Oldest bone-headed dinosaur discovered in Canada

A real bonehead! Paleontologists have discovered a new species of bone-headed, dog-size dinosaur that lived about 85 million years ago in what is now Alberta, Canada.
The new species, dubbed as Acrotholus audeti, was identified from both recently discovered and historically collected fossils.
Approximately six feet long and weighing about 40 kilogrammes in life, the newly identified plant-eating dinosaur represents the oldest bone-headed dinosaur (pachycephalosaurs) in North America, and possibly the world.
Acrotholus means "high dome," referring to its dome-shaped skull, which is composed of solid bone over 10 centimetres thick, researchers said.
Acrotholus walked on two legs and had a greatly thickened, domed skull above its eyes, which was used for display to other members of its species, and may have also been used in head-butting contests, they said.

Acrotholus lived about 85 million years ago. The new dinosaur discovery is based on two skull 'caps' from the Milk River Formation of southern Alberta.

"Acrotholus provides a wealth of new information on the evolution of bone-headed dinosaurs. Although it is one of the earliest known members this group, its thickened skull dome is surprisingly well-developed for its geological age," said lead author Dr David Evans of the Royal Ontario Museum and University of Toronto.
"More importantly, the unique fossil record of these animals suggests that we are only beginning to understand the diversity of small-bodied plant-eating dinosaurs," said Evans.

Small mammals and reptiles can be very diverse and abundant in modern ecosystems, but small dinosaurs (less than 100 kg) are considerably less common than large ones in the fossil record.
The massively constructed skull domes of pachycephalosaurs are resistant to destruction, and are much more common than their relatively delicate skeletons-which resemble those of other small plant-eating dinosaurs.
Researchers suggest that the pachycephalosaur fossil record can provide valuable insights into the diversity of small, plant-eating dinosaurs as a whole.
"We can predict that many new small dinosaur species like Acrotholus are waiting to be discovered by researchers willing to sort through the many small bones that they pick up in the field," said Dr Michael Ryan, curator of vertebrate paleontology at The Cleveland Museum of Natural History, co-author of the study.

"This fully domed and mature individual suggests that there is an undiscovered, hidden diversity of small-bodied dinosaurs," Ryan said.
The study was published in the journal Nature Communications.