Fortuitously, I have a couple of biology posts lined up today. The first one, which comes Via Ed Yong, describes a huge new species of dinosaur that was covered with feathers. A new paper in Nature by Xu et al. describes the discovery in China of three nearly complete skeletons of Yutyrannus huali, a very large theropod dinosaur that was covered with filamentous feathers. (“Yu” is Mandarin Chinese for “feathers,” “tyrannus” is Latin for “king,” and “huali” means “beautiful” in Mandarin.) The species is related to T. rex, also a theropod.
The beautiful feathered king was found in Liaoning Province, China, and here’s a slab preserving two of the specimens. The line drawing tells you what you’re seeing. These were very large individuals: the giggest weighed about 1414 kg, and the smaller ones, probably juveniles, about 600 and 400 kg respectively. Those are big dinos: 1414 kg is 3,117 pounds, exactly the weight of a 1990 Volvo GLE.
According to the authors, the dino’s most striking feature is its “highly pneumatic midline crest resembling that of Guanlong and the carcharadontosaurian Concavenator. . “. Here’s a reconstruction of the smaller Guanlong‘s cranial crest from Dinopedia (the beast was about 3 m long). We don’t know what these crests were for: the color below implies one hypothesis, which was display. In other dinosaurs they might have been used to exaggerate sound production, but I’m not sure whether they’re hollow in Y. huali.
Below is Figure 2 from the new paper, showing the skull and mandible of Y. huali. The crest is visible at the top of the skull, but it’s not as elaborate as that of Guanlong (see the reconstruction below).
The important feature here are the filamentous “feathers” that you can see in sections c-h of the photographs (click to enlarge):
According to the authors, the feathers (described as “filamentous integumentary structures,” are seen in all three specimens, are very long (15 cm, about 6 inches), and are found on the back and neck, on the forearms, and near the pelvis. This implies that the whole damn beast was covered with filamentous feathers, and that’s seen in this artistic reconstruction from Ed Yong’s site:
What were the feathers for? Certainly not for flight, since these things are too big to either jump in the air (“ground up” theory) or glide down from trees (“trees down” theory), and at any rate the feathers are too thin to provide any lift. The authors suppose that they might represent “an adaptation to an unusually cold environment,” since the species lived during a period of weather that was unusually cold during the Cretaecous. And although dinos were supposedly “cold blooded” (ectothermic), there’s some evidence that they were really “warm-blooded”; this is based on morphological evidence and the fact that these dinos might have been fast-moving rather than sluggish, which would require a high metabolism.
A reasonable theory, then, is that many theropod dinosaurs developed feathers for insulation, and these were later co-opted for flight. This is supported by the finding of this new large beast with rudimentary feathers. (An alternative theory is that they were used for sexual or species-specific displays.) Since feathers supposedly evolved only once (I can’t disgorge the evidence for this, but that’s my recollection), then their use in flight would represent what Steve Gould called an “exaptation”: the evolution of a new function for a trait that originally evolved for a different one (penguins’ use of their flippers for underwater “flying” is another example).
Here’s where Yutryannus fits into the phylogenetic tree of tyrannosaurs. The ones known to be feathered are shown as feathered, but it’s also possible that even T. rex itself was, as I suggested in WEIT, covered with fluff. That would detract a bit from its fearsome reputation!
Xu, X., K. Wang, K. Zhang, Q. Ma, X. Xing, C. Sullivan, D. Hu, S. Cheng, and S. Want. 2012. A gigantic feathered dinosaur from the Lower Creataeous of China. Nature online: doi:10.1038/nature10906