Sphaerotholus

Sphaerotholus was an advanced dome-headed pachycephalosaur that lived across North America during the Late Cretaceous epoch. Reaching an estimated length of two metres and a mass around forty kilograms, it was roughly comparable in size to a large dog. Like other members of its family, its most striking feature was a thickened cranium of solid bone, accented at the rear by a shelf of small nodular spikes. Multiple species have been named from formations ranging from New Mexico to Montana, showing that this lineage spanned much of western North America. Pachycephalosaurs like Sphaerotholus were bipedal plant-eaters that fed on low vegetation, fruits, and possibly insects. Palaeontologists suggest their reinforced skulls were used in flank-butting, head-shoving, or visual displays during social interactions.

It possessed a distinct row of bony nodes that formed a continuous horizontal bar around the back of its skull dome.

Where and when

Sphaerotholus lived in the Late Cretaceous, from 73 to 66 million years ago (Campanian-Maastrichtian age). Its remains come from United States, in the Kirtland Formation.

The numbers

Length 2.2 m (estimates run from 1.8 to 2.5 m). Mass about 35 kg. Hip height about 0.8 m. That is 1.3 human-lengths, or 0.2 of a double-decker bus. These are estimates from partial skeleton; fields marked estimated by the site are length, mass, hip height.

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