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The partial skull of Texacephale, as viewed from the top. From the Cretaceous Research paper.

In the entire history of life on earth, there was nothing quite like the pachycephalosaurs, or the “bonehead” dinosaurs. These herbivorous, bipedal dinosaurs were most recognizable by the array of bumps, knobs, and spikes on their reinforced skulls, and a newly discovered species of this kind of dinosaur might help explain the origins of this group.

Described by paleontologists Nicholas Longrich, Julia Sankey and Darren Tanke in the journal Cretaceous Research, the approximately 75-million-year-old dinosaur is primarily represented by parts of its nose and its heavy skull dome. In fact, this part of the pachycephalosaur skull was so sturdy that it is often all that is found of them, and though the specimens from Texas were originally referred to a different genus, the paleontologists eventually determined that they were from a new species they called Texacephale langstoni. It lived alongside the hadrosaur Kritosaurus, the horned dinosaur Agujaceratops, tyrannosaurs, the giant crocodylian Deinosuchus and other creatures, but what really makes this new form significant is its relationship to other pachycephalosaurs.

When the scientists compared Texacephale to other similar dinosaurs, they found that it was situated near the base of the pachycephalosaur family tree. This suggests that in some ways it might be more like the earliest members of the group than the more familiar forms like Pachycephalosaurus and Stygimoloch, and if this is the case it may mean that the group originated in North America. Although the authors state that this hypothesis is tentative, it would rearrange the pachycephalosaur family tree so that the flat-headed species from Asia, which were previously thought to represent what early pachycephalosaurs were like, would instead represent specialized varieties which evolved after the group spread to that continent. This, added to the recent discovery that pachycephalosaur heads might be drastically restructured as they age, means that further research will be likely to shake up the pachycephalosaur family tree.

Longrich, N., Sankey, J., & Tanke, D. (2010). Texacephale langstoni, a new genus of pachycephalosaurid (Dinosauria: Ornithischia) from the upper Campanian Aguja Formation, southern Texas, USA Cretaceous Research, 31 (2), 274-284 DOI: 10.1016/j.cretres.2009.12.002