If you look at enough fossils of dinosaurs, you will notice that their skulls have a remarkable variety of bony ornaments. These include the horns of Triceratops, the crests of hadrosaurs that look like mohawks, and the bumps and knobs that cover the head of Tyrannosaurus rex.
But paleontologists are finding more and more evidence that dinosaurs had even more elaborate head ornaments that were not preserved with the fossil skulls. These structures, made of fingernail-like keratin, were likely used as visual signals or semaphores to communicate with other dinosaurs of their kind.
The most recent example is a pachycephalosaur, a newly described species of dome-headed dinosaur from approximately 68 million years ago. Pachycephalosaurs tended to be small- to medium-sized plant eaters during the Cretaceous period, which occurred approximately 130–66 million years ago. Going from 3 to 15 feet in length, they strolled on two legs and had a long, firm tail for balance.
The new species depends on a halfway pachycephalosaur skull, including its bowling-ball-molded vault, that was uncovered in 2011 in the Damnation Spring Development in Montana. These are layers of Upper Cretaceous stone from which scientists have gathered dinosaur fossils for a really long time.
“What we see are these vertical canals coming to the surface, which suggests there might be keratin on top, but it’s oriented vertically, I believe these pachycephalosaurs had something on top of their heads that we don’t know about. I don’t believe they were simply domes. I believe there was some sort of elaborate display on top of their head.”
Horner, a lecturer and presidential fellow at Chapman, professor emeritus at Montana State University in Bozeman.
In view of CT examinations and minute examinations of cuts through the fossilized vault, scientists Imprint Goodwin of the College of California, Berkeley, and John “Jack” Horner of Chapman College in Orange, California, reasoned that the skull probably had worn fibers of keratin, suggestive of a brush cut.
Goodwin noted that a bristly, flat-topped covering “biologically makes sense.” “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.” Animals alter or utilize particular characteristics, particularly those on the skull, for a variety of purposes, including display or social and biological interactions that involve visual communication.
Horner, a lecturer and presidential fellow at Chapman University, professor emeritus at Montana State University in Bozeman, and emeritus curator at the Museum of the Rockies, stated, “I would guess that there was something pretty elaborate up there.”
Uniquely, the skull’s apex had a nasty gouge that had healed, indicating that the creature had survived a serious accident long enough for new bone tissue to grow into the gash.
According to Goodwin, emeritus assistant director and paleontologist at the UC Museum of Paleontology, “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.” We don’t have the foggiest idea how that was caused. We do not dispute the possibility of headbutting.
Goodwin and Horner alert that this head injury, about a half-inch down, is definitely not conclusive evidence for the celebrated speculation that these dinosaurs clashed as a feature of their social collaborations — what could be compared to the manner in which bighorn rams conflict heads today. Instead, it’s possible that the injury was brought on by anything from a rock that fell to a chance encounter with a tree or another dinosaur.
A histologically slight part of the hard domed skull of the recently portrayed pachycephalosaur The red rectangle indicates the area of injury, fracture, and partially healed bone on the dome’s top. 2 centimeters is the scale bar. Credit: Jack Horner and Mark Goodwin
“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,” Horner stated, referring to in-depth examinations of the tissues underlying the dome on both this specimen and other pachycephalosaur skulls. This man’s head was severely damaged when something struck the top of his head. Yet, having a guard component on your head is definitely not a smart thought, not really for anyone. Any elements, any accessories that we find on the heads of dinosaurs, I think, are all showcases— everything revolves around show.”
This type of ornamentation is common among dinosaurs’ reptile ancestors and their bird descendants; it’s utilized both to draw in mates and scare rivals. However, Horner and Goodwin have long argued that headbutting is a mammal behavior that rarely occurs in reptiles or birds and that the internal structure of pachycephalosaur skulls is not cushiony enough to allow headbutting without causing severe brain damage. Pachycephalosaur skulls, on the other hand, lack specializations like the bighorn sheep’s pneumatic chamber above the braincase or other features found in mammals that engage in violent headbutting.
According to Horner, “I don’t see any reason to turn dinosaurs into mammals instead of just trying to figure out what they might be doing as bird-like reptiles.”
The description of the new pachycephalosaur that was written by Horner, Goodwin, and David Evans of the Royal Ontario Museum in Canada and the University of Toronto was published last month in the Journal of Vertebrate Paleontology. The new species was given the name Platytholus clemensi by the team in honor of the late William Clemens, a paleontologist at UC Berkeley. Clemens collected a lot of fossils, especially mammalian ones, in the Hell Creek Formation, where the new species was found.
‘A bowling ball in the fossil record’
As per Horner and Goodwin, pachycephalosaur skulls are very normal in numerous dinosaur beds, but fairly less so in the Damnation Rivulet Development, which dates from the late Cretaceous time frame, a couple million years before the space rock or comet influence that brought down the shade on dinosaurs and steered life on the planet. The large bony dome is one major reason why skulls are so common.
