A new species of feathered dinosaur has been discovered, and its gigantic size makes it the largest-known feathered animal, living or extinct.

Yutyrannus huali lived in northeastern China 125 million years ago, according to a group of scientists in China, where three specimens of the bipedal tyrannosaur were found. A description of the new dinosaur is published in the March 5 issue of Nature. (Scientific American is part of Nature Publishing Group.)

Only a meter shorter than Tyrannosaurus rex, Yutyrannus weighed at least 1,400 kilograms and was nine meters long, or almost the length of a school bus, with filamentous plumage at least on its neck, pelvis and legs. The researchers think that the feathers, which in some cases were as long as a brand new No. 2 pencil, covered Yutyrannus’s entire body.

Before now, Beipiaosaurus was the largest-known non-avian feathered dinosaur, and it was a huggable turkey-sized mass just two meters or so long. Scientists never expected to find plumage on a dinosaur as large as Yutyrannus, because, at least in mammals, larger-sized animals retain heat more efficiently than small animals. That puts larger animals at higher risk of overheating in warm weather, so insulative features such as feathers or fur are often lost in large mammals.

Yet Yutyrannus demonstrates that the loss of plumage is not necessarily a consequence of large size in dinosaurs. Xing Xu, a paleontologist at the Chinese Academy of Sciences's Institute for Vertebrate Paleontology and Paleoanthropology, who led the study, said that Yutyrannus may be unique among gigantic dinosaurs because it lived in a climate that was cooler by eight degrees Celsius than other dinosaur habitats at that time—perhaps Yutyrannus needed the feathers to keep warm.

There is another possible explanation. Some gigantic maniraptoran dinosaurs (or “raptors,” a sister group to tyrannosaurs which includes extant bird species) are assumed to have possessed feathers, but direct evidence of plumage has never been found. If paleontologists find additional gigantic dinosaurs with feathers, it may be that dinosaurs are not governed by the same thermodynamic rules as mammals. That would certainly ruffle some feathers.