Sphaerotholus | “Dome Head” Dinosaur from the Late Cretaceous

Sphaerotholus, whose name means “Ball Dome Head,” belonged to the Pachycephalosauridae family which were known for their distinctive dome-shaped skulls. This dinosaur in particular was an herbivore that lived during the Late Cretaceous period. Its fossilized remains have been found in a number of places in the Western parts of North America. I think the great geographical range, and long time-span it existed is a testament to its evolutionary success.

Sphaerotholus Key Facts

Sphaerotholus Taxonomy and Timeline

The name Sphaerotholus is derived from the Greek words ‘sphaira’ meaning ‘ball’ and ‘tholos’ meaning ‘dome’. An apt name for a dinosaur with an espcially large dome-shaped head for its size. It belongs to the Pachycephalosauridse family, known for their distinctive dome-shaped skulls.

The type species of this genus is Sphaerotholus goodwini. Named in honor of paleontologist Mark Goodwin for his significant contributions to the study of pachycephalosaurid dinosaurs. After the first description of S. goodwini, no less than four more species of Sphaerotholus have been described.

Several different species of Sphaerotholus lived during the Late Cretaceous period, specifically from the Late Campanioan to the Late Maastrichtian epoch, around 83.5 to 66 million years ago. This was a time when dinosaurs were the dominant terrestrial vertebrates and the earth was warm and teeming with life.

Species of Sphaerotholus

1. S. goodwini, the holotype first described in 2003.
2. S. edmontonensis, first described in 1943 as a Troodon, it was recognized as belonging to Sphaerotholus in 2010.
3. S. buchholtzae, first described in 2003.
4. S. lyonsi, first described as recently as in 2023.
5. S. triregnum, also described in 2024. Named after its characteristical triple rows of small nodes at the back of its skull.

Discovery & Fossil Evidence

Sphaerotholus goodwini was discovered in 2002 by Williamson and Carr in the Kirtland Formation in the San Juan Basin in New Mexico. It was then described in the following year, in 2003 by Williamson and Carr. The holotype, NMMNH P-27403, is an incomplete skull lacking the facial and palatal elements. This discovery was significant as it added a new genus to the Pachycephalosauridae family which would prove to have been wide spread.

Subsequent finds have been made in Alberta and Saskatchewan in Canada as well as in New Mexico and Montana in the USA. These finds have expanded our understanding of the Sphaerotholus’s distribution and provided valuable insights into the dinosaur’s physical characteristics and its environment.

Sphaerotholus Size and Description

With its distinctive dome-shaped head, this dinosaur was a sight to behold. This unique feature is what gives it its name, translating to “Ball Dome Head” from Greek. The dome shape of its skull is a characteristic feature of the Pachycephalosauridae family to which it belongs. It was an herbivore, feeding on the lush vegetation of the Late Cretaceous period. 

Size and Weight of Type Species

There aren’t that many estimations of its size, but from what we have been able to find, there are two estimations by renowned paleontologists to work from. One is the estimation by Gregory S. Paul for the similarly sized S. edmontonensis, at around 6.6 feet length and 80 lbs. Then Thomas Holtz has given a size estimation of around 7.9 feet long and 80-90 lbs weight.

The Dinosaur in Detail

Sphaerotholus is a fascinating dinosaur, not just because of its unique head shape but also due to its characteristics and its place in the Late Cretaceous period. Its dome-shaped skull, a characteristic feature of the Pachycephalosauridae family, is what gives it its name. This unique feature sets it apart from other dinosaurs and is a testament to the diverse forms that dinosaurs took during their reign on earth.

It was an herbivore that fed on the lush vegetation of the Late Cretaceous period. Its diet would have consisted of a variety of plants, including ferns, cycads, and conifers. The shape of its teeth and jaw suggests that it was well adapted to chewing tough plant material. Whether it moved on two or four legs is still a subject of ongoing research.

Sphaerotholus is also notable for its wide distribution and long duration. Fossils of this dinosaur have been found in various locations across Western parts of North America, including New Mexico, Montana, Alberta, and Saskatchewan. This wide distribution suggests that it was a successful species that was able to adapt to different environments and survive over a long period of time.

This was likely a solitary dinosaur although this is still a subject of ongoing research. Its dome-shaped head could have been used for both display and combat. Due to the low number of fossils that have been found, little is known about its senses, such as sight, hearing, and smell. However, like other dinosaurs, it would have relied on these senses for survival, for finding food and avoiding predators. These adaptations made this dinosaur a true survivor of the Late Cretaceous period.

Interesting Points about Sphaerotholus

Contemporary Dinosaurs

Some of its contemporary dinosaurs included Edmontosaurus, Tyrannosaurus, Triceratops, and Ankylosaurus.

Consider Edmontosaurus, a herbivore of considerable size. Its existence alongside Sphaerotholus paints a picture of a landscape abundant in plant life that was capable of sustaining creatures of diverse sizes and appetites. Despite its larger stature, the herbivore Edmontosaurus was not a threat, rather an example of the richness of their shared environment.

Then there was Tyrannosaurus, a predator whose name still evokes awe and fear. Its presence was an obvious potential danger to Sphaerotholus. Yet, the much smaller and nimbler Sphaerotholus may have used its size to its advantage in order to evade the mighty jaws of Tyrannosaurus.

Triceratops and Ankylosaurus were both herbivores like Sphaerotholus that add further depth to this prehistoric scene. The horns and frill of Triceratops and the armored Ankylosaurus present a stark contrast to the much smaller Sphaerotholus. Yet, they all found a way to coexist, each playing their part in the intricate dance of life that unfolded in this bygone era.

List of All Dinosaurs

We have created a list of all dinosaurs we have covered here, sorted across the seven main groups of dinosaurs. We also include information about their type of diet, (omnivore, herbivore or carnivore) and the time they lived.

Frequently Asked Questions

Sources

Article last fact checked:Joey Arboleda, 06-13-2023

Featured Image Credit: ABelov2014, CC BY-SA 3.0, via Wikimedia Commons