Giant Yutyrannus huali Had 56 Teeth, Feathers

Friday, September 28, 2018

A restoration of Yutyrannus huali

At Wauconda Library's summer STEAM camp, a young patron wanted to know, "How many teeth do Yutyrannus have?"

It's hard to imagine what a 30-foot-long, 1½-ton dinosaur would do with feathers. Take flight? Impossible. Discovered six years ago in northeastern China, the Yutyrannus huali, an early T. rex cousin, is the largest dinosaur discovered so far that features plumage.

This feather-accessorized dino came along about 125 million years ago, 60 million years before T. rex. Yutyrannus stood upright on two legs. Its arms were longish, each with three fingers, topped by a yardstick-long head. The Yutyrannus had an oversized mouth full of teeth.

Corwin Sullivan, associate professor, and Philip J. Currie, professor of Vertebrate Paleontology at Canada's University of Alberta, studied the Yutyrannus huali fossils.

When asked how many teeth were in Yutyrannus' gigantic mouth, Sullivan said, "My guess would be about 56 in total." By comparison, its five-times larger, featherless T. rex cousin crushed prey using about 60 choppers.

The fossilized remains of three Yutyrannus -- one adult and two youth -- were found in slate slabs. It takes the trained eye of a paleontologist to decode the markings that indicate the presence of feathers.

"The feathers are preserved as dark linear streaks on the slabs containing the fossils," Corwin said. "In life, the feathers would have resembled bristles or hairs, rather than the blade-like feathers of modern birds. Their function was almost certainly insulation and/or visual display, rather than anything to do with flight."

A simplified cladogram showing the systematic position of Y. huali among the Tyrannosauroidea.  Xu, X., Wang, K., Zhang, K., Ma, Q., Xing, L., Sullivan, C., Hu, D., Cheng, S., and Wang, S. 2012. A gigantic feathered dinosaur from the Lower Cretaceous of China.

The area in China where Yutyrannus was uncovered is rich in fossilized dinosaur remains, including the very first discovery of a feathery dino, a much smaller dinosaur species called Sinosauropteryx.

The quarry and surrounding area has yielded a bumper crop of animal and plant fossils representing both the Jurassic and Cretaceous periods, which ranges from amphibians, plants, fish, mammals and winged pterosaurs to ancient birds. Ten dinosaur museums near the quarry feature the many incredible dinosaur fossils.

Corwin said dinosaurs like Yutyrannus were globally widespread, though not necessarily present on every continent.

Speculating as to why the giant might have needed feathers, Corwin said, "Although most of the Cretaceous was characterized by a warm climate, northeast China seems to have been relatively cool during the specific time when Yutyrannus existed, approaching modern conditions. The cooler temperatures may at least partly explain the occurrence of feathers, which could have had an insulating function."

Another feathered dinosaur, Caudipteryx, a peacock-sized creature, emerged about 5 million years before Yutyrannus and has captured Corwin's attention.

"Caudipteryx represents an early and preliminary step down an intriguing evolutionary pathway, and is also among the most primitive dinosaurs to possess feathers of the pennaceous (blade-like) type seen in modern birds."