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Visions of prehistoric life are big on violence and drama. The struggle between predator and prey, as well as fights between rivals, are classic fodder for envisioning the deep past. When we see teeth, claws, spikes, and armor, we can’t but imagine what they were used for. But these savage moments were not the whole of the prehistoric world. An unusual find from Germany is a reminder of calmer Mesozoic moments.
The fossil, described by paleontologist Dean Lomax and colleagues, records a few continuous moments of Jurassic time laid out in limestone. The story is easy to follow. Thin, parallel lines make up most of the fossil, stretching over 28 feet. And at the very end of that drag mark, there rests the shell of the ammonite Subplanites rueppellianus.
The ammonite drag mark. Credit: Lomax et al 2017
If the ammonite had been alive when it left the drag, then this would count as a trace fossil – imprints and other signs of the behavior of living animals. In this case, however, Lomax and colleagues point out that the Subplanites was probably dead when it made the drag. When these ammonites were killed and rapidly buried, they would preserved the hardened lower jaw. In this case, the Subplanites lacked the lower jaw, indicating that it must have fallen out during decay. In fact, the gases produced inside the shell as the cephalopod rotted likely gave it just enough buoyancy to be carried a long way over the ancient seafloor.
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Lomax and coauthors conclude their paper by writing that “MCFO 0492 represents the hitherto longest fossil drag mark created by a dead animal, complete with the animal preserved at the end.” It can’t tell us anything about the behavior of Subplanites. But along with other drag, bounce, and roll marks, fossils like these still offer us a window into a lost world. If you were able to dip back into the Jurassic seas and knell on the bottom, but you probably wouldn’t be surrounded by a feeding frenzy. More likely, you’d see an expired ammonite idly drifting by, leaving us a reminder that the fossil record is about more that nature red in tooth and claw.
Reference:
Lomax, D., Falkingham, P., Schweigert, G., Jiménez, A. 2017. An 8.5 m long ammonite drag mark from the Upper Jurassic Solnhofen Lithographic Limestones, Germany. PLOS ONE. doi: 10.1371/journal.pone.0175426
