A fossil of an ichthyosaur , a dolphin-like marine reptile, has turned up in China, and its remains have led to more interesting research than might have been expected. The paleontologists who studied the finding found that in the abdominal region and between the ribs of the fossilized animal there was a dense concentration of bones. These were morphologically different bones from the ichthyosaur skeleton. “At first, we didn’t believe it, but after spending several years visiting the dig and seeing the same specimens, we were finally able to understand what we were seeing,” Ryosuke Motani, professor of paleobiology at the University of California, commented on the study. United States). The ichthyosaur, about five meters long, had eaten a four-meter aquatic reptile. We are talking about a fossil that probably represents the oldest evidence of megafaunal predation by marine tetrapods.
Ichthyosaurs, known to many as “sea dragons” , are a group of large extinct marine reptiles that were shaped like fish. They evolved from reptiles that returned to the water after adapting to life on land. An evolutionary process like the one experienced by dolphins and whales, which is why with our current mentality we see it as similar. Ichthyosaurs were one of the largest predators of the Jurassic period. They lived from 245 million years ago to 90 million years ago, so although they lived with the dinosaurs, they became extinct about 25 million years earlier.
We have remains of ichthyosaurs with different sizes and belonging to very distant times, which is a challenge to try to unravel what they fed on. Paleontologists study their jaws and the shape of their teeth to launch hypotheses about it. It was common to think that prehistoric species that had a huge jaw with long, sharp teeth could eat other large prey. Animals capable of eating megafauna, that is, prey equal to or larger than humans, are considered megapredators . The surprise of this ichthyosaur fossil found in China is that its teeth do not meet these requirements, and yet it ate a thalattosaurus , an aquatic reptile that looks like a lizard.
The teeth of the ichthyosaur led the researchers to think of a diet based on soft prey such as cephalopods. In fact, among the analyzed fossil record, we have a baby ichthyosaur whose last meal was squid . But the discovery of this fossil can change this perception. “Now, we can seriously consider that they ate large animals, even though they had strong-gripping teeth,” Motani told SciTechDaily. Despite having blunt teeth, this prehistoric dolphin helped himself to a four-meter plate of alligator.
heavy digestion
The specimen set a new record for the size of the largest prey eaten by Mesozoic marine reptiles, bringing the previous record of 2.5 meters to 4 meters in length. Since there is barely a meter difference between the size of the predator and that of the prey, a debate was generated: did the ichthyosaur hunt the thalattosaurus, or did it simply eat a dead body?
The fossilized prey inside the ichthyosaur is missing its head and tail, raising questions about it. But the study leans more towards predation and not an act of scavenging. Among other evidence, they mention that the ends and soft parts of animals are the first to be digested, as opposed to the spine and ribs: hard parts of the prey that require long digestion. And furthermore, if a predator other than the ichthyosaur had hunted the thalattosaur, it wouldn’t make much sense for it to have left the animal’s nutritious trunk intact.
In any case, the digestion was not carried out completely. The stomach contents were not broken down by the acids that come into play during digestion, but rather the ichthyosaur must have died shortly after ingesting its huge prey.
New perception of mega predators
The study concludes that megafaunal predation may have been more widespread than previously thought. The predator had teeth for grasping rather than tearing, but that didn’t stop it from swallowing the carcass of large prey. There were many marine reptiles from the same period with similar teeth, so the possibility that they could feed on megafauna more frequently should be considered.
Of course, as is often the case in science, they are not definitive interpretations . The data of the study is limited to what is preserved in the fossil that we mention and following the knowledge that we currently have in anatomy, ecology and taphonomy.
“Before, we guessed that they must have eaten these big things, but now, we can safely say that they did eat large animals. This also suggests that mega-predation was probably more common than we previously thought,” concludes Ryosuke Motani.
References:
Jiang, D. et al. 2020. Evidence Supporting Predation of 4-m Marine Reptile by Triassic Megapredator. iScience, 23 (9) DOI: 10.1016/j.isci.2020.101347.Motani, R. 2009. The Evolution of Marine Reptiles. Evo Edu Outreach 2, 224–235 DOI: 10.1007/s12052-009-0139-y.
