CT scans taken of skull of ‘not very bright’ dinosaur

A small plant-eating dinosaur’s skull has been scanned to reveal that it had a unique combination of sensory traits which today are found in animals that spend at least part of their time underground.

The results of the innovative scans are published in Scientific Reports.

It is the first time such behaviour has been associated with a dinosaur by analysing its sensory capabilities.

The scanned specimen is nicknamed Willo – a 3.6-metre-long Thescelosaurus neglectus housed at the North Carolina Museum of Natural Sciences. Willo would have weighed about 340 kilograms and lived just before the extinction event at the end of the Cretaceous period (145–66 million years ago) which is known as the end of “The Age of Dinosaurs”.

Thescelosaurus were herbivores, and not particularly bright – even by dino standards. Their scientific name roughly translates to “wonderful overlooked lizard”.

“The irony is that palaeontologists generally think of these animals as pretty boring,” says co-author Dr Lindsay Zanno, associate research professor at North Carolina State University and head of palaeontology at the museum. “When we first looked at our results we thought, yeah, this animal is plain as toast. But then we took a big step back and realised there was something unique about the combination of Willo’s sensory strengths and weaknesses.”

Using CT scans of Willo’s skull, the researchers were able to compare the creature’s brain size and shape to those of living animals to determine what Willo’s senses of smell, hearing and balance were like.

Thescelosaurus hearing was limited – only about 15% the range of human hearing, or 4–7% the range of cats and dogs. It was especially bad at hearing high-pitched sounds.

The low-frequency sounds that Thescleosaurus was best at hearing overlap with the sounds that palaeontologists believe Tyrannosaurus rex would have produced.

“This doesn’t tell us they were adapted to hearing T. rex vocalise, but it certainly didn’t hurt them to know when a major predator was tooling about in the area. More interesting to us was the fact that these particular deficiencies are often associated with animals that spend time underground,” Zanno says.

It’s poor hearing and lack of smarts was offset by a powerful sense of smell.

“They were relatively larger than those of any other dinosaur we know of so far, and similar to those of living alligators, which can smell a drop of blood from miles away,” says lead researcher Dr David Button – a former Brimley Postdoctoral Scholar at the North Carolina Museum of Natural Sciences and North Carolina State University. 

“Thescelosaurus may have used its similarly powerful sense of smell to instead find buried plant foods like roots and tubers. It also had an unusually well-developed sense of balance, helping it to pinpoint its body position in 3D space, another trait often found in burrowing animals.”

The animal had powerful arms and legs – traits also present in burrowing animals.

“While we can’t say definitively that these animals lived part of their lives underground, we know that their ancestors did,” Button says. “This fact, together with their unique combination of sensory abilities, strongly suggests T. neglectus engaged in similar behaviours.”

“We still don’t know the sensory abilities of most dinosaurs,” Zanno says. “That makes it difficult to link these traits to specific lifestyles with confidence, but it also means there are plenty of cool discoveries to come. No matter what, we now know for certain that T. neglectus isn’t boring.”