Paleontologists have discovered a plant-eating dinosaur that live 70 to 80 million years ago. The new species, Texacephale langstoni,  was about as big as a medium sized dog. The discovery represents a new genus of pachycephalosaur, a group of bipedal, thick-skulled dinosaurs.

Researchers discovered two skull fragments in Big Bend National Park in southwest Texas in 2008 and compared them to dozens of fossils from related species found in Canada and Montana.

The new species is one of about a dozen known to have solid lumps of bone on top of their skulls, which researchers speculate was probably used to ram one another head-on in a manner similar to modern-day musk oxen and cape buffalo.

(Photo Credit: Nicholas Longrich/Yale University)

The discovery of the new species lends further weight to the idea, which has gained popularity in recent years, that dinosaurs found in Canada and the northern United States were distinct from their southern neighbors.

"Instead of roaming across the North American continent, we see pockets of different dinosaurs that are pretty isolated from one another," said Nicholas Longrich of Yale University. "Every time we get good fossils from Texas, they end up looking very different from those to the north."

Because fossils from the Big Bend region are rare and tend to be poorly preserved, scientists do not have a complete picture of the different species that once inhabited the area.

But the team may have uncovered an important piece of the puzzle with their discovery. They found that this particular group of dinosaurs, which was previously thought to have originated in Asia, likely evolved in North America.

Longrich expects more related species to be discovered in the future as fossils from the Texas site and elsewhere continue to be examined.

Texacephale langstoni had softball-sized lumps of bone on top of their skulls. Researchers found two of the fossilized domes in Big Bend National Park in southwest Texas.

(Photo Credit: Nicholas Longrich/Yale University)

Citation: Nicholas R. Longricha, Julia Sankey, Darren Tanke, 'Texacephale langstoni, a new genus of pachycephalosaurid (Dinosauria: Ornithischia) from the upper Campanian Aguja Formation, southern Texas, USA', Cretaceous Research, April 2010, 31(2) April 2010, 274-284; doi:10.1016/j.cretres.2009.12.002