A recent discovery in Mongolia’s Gobi Desert has provided the most complete and oldest fossil of an iconic dome-headed dinosaur to date.
This new species, named Zavacephale rinpoche, lived about 108 million years ago (Early Cretaceous period).
Palaeontologists from North Carolina State University announced the findings on September 17, describing it as a “once-in-a-lifetime discovery.”
It belongs to the group pachycephalosaurs — dinosaurs known for their unique head adornments, including domes of thickened bone, horns, and bony knobs.
Mostly, the fossils are rare and often just fragmentary pieces of skulls.
Interestingly, the new fossil belongs to a juvenile dinosaur, but it already had a fully formed head dome.
“It is remarkable for being the oldest definitive pachycephalosaur, pushing back the fossil record of this group by at least 15 million years, but also because of how complete and well-preserved it is,” said Lindsay Zanno, head of paleontology at the North Carolina Museum of Natural Sciences.
Small, plant-eating dinosaur
The well-preserved fossilized remains were unearthed in the Khuren Dukh locality of the Eastern Gobi Basin of Mongolia.
Roughly 108 million years ago, the region was a lakeside valley nestled among cliffs and steep slopes.
Pachycephalosaurs were plant-eating dinosaurs. The adults could reach up to 14 feet long (4.3 meters) and seven feet tall (2.1 meters), with an approximate weight of 800 to 900 pounds (363 – 410 kilograms).
“It was a small animal – about three feet or less than one meter long – and the most skeletally complete specimen yet found,” said Tsogtbaatar Chinzorig, the lead author from the Mongolian Academy of Sciences.
The dinosaur group is often depicted engaging in headbutting contests.
According to Zanno, the species used their large head domes for socio-sexual behaviors, such as showing off and competing for mates.
The domes were likely not useful for defending against predators or regulating body temperature.
“If you need to headbutt yourself into a relationship, it’s a good idea to start rehearsing early,” Zanno said in the press statement.
Fossilized stomach stones
The specimen offers an “unprecedented glimpse” into the anatomy of these dinosaurs.
For instance, the fossilized stomach stones (gastroliths) were used by this dinosaur to grind food.
“The newly recovered materials of Z. rinpoche, such as the hand elements, the stomach stones (gastroliths), and an articulated tail with covered tendons, reshape our understanding of the paleobiology, locomotion, and body plan of these ‘mysterious’ dinosaurs,” added Chinzorig, who discovered the fossil.
Furthermore, the fossil discovery is important for understanding how the cranial domes grew.
The fragmentary bones made it tough to figure out if different-looking skulls belonged to different species or just to dinosaurs at various stages of growth.
The juvenile fossil with a fully formed dome provides a link between a dinosaur’s age and its cranial development.
The findings also suggest that the domes of pachycephalosaurs grew faster than the rest of their bodies.
Unlike later pachycephalosaurs, whose domes integrated more of the skull, this specimen’s dome was found to consist mainly of the forehead bones.
Its name comes from a combination of Tibetan and Latin words that mean “precious root head,” referencing its discovery as a valuable, “jewel-like” skull.
The Zavacephale rinpoche fossil has filled major gaps in the pachycephalosaur timeline, providing new information on both their evolutionary history and growth.
The findings were reported in the journal Nature.