Photo/Illutration An artist's rendering depicts two domed pachycephalosaurs engaged in head-butting behavior. (Provided by the Fukushima Museum, © Masato Hattori)

A research team said it has discovered the oldest known pachycephalosaur, the so-called head-butting group of dinosaurs distinguished by their thick, dome-shaped skulls.

The researchers from the Okayama University of Science, the Fukushima Museum and other institutes said the fossilized remains of the specimen were found in a Lower Cretaceous (about 110 million years ago) rock layer in Mongolia’s Gobi Desert.

They described it as a new genus and species of pachycephalosaur.

The findings were published in the British scientific journal Nature on Sept. 17.

Most pachycephalosaur fossils are from layers dating to the end of the Mesozoic Era (about 80 million to 66 million years ago). No fossils from an earlier period had been known.

In 2019, the research team unearthed a complete skeleton of this dinosaur in the Gobi Desert, and an analysis revealed it to be one of the earliest diverging, or most primitive, pachycephalosaur species.

It is also the world’s first discovery of a pachycephalosaur with its hand bones and a complete tail preserved, the researchers said.

The dinosaur was estimated to be 1 meter long and weighing 5.85 kilograms. Growth lines on its leg bones indicate it was a young individual only 2 or 3 years old.

A dome-shaped skull was also confirmed.

While it has been theorized that the dome was used for social or sexual displays, the fossil shows the feature developed before the animal reached full physical maturity.

Researchers suggest this could mean that even in their early evolutionary stages, pachycephalosaurs may have engaged in contests for mates.

However, they said there is still no direct evidence that pachycephalosaurs actually butted heads.

The team gave the dinosaur the scientific name Zavacephale Rinpoche by combining three words: “zava,” a Tibetan word for “root” or “origin”; “cephale,” Latin for “head”; and “rinpoche,” a Tibetan word meaning “precious one.”

The full name translates to “primitive precious head.”

Pachycephalosaurs are popular among fans due to their unique appearance and character. They have been featured in the “Jurassic Park” movie series and video games.

The researchers say their discovery will not only help them investigate the purpose of the dome but also allow them to study the dinosaur’s diet by analyzing its teeth.

“I believe this will allow us to get much closer to understanding the social behavior of dinosaurs, which were different from those of modern reptiles,” said Junki Yoshida, a curator at the Fukushima Museum in Aizu-Wakamatsu, Fukushima Prefecture.

A replica of the complete skeleton will be on display from Sept. 18 to Oct. 19 at the Museum of Dinosaur Research at Okayama University of Science in the capital of Okayama Prefecture, as well as at the Fukushima Museum.

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