The skull is dome-shaped, however UC Berkeley and Chapman University paleontologists think it was covered with bristles of keratin (purple) that may have been even more elaborate than depicted here. The bony knobs and spikes (yellow) are particular of pachycephalosaurs and many other dinosaurs.
CT scans indicate that particular pachycephalosaurs had detailed structures on their domes.
If you look at enough dinosaur fossils, youll see the amazing variety of bony ornaments embellishing their skulls, from the frightening horns of the Triceratops to the mohawk-like crests of the Hadrosaurs and the plethora of bumps and knobs identifying the head of the Tyrannosaurus Rex.
Paleontologists are discovering increasing evidence suggesting that dinosaurs boasted even more complex head designs not maintained in the fossilized skulls. These structures, made from keratin– the same material as human fingernails, were likely used as visual signals or semaphores to others of their kind.
A newly explained species of dome-headed dinosaur– a pachycephalosaur dating from around 68 million years back– is the most current example. Pachycephalosaurs lived throughout the Cretaceous duration, in between about 130 and 66 million years back, and tended to be small-to-medium-sized plant eaters. Ranging from 3 to 15 feet long, they walked on 2 legs and had a long, stiff tail for balance.
The bony knobs and spikes (yellow) are characteristic of pachycephalosaurs and numerous other dinosaurs. A freshly explained types of dome-headed dinosaur– a pachycephalosaur dating from around 68 million years earlier– is the latest example. Any functions, any accouterments that we find on the heads of dinosaurs, I think, are all display– its all about display screen.”
Such ornamentation is typical in the reptile forefathers of dinosaurs and their bird descendants; theyre utilized both to attract mates and frighten competitors. He presumes that dinosaurs likely identified gender by color, as do most modern birds, such as peafowls, toucans, and cassowaries, which have bright integumental colors around the face and head for visual interaction.
The brand-new types is based upon a partial pachycephalosaur skull, including its bowling-ball-shaped dome, that was discovered in 2011 in the Hell Creek Formation in Montana, which are layers of Upper Cretaceous rock from which paleontologists have gathered dinosaur fossils for years.
Based on CT scans and microscopic analyses of pieces through the fossilized dome, paleontologists Mark Goodwin of the University of California, Berkeley, and John “Jack” Horner of Chapman University in Orange, California, concluded that the skull likely had actually sported bristles of keratin, reminiscent of a brush cut.
A histological thin area of the bony domed skull of the freshly explained pachycephalosaur. The area of injury, fracture and partly recovered bone on the top of the dome is revealed by the red rectangle. (The scale bar is 2 centimeters). Credit: Jack Horner and Mark Goodwin
” We dont understand the precise shape of what was covering the dome, however it had this vertical part that we analyze as covered with keratin,” Goodwin stated, noting that a bristly, flat-topped covering “biologically makes sense. Animals alter or use particular features, especially on the skull, for numerous functions– it could be for display screen or for biological and social interactions involving visual communication.”
” I would think that there was something quite elaborate up there,” stated Horner, a speaker and governmental fellow at Chapman, professor emeritus at Montana State University in Bozeman and emeritus manager at the Museum of the Rockies.
Peculiarly, the skull had a nasty gouge at the apex that had healed, showing that a serious mishap once befell the creature, but that it had made it through long enough for new bone tissue to turn into the gash.
” We see most likely the very first unquestionable proof of trauma in the head of any pachycephalosaur, where the bone was actually ejected from the dome in some way and healed partly in life,” said Goodwin, emeritus assistant director and paleontologist at the UC Museum of Paleontology. “We dont know how that was caused. It might be head-butting– we do not contest that.”
Goodwin and Horner caution that this head lesion, about a half-inch deep, is not a smoking weapon for the storied hypothesis that these dinosaurs butted heads as part of their social interactions– the Cretaceous equivalent of the method bighorn rams clash heads today. Rather, the injury could have been brought on by anything from a falling rock to a possibility encounter with a tree or another dinosaur.
A CT scan of the dome exposes the well-organized vertical plan of the neurovascular network in the skull and the dome of Platytholus clemensi, recommending that the network fed verticle structures on top of the dome. (Scale bar is 2 centimeters). Credit: Jack Horner and Mark Goodwin
” Thats the first location everyone desires to go– lets crash them together. And, you know, we just do not see any evidence of it, histologically,” Horner said, describing comprehensive research studies of the tissues underlying the dome, both in this specimen and in other pachycephalosaur skulls. “Something hit the top of this guys head and harmed it, and it was something that was extreme. Having a defense mechanism on your head is not a great concept, not for any person. Any functions, any accouterments that we find on the heads of dinosaurs, I believe, are all show– its all about display.”
Such ornamentation prevails in the reptile forefathers of dinosaurs and their bird descendants; theyre utilized both to draw in mates and daunt rivals. However Horner and Goodwin have long argued that the internal structure of pachycephalosaur skulls is not cushiony sufficient to permit head-butting without extreme mental retardation, and that head-butting is a mammal thing that is seldom seen in birds or reptiles. Particularly, pachycephalosaur skulls lack expertises, such as a pneumatic chamber above the braincase, as found in bighorn sheep, or other functions present in mammals that take part in violent head-butting behavior.
” I do not see any reason to turn dinosaurs into mammals, instead of just trying to figure out what they may be doing as bird-like reptiles,” Horner stated.
