Meet the Oldest Dome-Headed Dinosaur Ever Found

"Anyone who has ever flipped open a dinosaur book is likely familiar with pachycephalosaurs. These dome-headed dinos are often depicted ramming the tops of their bowling-ball-like skulls into predators or rivals. Yet despite their popularity, pachycephalosaurs continue to puzzle paleontologists in part because fossils of these bipedal herbivores are rare, says Lindsay Zanno, a paleontologist at North Carolina State University."

"The exception is their cranial domes, which were practically indestructible and are usually all we find of these critters, she says. Almost all of these skull caps date back to the Late Cretaceous, when pachycephalosaurs were already established across the Northern Hemisphere, obscuring the group's early evolution. A pachycephalosaur skeleton that was recently discovered in Mongolia is poised to finally fill in the missing chapter of this dinosaur clade's early history."

Pachycephalosaurs are dome-headed bipedal herbivores often depicted ramming rivals, but body fossils are rare while cranial domes are frequent because they were practically indestructible. Almost all known skull caps come from the Late Cretaceous, leaving the group's early evolution poorly documented. A remarkably complete Early Cretaceous pachycephalosaur skeleton unearthed in Mongolia in 2019 represents a new species and is the oldest known dome-headed dinosaur, helping to fill the clade's missing early chapter. The fossil was embedded in rocks dated between 115 and 108 million years ago from a lush river valley and was deposited at the Mongolian Academy of Sciences' Institute of Paleontology.

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