August 31 , 2016

by CBC News

Of all the dinosaurs that roamed prehistoric Alberta, this plant eater has earned a particular reputation for being a real butthead.

As part of the summer-long series Backyard Dinosaurs — which will feature a different dinosaur found in Alberta each week — University of Alberta paleontologist Scott Persons told CBC Edmonton's Radio Active how scientists came to that conclusion.

The critter in question is called Stegoceras, a lizard-like plant-eater that lived in herds about 77 million years ago.

Although it was only about as tall as the average first grader, Persons said they were small but mighty.

Its most prominent feature was an armoured skull, which allowed the Stegoceras to bash head-long into predators or to ram head-to-head with other dinosaurs in competitions for territory or mating rights.

"It has what looks like a crash helmet," Persons said. "Right on the top of the dinosaur's head was a big dome of bone, several inches thick.

"It gave the dinosaurs a kind of skull-cap appearance. That bulging skull roof is thought to have protected Stegoceras from shattering its own skull when colliding head-on with rivals."

"It's a dramatic image to think of two bull Stegoceras in rut, snorting at each other and then whacking heads together, like two modern bighorn sheep."
Crash test

And that theory was recently put to a rigorous crash test.

Researchers X-rayed the skull of Stegoceras and the skulls of several modern animals, including those that frequently butt heads, such as muskoxen, and other less "headstrong" animals.

From this data, 3-D computer models of the skulls were created.

Using virtual experiments, researchers were able to show that Stegoceras had what it took to endure head-on collisions.
A burley build

And it wasn't just their skulls that were built for battle.

Persons said their bodies were compact and stout, and their tails were just as strange and powerful as their heads.

"Connective tissues around the muscles in the tail that are normally soft were ossified in pachycephalosaurs, meaning they were made of bone," Persons said

"That turned the inside of the tail into a solidly reinforced structure. It may have been that, when butting heads, these dinosaurs relied on their tails in the same way that many monitor lizards do when they rear-up and wrestle with each other, or the way that kangaroos do when kick-boxing."
A bone to pick

Stegoceras fossils are extremely rare, with the exception of their skull domes.

"The domes were unappetizing to predators and scavengers, and some of the same mechanical properties that made pachycephalosaur domes good at absorbing the shock of a head-butt impact also made them resistant to weathering and erosion."

In fact, Persons said the University of Alberta's paleontology collection has drawers filled with skull domes, but only one skeleton.

http://www.cbc.ca/news/canada/edmonton/dino-of-the-week-stegoceras-1.3726505