actually have been much longer, and the mark was created by contact of the ammonites’ ribs with the lagoon floor. The preserved start begins with just two lines, suggesting only two of the ammonite’s ribs were in contact with the bottom of the lagoon. The number of ribs in contact with the mud increases along the drag mark’s length, indicating the ammonite was very slowly sinking as it drifted along the bottom.
Dean Lomax studying the fossil at the Cosmocaixa Museum in Barcelona
A trace and its maker preserved together in the fossil record are rare. However, rarer still are marks created by dead animals together with the animal that made the mark. So, how did the fossil move after it had already died? Ammonites had gas chambers, which they used to control their buoyancy and movement, similar to a submarine. However, the shell of the study fossil was probably empty and some of the gas could have remained present in the shell. This meant the ammonite did not sink straight to the bottom and fall over. Instead, the ammonites’ shell was dragged along the bottom of the tropical lagoon by what must have been a calm and steady current.
Using digital and 3D modelling technologies, we created a virtual model of the fossil by compiling over 600 photographs of the specimen. We then produced a video, which shows the drag mark and the preserved ammonite. Such modern digitization techniques, like the photogrammetry method we used, can give us an excellent snapshot of an unusual moment in time and tell us more about how the environment and not just behaviour can affect fossils.
The ammonite and its 8.5m drag mark
The study specimen for the research paper, published in PLOS ONE, is a species called Subplanites rueppellianus, which was collected from the historically important Late Jurassic Solnhofen Limestones of Germany, famous for its fossil preservation.