During the Cretaceous, dome-headed pachycephalosaurs roamed through what is now the Hell Creek Formation, covering parts of Montana, Wyoming, and North and South Dakota. But UCMP Curator Mark Goodwin and Museum of the Rockies Curator Jack Horner argue that there were fewer pachycephalosaur species than we thought. Mark and Jack suggest that two species, Dracorex hogwartsia and Stygimoloch spinifer, are actually juveniles and teenagers of the species Pachycephalosaurus wyomingensis. Learn about this modern day dinosaur extinction — read Mark and Jack's paper, published this week in the open access journal PLoS ONE, read the UC Berkeley News press release on the study, and watch this video!

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