Palaeontologists have discovered the skeleton of an enormous 240 million year old reptile, which has the contents of its last meal – an almost equally massive sea creature – still visible in its stomach. The finding suggests that megapredation, which is the eating of large animals by other large animals, was more common in the ancient Triassic period than previously believed.
The bones of the larger creature, which belongs to a family of marine reptiles called ichthyosaurs, were first discovered in the Guizhou province of China in 2010. In its day, the ichthyosaur was likely an apex predator, and fossilized remains suggest that some species could grow up to a monstrous 26 m (85 ft) in length, making them comparable to the blue whales that inhabit today’s oceans.
While the ichthyosaur breathed air like modern-day whales and dolphins, its body shape was closer to that of a tuna. This strange leviathan was also carnivorous, and the new research reveals just how ambitious a mouthful these ancient terrors were willing to take down.
Following the discovery of the ichthyosaur Guizhouichthyosaurus in China, palaeontologists noted that the almost 5-m (15-ft)-long fossil had a large bulge in the stomach containing a mass of smaller bones.
Upon closer inspection, scientists were able to identify the remains as those of a slightly smaller reptile species known as a Xinpusaurus xingyiensis, which belonged to a group of four-limbed, lizard-like creatures called thalattosaurs.
"We have never found articulated remains of a large reptile in the stomach of gigantic predators from the age of dinosaurs, such as marine reptiles and dinosaurs," comments Ryosuke Motani, professor of Earth and planetary sciences at the University of California, Davis, and co-author on the new paper. "We always guessed from tooth shape and jaw design that these predators must have fed on large prey but now we have direct evidence that they did."
The partial remains of the thalattosaur, which account for the trunk, or middle of the reptile along with its four rudder-like legs, are among the longest ever found inside the belly of a prehistoric marine reptile.
There are two possible explanations as to how the head and tail of the smaller reptile got detached from the body. Over time, they may have simply fallen off as the connecting muscles decayed, presenting a huge but manageable mouthful for the roaming ichthyosaur. Alternatively, the larger predator could have forcibly ripped the body apart before consuming it.
The researchers believe that predation is the more likely cause for the ancient maiming rather than decay, as elements of the thalattosaur's limbs that would ordinarily have been among the first to decay and break away from the body were instead found inside the belly of the larger reptile.
Furthermore, it is unlikely that a marine predator would eat the head and tail of the kill and leave the nutritious trunk floating in the water. This suggests that it was the ichthyosaur that ripped apart and ate the thalattosaur. It is possible that the giant reptile broke the spine of its 4 meter-long prey with the force of its bite, before proceeding to tear it apart, using a similar strategy to modern day orcas.
If this is the case, the new find represents the oldest direct evidence of marine megapredation – or large animals eating other large animals – in the Triassic period.
The remains of the thalattosaur were left relatively undamaged by the stomach acid of the larger predator, suggesting that the ichthyosaur died and was fossilized almost immediately after consuming its final meal.
The paper has been published in the journal iScience.
Source: University of California, Davis