Recent years have seen the discovery of large numbers of feathered non-avian Theropod Dinosaurs, though most of these have been small in size. The 5 April edition of the journal Nature contains a paper by a team of scientists led by Xing Xu of the Institute of Vertebrate Paleontology and Paleoanthropology at the Key Laboratory of Evolutionary Systematics of Vertebrates at the Chinese Academy of Sciences, describing for the first time the discovery of feathers on a much larger Dinosaur.
The new Dinosaur, which has been named Yutyrannus huali ('beautiful feathered tyrant') is a Tyranosaurid from the Lower Cretaceous Yixian Formation of Liaoning Province, roughly 125 million years old, and is thought to have weighed up to 1.4 tonnes and to have reached 9 m in length; not the largest of Tyranosaurids, but much bigger than any feathered dinosaur discovered to date.
Reconstruction of Yutyrannus huali in life. The smaller dinosaurs to the left are Beipiaosaurus. Brian Choo/Chinese Academy of Sciences.
Yutyrannus huali is described from three specimens, an adult and two juveniles. Each of the specimens had feathers preserved on a different part of the body; the tail on the adult, a foot on one of the juveniles, the neck and upper fore-limb of the other. From this the researchers conclude that the living animals had feathers over much of their bodies.
The feathers were simple filaments, closer to the down of chicks than the feathers of an adult bird.
To date feathers have been found in only quite small dinosaurs and have been explained in three different ways; they could be used for flight (or at least gliding to some extent, a possibility for many small dinosaurs), they could be used as insulation, or they could be used for communication. Yutyrannus is clearly to large to have got airborne in even the most rudimentary attempt at flying. On the current data it is impossible to say if the feathers of Yutyrannus could have been used for communication. Recently there have been a number of breakthroughs in determining the colour of preserved feathers, so this is a possible avenue for future research. Larger Dinosaurs have generally been considered to have achieved thermal inertia by their size; able to maintain heat through their shear bulk (small animals have a large surface area compared to their mass, and consequently have difficulty maintaining their body temperature, for bigger animals the ratio decreases, and loosing heat can become a problem).
The temperature at Yixian is thought to have averaged 10°C over the course of the year. This is equivalent to a cool-temperate climate today, such as that of northern China, but would have been exceptionally cool for the Mesozoic, particularly as the temperature can be presumed to have fallen beneath this average for part of the year. This make the possibility that insulation was needed on Yutyrannus more than on other large Theropods. There is also the possibility that other large Theropods were also feathered, but that we have yet to discover evidence of this.
The skull (top) and part of the tail of Yutyrannus huali (bottom). Filaments are visible on the tail. Zang Hailong/Chinese Academy of Sciences.
See also The bite of T. rex, A review of Jurassic Tyrannosauriods leads to the description of a new genus, Was Archaeopteryx black? How did raptors use their claws? (and did it help them learn to fly?) and Dinosaurs on Sciency Thoughts YouTube.
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