What was Eric's last supper?

What did the most complete, opalised vertebrate fossil in Australia eat? In an Australian first, PhD candidate Joshua White, Dr Matthew McCurry (Australian Museum) and Aleese Barron and Professor Tim Denham (The Australian National University) used a micro-CT scanner to examine the stomach contents of the Australian Museum’s ‘Eric the plesiosaur'. Learn how the authors reconstructed this unique marine reptile’s diet.

On display in the Westpac Long Gallery of the Australian Museum is one of the most valuable and unique fossils ever discovered in Australia. The near complete, opalised plesiosaur (Umoonasaurus demoscyllus), informally known as Eric, was unearthed in 1987 from the opal mines of Coober Pedy. Named after a song from the comedy group Monty Python, Eric is a marine reptile from the Early Cretaceous inland sea of South Australia. Rather than falling into the hands of private collectors overseas, which would have made scientific studies difficult, Eric was saved by members of the public and ultimately donated to the Australian Museum. Now, PhD student Joshua White has published a study, with help from Aleese Barron, Tim Denham and Matt McCurry, using cutting edge technology to analyse Eric and confirm what its last meal may have been.

Part of what makes Eric scientifically valuable and rare is its stomach contents – the remains of its diet are preserved, giving us an insight into what this unique plesiosaur ate. Traditional methods of describing fossilised stomach contents, and therefore understanding an animal’s diet, involve examining the exterior surface for contents. This approach can be difficult and is limited, due to the rarity of fossilised stomach contents, and there can be more hidden beneath the surface that palaeontologists cannot see. It is nearly impossible to identify what is beneath the surface without destroying the fossil. However, in this study, the authors examined the internal morphology of Eric’s stomach contents using one of The Australian National University’s micro-computed tomography (micro-CT) scanners.

By using a micro-CT scanner, Joshua was able to look inside Eric’s digitised stomach contents and visualise the remains without doing any damage to the fossil. Joshua was able to identify 17 near complete fish vertebrae and 60 gastroliths (stomach stones) in Eric’s remains. The team was then able to identify the fish remains to the order Teleosti, which encompass approximately 96% of all living species of fish. Unfortunately, the team were unable to identify the fish to genus or species level due to the lack of features on the vertebrae. However, identifying the gut contents of Eric to this degree would not have been possible using traditional methods.

Using the power of the micro-CT scanner, the authors generated high resolution 3D models of Eric’s stomach, which aided in reconstructing its diet and the diet of fossil taxa more generally. Reconstructing the diet of marine reptiles' is important as it allows palaeontologists to observe their evolution through time. As environments changes, so do a marine reptile’s diet and understanding these changes can be used to predict how modern-day whales and dolphins will respond to current and emerging climate challenges. The results of Joshua’s study demonstrate the utility of CT techniques and what they can do to help infer the diet of other extinct marine reptiles around the world.

Joshua White, PhD candidate, The Australian National University and Australian Museum Research Institute.