Paleontologists have known that small dinosaurs had bird-like feathers, but now three specimens of new tyrannosauroid (T. Rex family) show that at least one much larger dinosaur had a feathery coat as well.

The new species, Yutyrannus huali, means “beautiful feathered tyrant” in a combination of Latin and Mandarin. The three specimens were collected from a single quarry in Cretaceous beds in Liaoning Province, described by both Chinese and Canadian scientists.

Researchers estimate that an adult Yutyrannus would have been about nine metres long and weighing about 1,400 kg, making it tinier than its notorious kin T. Rex, but still 40 times the weight of the largest previously known feathered dinosaur, Beipiaosaurus.

“The feathers of Yutyrannus were simple filaments,” explained Xu Xing, professor at Beijing’s Institute of Vertebrate Paleontology and Paleoanthropology, who led the study.

“They were more like the fuzzy down of a modern baby chick than the stiff plumes of an adult bird,” added Xu, the journal Nature reported.

The large size of Yutyrannus and the downy structure of its feathers would have made flight an impossibility, but the feathers may have had another important function - insulation, said a university statement.

“The idea that primitive feathers could have been for insulation rather than flight has been around for a long time,” said Corwin Sullivan, a Canadian palaeontologist involved in the study.

“However, large-bodied animals typically can retain heat quite easily, and actually have more of a potential problem with overheating. That makes Yutyrannus, which is large and downright shaggy, a bit of a surprise,” said Sullivan.

The explanation may be climate-related, the researchers say. While the Cretaceous Period was generally very warm, Yutyrannus lived during the middle part of the Early Cretaceous, when temperatures are thought to have been somewhat cooler. The gigantic T. rex and its closest kins, conversely, lived in the warm conditions of the Late Cretaceous.

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