Dome-skulled dinosaurs may have looked less like Friar Tuck and more like the Fresh Prince of Bel Air. New fossil finds suggest they may have had big bristly ornaments on their heads, and might not have butted heads like they do in the movies.
Pachycephalosaurs are a clade of dinosaurs with distinct dome-shaped skulls, and a variety of horns and bumps around the edges. That gives them a bit of a Mr Burns look, and it’s long been thought that they bonked their thick heads together in combat like modern goats or stags. In the Jurassic Park movies they’re seen denting Jeeps and even busting through stone walls.
But a new study of recent fossil finds, conducted by a consultant on that series, suggests both the look and function of their heads was different. Paleontologists Jack Horner, Mark Goodwin and David Evans examined a partial skull found in Montana in 2011, and determined that it belonged to a new species of pachycephalosaur, which they named Platytholus clemensi.
It’s long been thought that the outer surface of these dinosaur’s heads was covered with a layer of keratin, the tough material found in fingernails, bird beaks and dinosaur horns. But if that was the case, the blood vessels in the bone would spread out near the surface. Instead, CT scans and microscopic studies revealed a network of blood vessels that ran vertically towards the surface of the bone and stopped.
“What we see are these vertical canals coming to the surface, which suggests that there might be keratin on top, but it’s oriented vertically,” said Horner. “I think these pachycephalosaurs had something on top of their head that we don’t know about. I don’t think they were just domes. I think there was some elaborate display on top of their head.”
The team says these head ornaments could have looked like long bristles, giving the species more of a flat top 'haircut.' This could have been brightly colored to attract mates or intimidate rivals, similar to modern birds.
But the scientists say they probably weren’t used for butting heads. The skull doesn’t have the cushioning or other internal structures that would protect the brain from damage, which are seen in living animals that settle their differences that way. In fact, the team argues that there’s no evidence that any pachycephalosaur species engaged in head-butting.
That said, this poor specimen did seem to have suffered a head injury of some kind, and lived long enough afterwards for it to begin healing. A gouge about 1.3-cm (0.5-in) deep can be seen in the dome, with clear signs of fracture and partial healing.
“We see probably the first unequivocal evidence of trauma in the head of any pachycephalosaur, where the bone was actually ejected from the dome somehow and healed partially in life,” said Goodwin. “We don’t know how that was caused. It could be head-butting – we don’t dispute that.”
On the other hand, it could have been almost anything, from a falling rock to another dinosaur. The team says it’s far from a smoking gun of head-butting behavior, given the lack of other biological evidence.
The scientists plan to conduct CT scans and microscopic studies on the skulls of other pachycephalosaur species, to investigate further.
The research was published in the Journal of Vertebrate Paleontology.
Source: UC Berkeley