Horner, Goodwin, and David Evans of the University of Toronto and the Royal Ontario Museum in Canada published their description of the new pachycephalosaur last month in the Journal of Vertebrate Paleontology. The group named the brand-new types Platytholus clemensi, after the late UC Berkeley paleontologist William Clemens, who gathered numerous fossils– in specific mammalian fossils– in the same Hell Creek Formation where the brand-new species was found.
A bowling ball in the fossil record
According to Horner and Goodwin, pachycephalosaur skulls are quite typical in numerous dinosaur beds, though somewhat less so in the Hell Creek Formation, which dates from the late Cretaceous Period, a few million years before the asteroid or comet effect that decreased the drape on dinosaurs and altered the trajectory of life in the world. One main factor for the skulls universality is the big bony dome.
” With pachycephalosaurs, think about a bowling ball in the fossil record,” Goodwin stated. “Their skulls roll around, get buried, and when exposed on the surface, theyre really robust, so they can endure a lot of weathering and erosion remaining there. More than once, people have walked over an area all summer season and found that what they thought was simply a rock, because it appears like a glacial cobble, ended up being a truly good dome.”
Goodwin and Horner have uncovered numerous other fossils from the Hell Creek Formation over the past 45 to 50 years, including bones of Triceratops, T. rex, and duckbilled hadrosaurs, they have a specific interest in pachycephalosaurs– both their development and their advancement from juvenile to adult. Theyve sliced through numerous skulls to study how they alter in time and to check the theory that the animals butted heads with one another, or a minimum of, that the males did.
Their conclusion: Theres no proof, based upon bone structure, that the skull or neck might endure a head-to-head collision. The newly explained partial skull, which was not found with other parts of the skeleton, also has a bone structure irregular with head-butting.
Since the skull bones didnt appear like specimens from any of the other two kinds of juvenile, sub-adult, or adult pachycephalosaurs that lived in the area around the same time– Pachycephalosaurus itself, after which these dinosaurs are called, and Sphaerotholus — the paleontologists classified the animal as a new genus and species, Platytholus clemensi.
The skull did have qualities that the paleontologists had seen in other pachycephalosaurs, including Sphaerotholus: capillary in the skull that ended quickly at the surface of the dome, indicating that the blood initially fed some tissue that was sitting atop the dome. If that covering were a sheath of keratin, the blood vessels would have spread out and left indentations or grooves along the domed surface area, as seen, for example, under the beaks of birds or on the skulls of Triceratops and other ceratopsians or horned dinosaurs. The vessels were perpendicular to the surface area, as if they fed a vertical structure.
” What we see are these vertical canals coming to the surface, which suggests that there might be keratin on top, however its oriented vertically,” stated Horner. “I think these pachycephalosaurs had something on top of their head that we dont understand about.
Goodwin noted that the shape of the domed heads of pachycephalosaurs changed as the animals grew, ending up being more intricate and prominent as they approached adulthood. That, too, would recommend they were used for sexual display screen and courting, though they may have been used to butt the flanks, instead of the heads, of male rivals. He suspects that dinosaurs likely differentiated gender by color, as do most contemporary birds, such as toucans, peafowls, and cassowaries, which have bright integumental colors around the face and head for visual communication.
” Its reasonable to recommend that the covering over the dome may also have actually been brilliantly colored or based on color modification seasonally,” he said.
The paleontologists are obtaining CT scans and doing thin-section histology of other pachycephalosaur domes to figure out whether other dome-headed dinosaurs may have shown intricate vertical headgear in addition to the known range of horns, nodes, and bumps.
” The combination of cranial histology after thin-sectioning the skull and CT scanning gave us a much richer body of data and forms a basis for our hypothesis that there was a keratinous covering over the dome,” Goodwin stated. “We understand the dome was covered with something, and we make a hypothesis, a minimum of in this taxon, that it had a vertical structural element, unlike Triceratops, T. rex, and other dinosaurs, which had difficult skin or keratin closely covering the bone.”
Goodwin and Horner called the new species after Clemens due to the fact that both developed close ties to him over the many summers all 3 checked out Montana in search of Cretaceous fossils, often working side by side in the field.
” Bill Clemens was a really important person in Marks life, but he might have been more crucial in my life due to the fact that he was the individual who, back in 1978, said, You understand, Jack, theres this woman in Bynum, Montana, who found a large dinosaur, and she needs it identified,” Horner stated. When he and associate Bob Makela had a look at the females rock store, Horner said, she asked about a couple of smaller sized fossils in her shop, too, which turned out to be “the very first baby dinosaur bones discovered worldwide.”
That discovery offered the very first clear evidence that some dinosaurs looked after their young and led Horner to compose numerous books about family structure among duckbilled dinosaurs, consisting of Digging Dinosaurs in 1988 and a sequel, Dinosaur Lives: Unearthing an Evolutionary Saga, in 1997. He likewise composed a number of kidss books, including Maia: A Dinosaur Grows Up, in 1995, about a baby duckbill of the types Horner called Maiasaura, and the 2023 sequel, Lily and Maia … a Dinosaur Adventure.
” I owe a fantastic amount of thankfulness to Bill Clemens for sending me on that little journey,” said Horner.
Reference: “A brand-new pachycephalosaurid from the Hell Creek Formation, Garfield County, Montana, U.S.A.” by John R. Horner, Mark B. Goodwin and David C. Evans, 14 April 2023, Journal of Vertebrate Paleontology.DOI: 10.1080/ 02724634.2023.2190369.
The work was moneyed by a Smithsonian Institution grant to Horner and grants from the National Science Foundation to Goodwin.
