An unusual type of fossilized fish can be found within the limestone of present-day Germany. The Late Jurassic era conditions exhibited at the famed Solnhofen deposits have preserved the remains of multiple marlin-like marine predators known as Aspidorhynchus.
But these carnivorous remains aren’t complete specimens—they’re decapitated heads still attached to gastrointestinal tracts. According to a study published in the journal Fossil Record, the graphic remnants often offer a look at both each fish’s final moments, as well as their last meals.
The Solnhofen limestone deposit is one of the world’s best sources of fossilized species from the Late Jurassic period (about 161.5 to 143.1 million years ago). This is especially the case for many marine creatures including Aspidorhynchus, who swam in the prehistoric Tethys Ocean. Resembling today’s swordfish or marlin, Aspidorhynchus regularly grew to over three feet long and featured a lengthy, spear-like upper jaw. They comprised roughly four percent of all known fish swimming through the Solnhofen Archipelago at the time, resulting in many fossilized examples to study.
Paleontologists Martin Ebert and Martina Kölbl-Ebert recently examined 343 Aspidorhynchus fossils from the region, noting that 16 percent of them were only the decapitated heads and attached guts. Aside from exhibiting such a strange and unique state of preservation, the examples allowed the pair to analyze the predator’s choices of prey.
“Judging from their body shape and fin morphology, it is highly likely that Aspidorhynchus was a pursuit predator. From its stomach contents, we know that it fed mainly on small teleosts (Orthogonicleithridae),” Martin Ebert said in an accompanying statement.
Teleosts are the group encompassing nearly all of today’s bony, ray-finned fish.
“There is evidence that the Orthogonicleithridae were schooling fish, and it is assumed that Aspidorhynchus, with its long upper jaw, may have used a hunting technique similar to modern swordfish,” he added.
Multiple Aspidorhynchus fossils showed the predators often swallowed juvenile teleosts whole, but they occasionally dined on much larger prey. In one case, a roughly 22-inch-long Aspidorhynchus successfully devoured a 6.3-inch-long fish. Another example revealed the presence of a small fish stuck in its mouth, which essentially caused it to drown.
But why the decapitation? The headless Aspidorhynchus’ didn’t hit a stroke of bad luck. Instead, the partial remains likely speak to how each predator ultimately fell victim to the prehistoric food chain. The study’s authors theorize that these fish were each hunted down by a larger predator. While Aspidorhynchus would usually swallow their meals in one gulp, other hunters often bit their target’s tail before violently ripping them apart using intense headshakes. The bit detaches the head, leaving the more nutritious, easily digestible bodies to eat.
The authors believe this easily explains the plethora of separated skulls and guts, while also noting the array of possible suspects behind the decapitations.
“In the Solnhofen archipelago, we know of [6.5–13 ft long] Ichthyosaurus, marine crocodiles, and even larger Pliosaurs, for whom this was certainly no problem,” said Ebert.
