Two New 'Iconic and Bizarre' Dinosaur Species Discovered

Two new species of an "iconic and bizarre" dinosaur group have been discovered in North America.

Researchers found the pair of species—described in a study published in the journal Papers in Palaeontology—in eastern Montana and southern Alberta, Canada, respectively.

They lived in the last part of the Cretaceous period (around 145 million years ago to 66 million years ago), just before the mass extinction event that wiped out the majority of plant and animal species on Earth, including all non-avian dinosaurs. The event, which occurred around 66 million years ago, is thought to have resulted from a giant asteroid impact.

The species belong to a group of dinosaurs known as the pachycephalosaurs, which are characterized by a unique feature on their heads.

"Pachycephalosaurs are the 'dome-headed' dinosaurs. They walked around on two legs and ate plants, but what makes them so iconic and bizarre is that most of them had a large spherical mass of solid bone on the top of their heads," Cary Woodruff, a paleontologist with the Phillip & Patricia Frost Museum of Science and author of the study, told Newsweek.

"The largest member of this group was called Pachycephalosaurus, and it could have a dome around 9 inches thick!"

Pachycephalosaur behavior, including the function of the domed heads, is the topic of much scientific research and debate.

"Some paleontologists think they used their domed heads to butt heads like bighorn sheep. Others think this elaborate headgear was for telling species apart," Woodruff said.

"And the domes developed as the animal grew up—young ones had a flat to small dome, and it grew larger and larger as the animal got older—so some think it was like a visual billboard to show off things like species identification, age, and maybe even gender."

Woodruff and colleagues described the two new species based on a single skull bone, called the squamosal, in both cases. The researchers have named the species found in Montana Sphaerotholus triregnum, while the one uncovered in Alberta has been dubbed Sphaerotholus lyonsi.

Both would likely have measured around 6 feet long from nose to tail, according to Woodruff. And the dome on the top of their heads would have been about the size of an orange.

The newly uncovered dinosaurs belong to the dog-sized pachycephalosaur genus (group of species) Sphaerotholus, and the latest findings shed new light on these creatures.

"While most pachycephalosaurs had a large, spherical dome, the skull bones around the dome were incredibly diverse—some had big spikes coming off these peripheral bones, others had rows of little bumps and lumps, others spikes and bumps," Woodruff said. "These bones that ringed the dome are the main bones we use to recognize and identify each species of pachycephalosaur.

"Previously, paleontologists had discovered three other species of Sphaerotholus, and what made them unique was that they had small pointy bumps called nodes in a single row that went around the dome. But S. triregnum and S. lyonsi had multiple node rows. S. triregnum had three rows and S. lyonsi had two rows."

S. triregnum and S. lyonsi lived 66 million years ago and 77 million years ago, respectively. The environments they inhabited would have looked very different from how they are today. Back then, both areas would have been warm, humid, and lush environments.

Living alongside these two dinosaurs in the same period were the previously mentioned Sphaerotholus species that had single rows of nodes around the head domes.

This suggests that throughout the end of the Cretaceous, there were two lineages of Sphaerotholus—one with a single row of nodes on their head and another with multiple rows—living together.

"We don't know what explains these two lineages—for example, was it so they could tell one another apart? But we can see that not only did these lineages live alongside one another, but they were also evolving alongside one another right up to the mass extinction that ended the reign of the non-avian dinosaurs 66 million years ago," Woodruff said.

S. triregnum and S. lyonsi are from the Hell Creek Formation and the Dinosaur Park Formation, respectively. These are two of the most extensively studied dinosaur-bearing geological formations on Earth. Yet, this is the very first time that either of the species had been found, which suggests they may still be hiding more unknown smaller dinosaurs.

"These formations are famous for big dinosaurs like Triceratops and Tyrannosaurus. It's a lot easier to find big dinosaur bones eroding out of hill," Woodruff said. "And previous studies had hypothesized that while we may have found most of the big dinosaurs from such famous formations, we're likely to continue to find new small species."