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Named By: T. E. Carr & T. D. Williamson in 2002
Time Period: Late Cretaceous, 73 Ma
Location: Canada, Alberta - Horsehoe Canyon Formation. USA, Montana - Hell Creek Formation, New Mexico - Kirtland Formation
Size: Uncertain due to lack of fossil remains
Diet: Herbivore
Fossil(s): Partial skull domes
Classification: | Chordata | Reptilia | Dinosauria | Ornihischia | Marginocephalia | Pachycephalosauridae |

Sphaerotholus is a genus of pachycephalosaurid dinosaur from the Upper Cretaceous of the western United States and Canada. To date, three species have been described: the type species, S. goodwini, from the Den-na-zin Member of the Kirtland Formation (Late Campanian) of San Juan County, New Mexico, USA; S. buchholtzae, from the Hell Creek Formation (Late Maastrichtian) of western Carter County, Montana, USA; and S. edmontonense, from the Horseshoe Canyon Formation of Alberta, Canada. The etymology of Sphaerotholus is a combination of the Greek sphaira, meaning "ball", and tholos, meaning "dome", and is a reference to the characteristically dome-shaped pachycephalosaurian skull. The survival of Sphaerotholus from the Campanian of New Mexico to the end of the Maastrichtian of Montana demonstrates that this taxon had both a relatively long duration (approximately 7-8 million years) and a widespread distribution. Williamson and Carr, who first described the genus in 2002, diagnose it as follows: "Differs from all other pachycephalosaurids where known in the possession of a parietosquamosal bar that decreases in depth laterally as seen in caudal view and is bordered by a single row of nodes and one lateroventral corner node." Sphaerotholus is considered a highly derived pachycephalosaur.

Read more about Sphaerotholus at Wikipedia
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