Hairy Museum of Natural History

The holotype skeleton of Yinlong downsi.
Photo Credit: IVPP

Meet Yinlong downsi, the earliest ceratopsian yet discovered. The name Yinlong means “Hidden Dragon,” due to the fact that the fossil was found in China where the movie “Crouching Tiger, Hidden Dragon” was filmed, while “downsi” honors the life and work of Will Downs.

Yinlong comes from early Late Jurassic rocks, 20 million years earlier than the next-oldest ceratopsian and a good 80 million years before well-known ceratopsians like Triceratops. As might be expected, Yinlong seems to come from the base of the ceratopsian family tree, and its relatively unspecialized nature is helping scientists figure out exactly what other dinosaurs ceratopsians are related to.

For about 20 years, paleontologists have suspected that the horned and frilled ceratopsians were closely related to the thick-headed pachycephalosaurs. This relationship was largely based on the fact that both groups had a shelf of bone that extended back over the base of the skull, a feature that has led scientists to combine the two into one overarching group–the Marginocephalia (“Shelf-heads”). But the skulls of both these groups are so highly modified that there has been some debate as to whether this was an actual feature that they inherited from a common ancestor, or just an accidental similarity that each group independently developed while evolution was messing with their heads.

The skull of Yinlong downsi (snout is to the left).
Photo Credit: James M. Clark

The anatomy of Yinlong points to the former scenario. The beak-like rostral bone at the tip of its snout is a defining feature of the Ceratopsia and places Yinlong squarely in that group. But the expansion of the back of its skull is more similar to pachycephalosaurs than ceratopsians, complete with roughened borders and small knobs of bone. Yinlong seems to show that both ceratopsians and pachycephalosaurs started out with a similar expansion of the back of their heads before evolving their own distinct extravagances–ceratopsians with long horns and shield-like frills, and pachycephalosaurs with nodes, knobs, spikes, and domes.

As if that weren’t enough, Yinlong offers clues to the origin of the Marginocephalia as well. Yinlong seems to bridge the gap between advanced marginocephalians and an earlier group of dinosaurs, the heterodontosaurs. This relationship has been suggested before, but Yinlong seems to offer the best evidence to date, with several characters of its skull and postcranial skeleton shared with the Heterodontosaur family.

Xu X., Forster, C. A., Clark, J. M., & Mo, J. 2006 “A basal ceratopsian with transitional features from the Late Jurassic of northwestern China.” Proceedings of the Royal Society B: Biological Sciences. First Cite Early Online Publishing.

George Washington University has a press release online in addition to the images shown here. A PDF of the paper is available to download as well. All this brought to my attention via the good folks on the Dinosaur Mailing List, a great way to keep up on the latest Mesozoic news.

—Matt Celeskey.

File under: Dinosaurs, Jurassic, Recent Discoveries.