X-ray analysis sheds new light on prehistoric predator's last meal

The researchers used micro-CT scans to peer inside the fossilised stomach remains of a small marine reptile -- a plesiosaur nicknamed 'Eric' after a song from the comedy group Monty Python -- to determine what the creature ate in the lead up to its death.

The researchers were able to find 17 previously undescribed fish vertebrae inside Eric's gut, confirming the plesiosaur's diet consisted mostly of fish -- reinforcing findings from previous studies conducted in 2006.

The findings could help scientists learn more about the evolutionary history of extinct organisms such as Eric, as well as help predict what the future might look like for our marine life. According to the researchers, the study demonstrates the potential to use x-rays to reconstruct the diets of other extinct organisms that inhabited Earth hundreds of millions of years ago.

"Previous studies examined the exterior surface of Eric's opalised skeleton to find clues," PhD researcher Joshua White, from the ANU Research School of Physics and the AMRI, said.

"But this approach can be difficult and limiting as fossilised stomach contents are rare to find and there can more hidden beneath the surface that would be near impossible for palaeontologists to see without destroying the fossil.

"We believe our study is the first in Australia to use x-rays to study the gut contents of a prehistoric marine reptile.

"Our research employed very powerful x-rays to help us see the animal's stomach contents in never-before-seen detail, including finding fish bones in its gut.

"The benefit of using x-rays to study these prehistoric animals is that it does not damage the fossil, which is incredibly important when dealing with valuable and delicate specimens such as Eric."

Mr White sifted through mountains of data and CT imagery to differentiate between what he believed to be evidence of fish bones, gastroliths, also known as stomach stones, and other materials that the reptile had consumed. The data was used to create a 3D model of Eric's gut contents.

"Eric was a mid-tier predator, sort of like a sea lion equivalent, that ate small fish and was likely preyed upon by larger, apex predators," Mr White said.

"We are also lucky in the sense that Eric is one of the most complete opalised vertebrae skeletons in Australia. The fossil is approximately 93 per cent complete which is pretty much unheard of in any fossil record.

"There is practically nowhere else other than Australia that can actually get opalised vertebrae fossils."

The ANU scientists say learning more about the diet of extinct organisms is an important step in understanding their evolutionary past, but it can also help us understand how animals alive today might be impacted by things such as climate change.

"As environments change, so too does a marine reptile's diet and understanding these changes can be used to help predict how animals of today will respond to current and emerging climate challenges," Mr White said.

"If there's any change to an animals' diet, we want to look at why this change occurred and by some measure we can compare this to modern animals such as dolphins or whales and try to predict how their diets might change due to climate change and why."

Eric was first discovered in the opal mines in Coober Pedy in South Australia in 1987. The prehistoric predator is on display at the Australian Museum in Sydney.