Conceptual drawing of what might have happened to cause this fossil
Klug et al./Swiss Journal of Paleontology

About 174 million years ago, on what was probably an otherwise pleasant day, a lobster realized it was being eaten by a squid who, in turn, realized it was being eaten by a shark. And then they died … according to this fossil.

The fossil was found in Germany, and it took a good dose of sleuthing before scientists could determine exactly what it was showing 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 was interspersed with the belemnite’s terrifying hooks. What stumped the scientists was that the shark seemed to be completely absent. Another team of scientists argued in this paper that the fossil was really the remainder of a large marine predator’s meal.

The backbone of that argument is based on another well-preserved fossil of just such a shark from that same time period, which is housed in the Staatliches Museum für Naturkunde Stuttgart (SMNS). Inside that fossil are roughly 200 belemnite shells, the same creature found in this fossil (and in countless other large sea creatures, like ichthyosaurs and marine crocodiles). Ancient crustacean parts have also been associated with belemnites.

The fossil of the crustacean and squid
Klug et al./Swiss Journal of Paleontology

Christian Klug, lead author of the paper and curator of the Paleontological Institute and Museum at Zurich University, mentioned how difficult it was to properly interpret the fossil. “I first thought there were two crustaceans and that they perhaps scavenged on the belemnite carcass. But then it turned out that all the pieces belonged to one crustacean. The mode of preservation then led to the conclusion that it is a molt. It is known from several cephalopods that they love eating molts (for reasons us humans won’t understand). Hence, it was quite likely that the belemnite was nibbling on the empty shell.”

Adiël Klompmaker, who is the curator of paleontology at the Alabama Museum of Natural History, University of Alabama, discussed how rare soft-tissue preservation is and argued “one may argue that the softest parts of the belemnite simply decayed prior to fossilization without needing the predation event by a large vertebrate as an explanation. However, the rostrum and arms are not aligned, but are oriented at an unnatural right angle. Moreover, some soft tissue such as muscles of the belemnite are actually preserved, yet much of the rest of the soft tissue is missing. Both points argue against preservation as an explanation and favor the predation idea.”

Klompmaker then debates over whether the crustacean was a molt, or merely corpse leftovers, “The more edible, less calcified parts of the crustacean, which may have been targeted by the belemnite, are gone. If correct, the belemnite actually may have caught a living (or recently dead) crustacean on or near the ocean bottom, did not pay close attention to its surroundings as a result, and subsequently got caught by a large vertebrate predator. It probably happened close to the ocean bottom, because that is where the lobster lived and the fact that both ends of the belemnite, the rostrum and the arms, are preserved very close to each other, which would be less likely had it happened high in the water column. Thus, the slab with the fossils may represent a double act of predation, which is so rare! The vertebrate predator may have intentionally left the rest of the belemnite because it is less edible or the predator got distracted itself.”

Diagram of the identifiable fossil fragments
Klug et al./Swiss Journal of Paleontology

Paleoichthyologist Allison Bronson, who studies ancient fish at Humboldt State University, agrees with these findings. She noted to Gizmodo in an email, “Sharks are intelligent animals, and just like a living shark might mouth something to figure out if it’s edible, this fossil shark probably decided the soft bits of the belemnite were good, but this large, hard rostrum wasn’t worth ingesting.” She also mentioned how sharks today often reject things they tried to eat, like hagfish or an angel shark.

These attempted meal remnants are more formally called traces. Scientists decided to coin a new term, pabulite, to describe these types of partially-eaten ichnofossils. The word comes from the Latin pabulum (which means food) and the Greek lithos (meaning stone). Bronson notes, “What’s remarkable about this, to me, is that it’s fossil evidence of a decision. Whether this was a large shark or a bony fish that tried to eat this Passaloteuthis (we can’t know without some fossil teeth or evidence of bite marks, really) that animal made a decision not to continue ingesting the prey item.”

Several pabulites are documented in fossil records, but only a bare few are actually described in papers and put on display in a museum. How’s that for some food for thought?

via Gizmodo