Incredible Fossil shows a Sea Monster in the Belly of an even larger Sea Monster

Artist's interpretation of the encounter

Artist’s interpretation of the encounter
Illustration: Jim Cooke / Gizmodo

As Jedi Master Qui-Gon Jinn once said, “There’s always a bigger fish.” Or in the case of the Triassic, there is always a larger aquatic reptile, as this incredible fossil proves.

New research published in iScience provides the oldest direct evidence of “megapredition” in the fossil record, in which an apex predator feeds on formidable prey.

The fossil, found at a quarry in Guizhou province in southwestern China, appears to have a 15-ft-long (5-meter) ichthyosaur (pronounced “ick-thee-oh-sore”) shortly after partying on a 12- foot- long (4-meter) thalattosaur. Unfortunately, the ichthyosaur apparently died shortly after his meal, after biting more than he could.

Ichthyosaurs were dolphin-like aquatic reptiles that originated during the Triassic. This particular specimen belonged to an ichthyosaur species, known Guizhouichthyosaurus tangae, which grew to 33 feet (10 meters). The presumed prey, called a thalattosaur species Xinpusaurus xingyiensis, was more lizard-like, with four limbs using it to paddle through the water. The new fossil is the first direct evidence that at least suggests that some species of ichthyosaurs were as preachers of apex, similar to orcs today.

Illustration showing the shape and relative size of the animals involved.

Illustration showing the shape and relative size of the animals involved.
Image: Da-Yong Jiang, et al, iScience

The nearly complete fossil, dating to 240 million years old, suggests that the ichthyosaur struck an animal that was not much smaller than itself, in what turned out to be a fatal decision. Prior to this discovery, scientists had “never found articulated remains of a large reptile in the stomach of giant predators from the age of dinosaurs, such as marine reptiles and dinosaurs,” explained Ryosuke Motani, a co-author of the study and a paleontologist at the University of California, Davis, in a UCD press release. Prior to this discovery, scientists thought that ichthyosaurs fed exclusively on fish and kephalopods.

“Finding an animal other than fish or squid in the stomach contents of an ichthyosaurus is incredibly rare – and in fact, finding fish or inks in the stomach of the ichthyosaurus is also very rare,” said Dean Lomax, a paleontologist at the University of Manchester who was not involved in the new study, said in an email. “Only a handful of other different species of animal have been found in the stomach of an ichthyosaur as food, so the discovery of a fairly large ichthyosaur with a relatively very large thalattosaur diner is quite unusual.”

Lomax knows a thing or two about fossils embedded in fossils. Back in 2018, he was co-author of a research paper describe a pregnant ichthyosaur fossil with several unborn boys still in its ribs.

“One of the most important things about specimens like this is that they provide absolutely unique and direct information about the behavior of long-extinct species,” Lomax said. “It’s easy to assume that X feeds on Y, but if you have evidence like this, there’s no guesswork left.”

The ichthyosaur specimen with its stomach contents visible as a body protest.

The ichthyosaur specimen with its stomach contents visible as a body protest.
Image: Ryosuke Motani

It is not clear if the new fossil is an example of predation or odor, the authors admit. Scavenging, however, does not seem likely, given the evidence; limbs tend to fall off decomposed bodies before the tail falls off. In this specimen the opposite is seen: the limbs of the thalattosaur are still attached to its body, but the tail is missing. Unfortunately, paleontologists found the fossilized, detached tail of this creature only a few feet away, which according to the authors could have been lost during his fateful encounter with the ichthyosaur. However, new evidence suggests that this ichthyosaur species, or hunter as scavenger, consumed large meals, which was not previously known.

That the tail was found nearby seems almost too good to be true, so we asked Lomax what he thought.

“Your point about the tail has also piqued my curiosity, although it really seems so,” he said. ‘It did interest me, however, because the authors remark that the’ predator probably died shortly after eating the prey. ‘ They refer to this by assuming that an isolated tail of a thalattosaurus was from the same individual consumed by the ichthyosaur. If this is correct, it could suggest that the predator had bitten more than it could chew, in the sense that it was a much larger meal than he had expected and that could have led to its demise. ”

It is difficult to know exactly why the ichthyosaurus died, but if we assume that this interpretation is correct – that the isolated tail belongs to the same thalattosaurus – then the death of the ichthyosaurus could be linked to its whole meal, Lomax explained.

Another possibility is that the two sea urchins died on top of each other, and the fossils were simply assembled. And indeed, the thalattosaur fossil shows no signs of being degraded by stomach acid, but, to be honest, this observation also makes sense when considering the favorite hypothesis: that the ichthyosaur died shortly after swallowing the thalattosaur.

Image with the teeth of the ichthyosaur.

Image with the teeth of the ichthyosaur.
Image: Jiang et al. / IScience

The discovery sheds new light on the dietary habits of ichthyosaurs, which were thought to feed entirely on copphalopods because of their small, peg-like teeth. The new evidence suggests otherwise – that these teeth were used to grab prey, break spines and tear meat apart.

“Now, we can seriously consider that they ate large animals, even when they had teeth,” Motani explained in a press release from Cell Press. ‘It has been previously suggested that a cutting surface may not have been crucial, and our discovery does indeed support that. It is quite clear that this animal could process this large food with blunt teeth. ”

Modern apex predators such as orcas and leopard seals apply similar predatory tactics, in what is a possible example of convergent evolution. And indeed the ichthyosaur itself is the poster child for convergent evolution, where unrelated species evolve similar physical characteristics. Ichthyosaurs are typically compared to dolphins, but as new research shows, a more accurate comparison could be with killer whales.