A marine reptile called an ichthyosaur ripped into the feeding torso of a slightly smaller marine reptile 240 million years ago, swallowed it and died away, according to a new study.
© Jiang et al.
This image shows a close-up of the stomach area of the ichthyosaur.
The animal and its stomach contents fossilize and preserve the remains of the other animal, called a thalattosaur.
This discovery provides the best evidence yet of megapredition, which is when large animals prey on other animals that are the size of humans or larger.
“We have 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,” said Ryosuke Motani, study co-author and professor of earth and planetary sciences at the University of California Davis.
© Ryosuke Motani
This image shows the ichthyosaur specimen with its stomach contents visible as a block extruding from the body.
“We’d 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 study was published Thursday in the journal iScience.
Ichthyosaurs were almost dolphin-like marine reptiles that first appeared in the Earth’s oceans 250 million years ago. They had bodies that were structurally similar to fish, such as tuna, but needed to breathe air the way modern dolphins and whales do.
© Jiang et al.
This image shows the teeth of the ichthyosaur.
They were probably the apex predators – the predators at the top of the feather chain of their environment – as orca and great white sharks are in the oceans today. But real evidence to determine who the apex predators were in prehistoric times is challenging.
Therefore, it was significant when an almost complete fossil of an ichthyosaur, Guizhouichthyosaurus, was found in a quarry in Guizhou province of China in 2010. Inside the fossil’s stomach was an interesting bulge of other bones.
An analysis showed that this cluster of fossils belonged to another marine reptile, the thalattosaur Xinpusaurus xingyiensis. Thalattosaurs were much more than lizards and used their four limbs to help them paddle through the water.
The ichthyosaur measured about 15 feet long, and the thalattosaur, though lean, was still 12 feet long.
When the ichythyosaur consumed the thalattosaur, he licked his torso, including front and hind legs, hard. Nearby, researchers found the fossil of the tail of the thalattosaur.
Determining a megapreditor
The thalattosaur represents one of the longest fossils ever in the stomach of a fossilized marine reptile. So what happened that led to it becoming the meal of a marine reptile that was only slightly larger?
© Da-Yong Jiang, et al / iScience
This graph shows the fossil and compares the size of the two marine reptiles.
At first glance, the ichthyosaur did not look like a large predator. It had small teeth resembling pins, better adapted to help it grip animals similar to squid. Usually, sharp teeth with cutting edge are a requirement to cut into other large prey.
In this scenario, the ichthyosaur probably used his teeth to grab the thalattosaurus, potentially breaking his back, and then rip apart in the way modern orca, crocodiles and leopard seals do.
There is also the possibility that the ichthyosaurus detected an already dead thalattosaurus, but the researchers do not believe that this is the case here.
Based on studies of decaying creatures in marine environments, the limbs of the thalattosaur would loosen first. Instead, they were still attached to the torso inside the ichthyosaur’s stomach. Meanwhile, the tail, which would later loosen when he was already dead, was disconnected from the body yard away from the “crime scene.” This suggests that the tail was ripped by the ichthyosaur.
“Our finding suggests that megapredition was probably more common among ichthyosaurs than we previously thought,” Motani said.
Earlier, other evidence, such as the size and the fact that three species of ichthyosaurs had sharp, sharp teeth, suggested that they may be apex predators.
What killed this ichthyosaur?
“The stomach contents of our ichthyosaurus were not etched by stomach acid, so it must have died out pretty well after eating this food,” Motani said.
The researchers can only use the facts they have to share why the ichthyosaur died so quickly after eating the thalattosaur.
The thalattosaur, which lacks its head and tail, showed no signs of being digested by the ichthyosaurus.
Meanwhile, the ichthyosaur’s neck is broken, although its head and body remain intact.
They estimated that the thalattosaurus was unusually large for its species.
The broken neck of the ichthyosaur shows its cause of death because it could not inhale and there could be multiple causes of the fracture.
The ichthyosaur may have trouble separating the head or tail from the thalattosaurus, swallowing its massive torso as the thalattosaurus may have fought back by twisting and rocking, Motani said.
It probably did not help that the neck vertebrae of the ichthyosaur were narrower compared to the rest of his body. But the true cause of death is based solely on speculation.
If the team saw the site of the fossil, which was moved about a kilometer from the rock growth to the Geopark Museum, still excavated, the researchers discovered new things. They want to determine how environments had changed at the time this marine life existed and what enabled them to move in the open sea.
“There are so many things to do,” Motani said. “We have more specimens from the rock growth waiting for us to study them.”
“The quarries provide the earliest records of marine reptiles with open sea – marine reptiles first colonized the coastal waters about 10 million years earlier and were finally ready to expand into open sea by this time.”
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