A new dome-skulled dinosaur from Mongolia sheds light on the early history of one of the most poorly known dinosaur groups of all.
Discovered in Khuren Dukh in the Eastern Gobi Desert, Mongolia, the new dinosaur has been published in Nature by Tsogtbaatar Chinzorig of the Mongolian Academy of Sciences in Ulaanbaatar and a team of colleagues.
It’s one of the most complete members of its group – the pachycephalosaurs or dome-skulled dinosaurs – ever discovered, only lacking the neck, much of the ribcage and part of the lower arm and hand. Its skull is exquisitely preserved.
Tsogtbaatar and colleagues have named it Zavacephale rinpoche, this combining the Tibetan for ‘root’ or ‘origin’ with the Latin for ‘head’. The species name means ‘precious one’ in Tibetan. This partly refers to the discovery of the skull “exposed on a cliff like a cabochon jewel”. It was small, less than 1m long and less than 10kg.
Pachycephalosaurs are omnivorous or herbivorous, bipedal dinosaurs, famous for their thickened skull roofs. They’re cousins of ceratopsians, the horned dinosaur group that includes Triceratops.
Several competing views exist on pachycephalosaur evolution and one is that they only evolved domed skulls late in their history. Zavacephale contradicts this. Dating to between 115 and 108 million years ago and thus to the Early Cretaceous, it’s one of the oldest members of the group, yet is fully domed. The majority of pachycephalosaurs are from the Late Cretaceous and 80-66 million years old.
Furthermore, the only known Zavacephale specimen is not fully grown, showing that the dome was present before the animal reached full size. This matches a pattern widespread in non-bird dinosaurs: they developed features relating to display or combat during their teen years, before growth had ceased.
Zavacephale contradicts another idea about pachycephalosaurs: that the skull was flat throughout teenage life and that the dome only developed in adulthood.
Another surprise is that the specimen contains gastroliths, or stomach stones, the sharp edges of which suggest an omnivorous diet. This could show gastroliths were widespread across dinosaurian omnivores as well as herbivores. Omnivorous habits are also consistent with the animal’s fang-like front teeth. Its long, slender hindlimb bones suggest speedy running abilities.
Researchers have hoped for decades that better pachycephalosaur remains might one day provide more information on their details, and they remain an extremely rare group of dinosaurs.
Top image: Zavacephale rinpoche skull. Credit: Tsogtbaatar Chinzorig
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