A paleoartist's reconstruction of Eilenodon. It is a green lizard with ridges along its back.

A paleoartist's reconstruction of Eilenodon © Nicholls/Paleocreations.com 2018

Measuring the teeth of an ancient reptile

Scientists have peered inside the tooth of the extinct reptile Eilenodon.

Eilenodon was a plant-eating reptile that lived alongside the dinosaurs of North America during the Late Jurassic Period. It would have looked similar to a large, beefy modern-day lizard. 

Eilenodon's only living descendent is the tuatara, a reptile species today found only in New Zealand. Tuatara are rare, and of great interest to scientists, as they are the last members of the order Rhynchocephalia. Many species which belonged to this order (like Eilenodon) once lived alongside the dinosaurs. 

Neutron scanning shows the Eilenodon tooth had thicker enamel at its base than at its tip.

Neutron scanning shows the Eilenodon tooth had thicker enamel at its base than at its tip.

Many studies have been done on the teeth of mammals, however detailed examinations of reptiles' jaws are rarer. So Dr Marc Jones, an evolutionary biologist based at the Museum and the University of Adelaide, was particularly excited to be studying such a rare example of this animal's teeth.

Marc says, 'Studying teeth can tell us more about an animal's diet, developmental history and relationship to other animals.

'It was fascinating to be able to see inside this tooth and learn more about how its owner might have lived. I first saw this specimen in 2004, so I have been waiting a long time to complete this study.'

The thickness of enamel (the hard shell on the outside of a tooth) can provide an insight into how a tooth formed and what kind of material an animal eats.

An off-green coloured tuatara looking at the camera.

Tuatara are the last living descendant of Eilenodon. This one is called Henry and he lives at the Southland Museum and Art Gallery Image by KeresH via Wikimedia Commons, licensed under CC BY 3.0.

 

Eilenodon had rows of closely-packed teeth and strong jaws for chewing and shredding plants. It would have eaten a range of herbaceous plants, rushes and shrubs that were rich in protein and easy to digest, plus the occasional insect.

In a process that took 36 hours to complete, Marc and his colleagues scanned a young tooth that would have come from the left-hand side of of an Eilenodon jaw collected in Colorado, USA.

They found that the enamel inside Eilenodon's tooth was thick around the base to stop it fracturing, but thin at the tip to allow it to become sharp enough for shredding plant material.

Marc also found that this tooth differed from those of other extinct animals that were closely related to Eilenodon. For instance, it had thicker enamel than its relative Sphenodon, suggesting these animals ate different foods. 

eilenodon-tooth-image-xray-neutron-two-column

Sections of the Eilenodon tooth made using X-ray and neutron scanning

The benefits of neutron scanning

Scientists used a neutron scanner to examine the tooth, which helps to figure out what an object is made of. It allowed them to make a 3D 'map' of the enamel inside the tooth.

Researchers often use X-ray scanners to look inside a specimen. These can identify the 3D shape and internal structure of an object, and also highlight hidden details which could be missed by the naked eye.

Neutron scanners work differently from X-ray scanners, and use highly penetrating subatomic particles for imaging, instead of X-rays, which are a high-energy form of light. These particles can reveal details that are hidden, even to X-rays.

Historically, neutron imaging has been used on plant fossils, but much less so on animal fossils.

Marc says, 'X-ray CT scanning has become a very familiar tool for investigating fossils, but in this case it was not as informative as a neutron scanner. Neutrons are more effective at revealing the internal structure of this precious tooth.

‘Working with experts at the Australian Centre for Neutron Scanning felt like a real privilege.’

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