This nearly complete skeleton belongs to a juvenile of a newly identified species named Zavacephale rinpoche, dating back about 108 million years to the Early Cretaceous Period. Zavacephale rinpoche is the oldest and most complete pachycephalosaur fossil found to date, predating others by approximately 15 million years. Measuring about one metre long and weighing just under six kilograms, this teenage dinosaur had a well-developed cranial dome formed mostly by a single skull bone, unlike later pachycephalosaurs whose domes are formed by two bones. Small spikes and nodes decorated the dome and the back of its skull. Researchers determined the dinosaur's age through growth rings in its limb bones-similar to tree rings-to reveal when the dome fully developed. The function of the dome is still uncertain, but scientists suggest it may have been used for head-butting to establish dominance, similar to modern-day bighorn sheep. The discovery of Zavacephale adds crucial knowledge about this little-understood dinosaur group, offering new insights into their anatomy, evolution, and behaviour. "The consensus is that these dinosaurs used the dome for socio-sexual behaviors. The domes wouldn't have helped against predators or for temperature regulation, so they were most likely for showing off and competing for mates," said paleontologist Lindsay Zanno of North Carolina State University and the North Carolina Museum of Natural Sciences, senior author of the study published on Wednesday in the . "Were they for head-butting, grappling or just showing off?" Zanno asked. "At the end of the day, you have to hand it to pachycephalosaurs. When it comes to flashy headgear, they didn't phone it in." Artist impression shows two individuals of the newly identified Cretaceous Period dinosaur species Zavacephale rinpoche butting heads. Photo Credit: Reuters A completely formed dome on a juvenile indicates that pachycephalosaurs engaged in social and likely mating behaviors before becoming fully grown, Zanno said. Adults of the largest pachycephalosaurs, like the later Pachycephalosaurus from North America, could grow to around 14 feet long (4.3 meters), though adults of Zavacephale may have been less than half of that length. The environment in which Zavacephale lived was a valley dotted with lakes and surrounded by cliffs. The remains of multiple other plant-eating dinosaurs have been found nearby as well as various fish, turtles and croc relatives. The name Zavacephale combines the Tibetan word for "origin" with the Latin word for "head," owing to the fact that this species is the earliest-known example of dome-headed dinosaurs. "Before Zavacephale, our record of pachycephalosaurs was almost exclusively limited to their indestructible domes. With such scanty skeletons, we were left with holes in our knowledge of their anatomy, including basic things like what their arms would have looked like, how their digestive system functioned and how the cranial dome evolved over time," Zanno said. The fossil preserved gastroliths, the stomach stones that helped the dinosaur grind the plants it ate. Scientists are trying to figure out the evolutionary ancestry of pachycephalosaurs. "We've been missing transitional forms that can shed light on how their bizarre cranial domes evolved and resolve their relationships to other dinosaurs," Zanno said.