Inside the head of an ankylosaur

Russian palaeontologists have studied the structure of the brain and blood vessels in the skull of the ankylosaur Bissektipelta archibaldi by making a digital cast of its braincase.

This allowed them to discover that ankylosaurs, and Bissektipelta in particular, were capable of cooling their brains, had an extremely developed sense of smell, and could hear low-frequency sounds.

But their brains were one and a half times smaller than that of modern animals of the same size, a team from St Petersburg University writes in a paper in the journal Biological Communications.

Herbivorous ankylosaurs looked a bit like a modern armadillo, with thick armour and sometimes a bony club on the tail.  They roamed the Earth from the middle of the Jurassic period – about 160 million years ago – until the end of the dinosaur era.

“If you look at dinosaurs, then ankylosaurs and their closest relatives, stegosaurs, were almost outsiders,” says lead author Ivan Kuzmin. “The mass of their brain turned out to be at least half less than what we would expect, based on a comparison with present-day animals. It was about 26.5 grams for a three-metre Bissektipelta.

“Its brain size can be compared with two walnuts. Nevertheless, ankylosaurs existed on the planet for 100 million years. They were quite successful in terms of evolution. However, judging by the size of their olfactory bulbs, they sniffed a little faster than they thought.”

A trove of uniquely preserved ankylosaur fossils was found, among other treasures, during a series of international expeditions in Uzbekistan two decades ago. Three fragments of ankylosaur braincases were the subject of the recent study.

“Thanks to the development of computer tomography over the past 15-20 years, palaeontologists are able to learn more and more about the dinosaur brain and its structure,” says Kuzmin. “We decided to re-describe Bissektipelta archibaldi, and we managed to clarify its place on the phylogenetic tree of ankylosaurs.

After meticulous work over three years, the researchers discovered that a considerable part of the dinosaur’s brain was occupied by olfactory bulbs: about 60% of the size of the cerebral hemispheres. This allowed for impressive olfaction that can even be compared with that of the famous predator Tyrannosaurus rex, they suggest.

Its hearing was quite different too. Studying the anatomy of the inner ear suggests it heard frequencies from about 300 to 3000 hertz, similar to modern crocodiles.

And then there is the interesting ability “to cool its brains in the literal sense”.

“The network of veins and arteries in its braincase turned out to be very complicated: they did not go in a single direction, but constantly communicated with each other, like a system of railway tracks,” Kuzmin says.

“The blood could have flown in different directions and been redistributed, while maintaining the optimal brain temperature of the animal. For example, if the top of an ankylosaur’s head became warm, the vessels diverted quickly the warm blood and created a screening effect – as if a dinosaur put a sun hat on.

“Moreover, the endocranial vasculature of ankylosaurs turned out to be somewhat more like the vessels of present-day lizards than that of the closer extant relatives of dinosaurs – crocodiles or birds.”