Sphaerotholus

Sphaerotholus is a genus of pachycephalosaurid dinosaur that lived during the Upper Cretaceous period in what is now the western United States and Canada. These dinosaurs are known for having thick, domed skulls, which may have been used in head-butting battles or displays among members of the same species.

Scientists have identified five different species of Sphaerotholus. The first one discovered was S. goodwini, found in rocks from the Den-na-zin Member of the Kirtland Formation and possibly the Fossil Forest Member of the Fruitland Formation in San Juan County, New Mexico, USA. Other species include S. buchholtzae from the Hell Creek Formation in Montana, USA, and the Frenchman Formation in Saskatchewan, Canada; S. edmontonensis from the Horseshoe Canyon Formation in Alberta, Canada; S. lyonsi from the Dinosaur Park Formation in Alberta, Canada; and S. triregnum from the Hell Creek Formation in Garfield County, Montana, USA.

These discoveries help scientists understand more about the diversity and behavior of pachycephalosaurids. By studying their fossils, researchers can learn about how these dinosaurs lived, moved, and interacted with each other millions of years ago.

History of discovery

The name Sphaerotholus comes from Greek words meaning "ball" and "dome", referring to the special dome-shaped skull of this dinosaur. This dinosaur lived from New Mexico to Montana for about 7 to 8 million years during the time of the dinosaurs. Scientists first described Sphaerotholus in 2002 and say it is a highly advanced type of pachycephalosaur.

Species

Sphaerotholus goodwini

This dinosaur species is known from an incomplete skull found in New Mexico. It was named to honor paleontologist Mark Goodwin. Some scientists think another dinosaur called Stegoceras novomexicanum might be a younger version of this species.

Sphaerotholus edmontonensis

Originally described in 1943, this species was later renamed Sphaerotholus edmontonensis in 2010. It had special bony bumps on the back of its skull and grew to about 2 meters long and weighed around 40 kilograms.

Sphaerotholus buchholtzae

The holotype of this species is an incomplete skull from the Hell Creek Formation. It was named for Emily A. Buchholtz. Some scientists thought it was the same as another species, but later studies showed they are different.

Sphaerotholus lyonsi

This species was described in 2023 and lived in Canada about 76 million years ago. It had two rows of small bony bumps on the back of its skull.

Sphaerotholus triregnum

Also described in 2023, this species lived in Montana. It had three rows of small bony bumps on the back of its skull, giving it a crown-like appearance.

Classification

In 2023, scientists studied two species of Sphaerotholus, named S. lyonsi and S. triregnum. They looked at where this dinosaur fits in the family of pachycephalosaurids. They found that all the suggested species of Sphaerotholus belong together in a special group. This group is closely related to another group of pachycephalosaurids called Pachycephalosaurini. You can see their results in the family tree shown below.