The fossil was found in Germany and it took a lot of detective work before scientists could determine exactly what it showed them. Scientists immediately recognized parts of the fossil as belonging to a belemnite — an ancient sea creature that resembles a squid — including two large hooks, hundreds of smaller hooks and the torpedo-shaped shell known as the rostrum.
Scientists were also able to quickly identify the crustacean’s claws, which alternated with the belemnite’s fearsome hooks. What baffled the scientists was that the shark appeared to be completely absent. Another team of scientists argued in this paper that the fossil was actually the rest of a large marine predator’s meal.
The backbone of that argument is based on another well-preserved fossil of such a shark from the same period, which is housed in the Staatliches Museum für Naturkunde Stuttgart (SMNS). Inside that fossil are about 200 belemnite shells, the same creature found in this fossil (and in countless other large sea creatures, such as ichthyosaurs and saltwater crocodiles). Ancient parts of crustaceans have also been associated with belemnites.
Christian Klug, lead author of the paper and curator of the Paleontology Institute and Museum at the University of Zurich, said how difficult it was to properly interpret the fossil. “At first I thought there were two crustaceans and maybe they were preying on the belemnite carcass. But then it turned out that all the pieces belonged to one crustacean. The method of storage then led to the conclusion that it is molting. Several cephalopods are known to love to eat molts (for reasons we humans won’t understand). So it was very likely that the belemnite was nibbling on the empty shell.”
Adiël Klompmaker, curator of paleontology at the Alabama Museum of Natural History, University of Alabama, discussed how rare soft tissue preservation is, arguing: “It could be argued that the softest parts of the belemnite simply decay prior to fossilization without the need for of the predation event by a large vertebrate as an explanation. However, the rostrum and arms are not aligned, but are at an unnatural right angle. In addition, some of the soft tissue, such as the muscles of the belemnite, is preserved, but much of the rest of the soft tissue is missing, both points argue against conservation as an explanation and advocate the idea of predation.”
Klompmaker then debates whether the crustacean was a molt or just remains of a corpse: “The more edible, less calcified parts of the crustacean, which may have been the target of the belemnite, have disappeared. the belemnit may have caught a live (or recently dead) crustacean on or near the ocean floor, as a result, not paying close attention to the environment and then caught by a large vertebrate predator.It probably happened close to the ocean floor, because that’s where the belemnit lived. lobster and the fact that both ends of the belemnite, the rostrum and arms, have been preserved very close together, which would be less likely if it were high in the water column, so the fossil record may be double predation, which is so rare! The vertebrate predator may have deliberately left the rest of the belemnite because it is less edible or the predator was itself distracted.”
Paleoichthyologist Allison Bronson, who studies ancient fish at Humboldt State University, agrees with these findings. She noted in an email to Gizmodo: “Sharks are intelligent animals, and just as a living shark can put something in its mouth to find out if it’s edible, this fossil shark probably decided that the soft bits of the belemnite were good, but this big, hard podium was not worth taking.” She also mentioned that sharks today often reject things they try to eat, such as hagfish or an angel shark.
These attempted meal scraps are formally called traces. Scientists decided to coin a new term, pabulite, to describe these types of partially eaten ichno fossils. The word comes from the Latin ‘pabulum’ (meaning food) and the Greek ‘lithos’ (meaning stone). Bronson notes, “What’s remarkable about this, to me, is that the fossil is evidence of a… decision. Whether this was a large shark or a bony fish trying to eat this Passaloteuthis (we really can’t know without fossil teeth or traces of bite marks) that animal has made a decision not to continue ingesting the prey item.”
Several pabulites have been documented in fossils, but only a few are actually described in newspapers and on display in a museum. How’s that for some food for thought?