Oldest Recognized Pachycephalosaur Fossil Found in Mongolia

Meet the Oldest Dome-Headed Dinosaur Ever Discovered

By Jack Tamisiea edited by Andrea Thompson

Anybody who has ever flipped open a dinosaur ebook is probably going conversant in pachycephalosaurs. These dome-headed dinos are sometimes depicted ramming the tops of their bowling-ball-like skulls into predators or rivals.

But regardless of their recognition, pachycephalosaurs proceed to puzzle paleontologists partly as a result of fossils of those bipedal herbivores are uncommon, says Lindsay Zanno, a paleontologist at North Carolina State College. “The exception is their cranial domes, which have been virtually indestructible and are often all we discover of those critters,” she says. Nearly all of those cranium caps date again to the Late Cretaceous, when pachycephalosaurs have been already established throughout the Northern Hemisphere, obscuring the group’s early evolution.

A pachycephalosaur skeleton that was not too long ago found in Mongolia is poised to lastly fill within the lacking chapter of this dinosaur clade’s early historical past. The remarkably full fossil, which Zanno and her colleagues described on Wednesday within the journal Nature, represents a new species that’s the oldest identified dome-headed dinosaurs.

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The fossil was unearthed in 2019 in Mongolia’s Gobi Desert, a famed hotbed for dinosaur fossils. Whereas surveying a hillside, Mongolian paleontologist Tsogtbaatar Chinzorig of North Carolina State College and a co-author of the brand new paper, found the highest of a dinosaur’s noggin protruding of a cliff.

The fossil was embedded inside rocks that date to between 115 million and 108 million years in the past, within the Early Cretaceous interval, when the realm was lined by a lush river valley. The group deposited the exceptional discover on the Mongolian Academy of Sciences’ Institute of Paleontology, the place Tsogtbaatar can be affiliated.

Because the researchers chipped away on the surrounding rock, they shortly realized that the brand new specimen represented probably the most full pachycephalosaur fossil ever found. Along with the rounded cranium, the skeleton incorporates the primary report of a pachycephalosaur hand and an entire tail lined with petrified tendons. It even preserves gastroliths—gizzard stones that the animal swallowed to assist grind plant materials in its digestive tract.

The scientists named the brand new species Zavacephale rinpoche. The species identify is the Tibetan phrase for “treasured one” and refers back to the manner the cranium resembled a rounded, polished gemstone when Tsogtbaatar found it.

Zavacephale was a pint-sized pachycephalosaur that weighed roughly as a lot as a miniature poodle. Regardless of its diminutive dimension, the animal possessed a completely developed dome and had doubtless reached sexual maturity.

Researchers have debated for many years how these dinosaurs used their signature dome. Some have argued that the rounded melons performed a job in sexual choice or that they helped species acknowledge each other. However the most well-liked interpretation is that the animals used the construction to headbutt each other, as fashionable bighorn sheep do, which is supported by fossilized cranium caps that protect lesions and different indicators of trauma.

The group concluded that Zavacephale represents the oldest identified pachycephalosaur and sure originated early on within the evolution of this weird group of dinosaurs. “It tells us that the dome head developed early in pachycephalosaur evolution and arose lengthy earlier than Zavacephale’s greater, cousins began littering the newest Cretaceous fossil report with their cranium caps,” says Stephen Brusatte, a paleontologist on the College of Edinburgh, who was not concerned within the new research.

Zavacephale’s skull had a number of noteworthy quirks, nonetheless. It was principally composed of just one cranium bone as a substitute of the 2 bones seen in later species and largely lacked the knobby horns that different pachycephalosaurs had as ornamentation. Brusatte thinks that future finds of early pachycephalosaurs might additional reveal how the group’s signature headgear developed over time.

Zanno agrees. “Zavacephale was simply a gap act,” she says, “and now we get to see extra of the present.”

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