Goodwin advised, “When thinking about pachycephalosaurs, think about a bowling ball in the fossil record.” Their skulls move around and get buried, but when they are exposed to the elements, they are very strong and can withstand a lot of weathering and erosion. Throughout the summer, people have walked over an area and discovered, more than once, that what they thought was just a rock turned out to be a beautiful dome because it looked like glacial cobble.”
Even though Goodwin and Horner have found a lot of other fossils in the Hell Creek Formation over the past 45 to 50 years, like the bones of Triceratops, T. rex, and duck-billed hadrosaurs, they are most interested in pachycephalosaurs—their evolution and how they changed from being young to adults. They have sliced through a lot of skulls to see how they change over time and to test the idea that the animals butted heads, or at least that the males did.
Their verdict: Based on the structure of the bones, there is no evidence that the skull or neck could withstand a head-to-head collision. The recently depicted halfway skull, which was not found with different pieces of the skeleton, likewise has a bone design conflicting with head-butting.
Since the skull bones didn’t seem to be examples from any of the other two kinds of adolescent, sub-grown-up, or grown-up pachycephalosaurs that lived nearby around a similar time — Pachycephalosaurus itself, after which these dinosaurs are named, and Sphaerotholus — the scientists characterized the creature as another family and species, Platytholus clemensi.
The well-organized vertical arrangement of the neurovascular network in Platytholus clemensi’s skull and dome on a computed tomography (CT) scan suggests that the network fed verticle structures on top of the dome. The scale bar is two centimeters. Credit: Mark Goodwin and Jack Horner
The skull did have some features that paleontologists had seen in other pachycephalosaurs, like Sphaerotholus: veins in the skull that finished unexpectedly at the outer layer of the vault, showing that the blood initially took care of some tissue that was sitting on the arch. In the event that that covering were a sheath of keratin, the veins would have fanned out and left spaces or notches along the domed surface, as seen, for instance, under the mouths of birds or on the skulls of Triceratops and different ceratopsians or horned dinosaurs. However, as if they were feeding a vertical structure, the vessels were perpendicular to the surface.
According to Horner, “What we see are these vertical canals coming to the surface, which suggests that there may be keratin on top, but it’s oriented vertically.” I think these pachycephalosaurs had something on top of their heads that we have close to zero familiarity with. They weren’t just domes, according to me. I believe some elaborate display was placed on top of their head.”
Goodwin noted that pachycephalosaurs’ domed heads changed shape as they got older, becoming more prominent and elaborate as they got closer to adulthood. That, as well, would suggest they were utilized for sexual presentation and pursuit; however, they might have been utilized to butt the flanks, instead of the heads, of male adversaries. He thinks that dinosaurs probably knew their gender by color, like most modern birds, like cassowaries, peafowl, and toucans, who use bright colors around their faces and heads to communicate visually.
“It’s sensible to recommend that the covering over the vault may likewise have been splendidly shaded or liable to variety change occasionally,” he said.
Paleontologists are taking CT scans and doing thin-section histology on other pachycephalosaur domes to see if, in addition to the known array of bumps, nodes, and horns, other dome-headed dinosaurs may have had elaborate vertical headgear.
“The blend of cranial histology after flimsy segmentation of the skull and CT filtering provided us with a lot more extravagant collection of information and structures, which is a reason for our speculation that there was a keratinous covering over the vault,” Goodwin said. “In contrast to Triceratops, T. rex, and other dinosaurs, which had hard skin or keratin closely covering the bone, we hypothesize, at least in this taxon, that the dome was covered with something.”
Goodwin and Horner named the new species after Clemens in light of the fact that both grew close connections to him over the many summers every one of the three investigated Montana looking for Cretaceous fossils, once in a while working next to each other in the field.
According to Horner, “Bill Clemens was a very important person in Mark’s life, but he may have been more important in my life because he was the one who, in 1978, said, “You know, Jack, there’s this woman in Bynum, Montana, who found a large dinosaur, and she needs it identified.” Horner stated that the woman also inquired about a few smaller fossils in her rock shop when he and his colleague Bob Makela visited, which turned out to be “the first baby dinosaur bones found in the world.”
That revelation gave the primary obvious proof that a few dinosaurs really focused on their young and drove Horner to compose a few books about family structure among duckbilled dinosaurs, including “Digging Dinosaurs” in 1988 and a continuation, “Dinosaur Lives: Uncovering a Transformative Adventure,” in 1997. Additionally, he wrote several books for children, including “Maia: A Dinosaur Grows Up,” a 1995 film about a baby Horner duckbill named Maiasaura, and “Lily and Maia…a Dinosaur Adventure,” a 2023 sequel.
“I owe a lot of appreciation to Bill Clemens for sending me on that little outing,” said Horner.
More information: John R. Horner et al, A new pachycephalosaurid from the Hell Creek Formation, Garfield County, Montana, U.S.A., Journal of Vertebrate Paleontology (2023). DOI: 10.1080/02724634.2023.2190369
