Researchers say this strange, dome-headed, bristle-bristling dino from 68 million years ago has traces of keratin, what fingernails and rhino horn are made of, sticking up from its skull.
The paleontologists who discovered the beast completed a CT scan on the partially-completed skull and revealed these keratin bristles, described as giving the animal the appearance of having a “brush cut.”
The animal is called Platytholus clemensi, and is a type of pachycephalosaur discovered in 2011 in Montana’s Hell Creek Formation. It was a plant-eating dinosaur that grew up to 15 feet long and walked on two legs.
Dinosaur skulls sport an amazing variety of bony ornaments, ranging from the horns of Triceratops and the mohawk-like crests of hadrosaurs to the bumps and knobs covering the head of Tyrannosaurus rex.
There is a theory that pachycephalosaurs bashed heads in courtship rituals much like some mammals do today. But despite a gash being discovered on the skull which had healed up, the researchers say there is no real evidence to support this, and the discovery of bristles is currently considered more like an elaborate headdress.
“We don’t know the exact shape of what was covering the dome, but it had this vertical component that we interpret as covered with keratin,” said Dr. Mark Goodwin of the University of California, Berkeley. “A bristly, flat-topped covering biologically makes sense. Animals change or use certain features, particularly on the skull, for multiple functions.”
The head wound is about half an inch deep but it could have been caused by anything from a falling rock to a chance encounter with a tree or another dinosaur.
“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 Dr. Goodwin. “We don’t know how that was caused. It could be head-butting—we don’t dispute that.”
However his colleague and co-author of the paper describing the curious animal, Dr. John Horner at the University of California, Orange, believes that since Dinosaurs’ closest living relatives are birds, they should look at skull ornamentation among them, rather than their distant lizard precursors as a guide for what the purpose of these bristles was.
“That’s the first place everybody wants to go—let’s crash them together. And, you know, we just don’t see any evidence of it, histologically,” said Dr. Horner. “Any features, any accouterments that we find on the heads of dinosaurs, I think, are all display—it’s all about display.”
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He said that reptiles and birds, the closest relatives to dinosaurs, have head ornamentation for display and rarely butt heads like mammals such as sheep. While crocodiles bash their heads together over territorial and mating disputes, sometimes for hours, dinosaurs diverged from crocodiles more than 200 million years before this animal was living.
Pachycephalosaurs also lack a pneumatic chamber above the braincase, as found in bighorn sheep, which protects their brain from injury.
“I don’t see any reason to turn dinosaurs into mammals, rather than just trying to figure out what they might be doing as bird-like reptiles,” Dr. Horner said.
The study in the Journal of Vertebrate Paleontology said that blood vessels in the skull ended abruptly at the surface of the dome, indicating that the blood originally fed some tissue that was sitting atop the dome.
And as the vessels were perpendicular to the surface they most likely fed a vertical structure.
“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,” Horner continued.
“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 authors added that it could have been high, colored, or even subject to changes in color depending on the seasons. It suggests they were used for sexual display and courting, though they may have been used to butt the flanks, as opposed to the heads, of male rivals.
Dr. Goodwin said he suspects that dinosaurs likely distinguished gender by color, as do most modern birds, such as cassowaries, peafowls, and toucans, which have bright integumental colors around the face and head for visual communication.
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