Cleveland museum's dome-headed dinosaur find adds insight to dinosaur diversity

Posted May 08, 2013 in Articles

Author: John Mangels

If the new dinosaur that paleontologists Michael Ryan of the Cleveland Museum of Natural History and David Evans of Toronto's Royal Ontario Museum unveiled Tuesday hadn't been so hard-headed, they might never have found it.

Not that the animal was stubborn. Just dense up top. The crown of the 85 million-year-old animal's skull was as hefty as a Stephen King novel – a whopping two-inch-thick dome of bone.

The massive skull cap was all that remained of the otherwise slight, collie-sized dinosaur. The dome's robustness saved it from whatever ravages befell the rest of the skeleton. A graduate student working with Ryan and Evans unearthed the bone from a hillside in the southern Alberta, Canada, badlands in 2008.

After the scientists compared it with a similarly thick skull fragment in the Toronto museum's collection, they determined that the two fossils represented a previously unknown genus, or grouping, and species from the family of dome-headed dinosaurs called pachycephalosaurs. (The family name, pronounced pack-ee-SEF-ah-lo-sore, is Greek for "thick-headed lizard.")

The researchers christened their dinosaur Acrotholus audeti (ack-row-THO-lus aw-DET-eye), a combination of the Greek phrase "highest dome" and the last name of Roy Audet, the Canadian rancher on whose land they dug up the fossil. At more than 80 million years, it's the oldest dome-headed dinosaur yet found in North America, and possibly the world, the two scientists report in the online journal Nature Communications.

While the discovery of a new individual dinosaur is important, Ryan and Evans say the implications of this find are broader, hinting at a hidden, much greater variety of dinosaur types.

Fossils of small-bodied dinosaurs are relatively scarce, compared with bigger relatives like the lumbering duck-billed hadrosaurs and spiky, truck-sized ceratopsids. One interpretation is that there simply weren't as many of those smaller animals around. But an alternate explanation is that their more fragile bones crumbled or were scattered, precluding discovery. The hardy pachycephalosaur domes are an exception; nearly 500 samples of their chunky skulls have been found in North America and Asia.

Based on their analysis, Evans and Ryan contend that scientists have sharply underestimated the diversity of small, plant-eating dinosaurs like Acrotholus.

"If these other small-bodied dinosaur groups are anywhere near as diverse as we're seeing with pachycephalosaurs, they were a lot more diverse than we ever expected," said Evans, the study's lead author.

Original Article: http://www.cleveland.com/science/index.ssf/2013/05/cleveland_museums_dome-headed.html