A ten-metre tyrannosaur relative wore feathers twenty centimetres long
Yutyrannus, a cousin of Tyrannosaurus from early Cretaceous China, is the largest dinosaur known with direct fossil evidence of feathers. Its adult was perhaps 10 metres long and roughly 1.4 tonnes, around forty times heavier than the previous record holder, and its body carried long, hair-like filaments.
Xu Xing and colleagues named the animal in 2012. The genus name blends the Mandarin word for feather with the Greek for tyrant, and the species name huali means beautiful, a nod to its plumage. Three nearly complete skeletons, an adult, a subadult and a juvenile, came through a fossil dealer who said they were all dug from one quarry at Batu Yingzi in Liaoning Province. That points to the Yixian Formation, about 125 million years old. The dealer had sawn the slabs into bath-mat-sized pieces that two people could carry.
Size estimates vary. The describers put the adult at 10 metres and about 1,414 kilograms, while Gregory S. Paul in 2016 suggested a smaller 7.5 metres and 1.1 tonnes. The adult's skull was about 90.5 centimetres long, and its snout bore a tall central crest flanked by wavy ridges that were probably for display. Compared with later tyrannosaurs it kept primitive features such as long three-fingered arms and a short foot not built for running.
Feather imprints appear on the hips, feet, tail, neck and upper arm, reaching up to 20 centimetres. Preservation was too poor to say whether the filaments were simple or branched. If they covered the whole body, they may have kept the animal warm in a region averaging around 10 degrees Celsius a year; if they were patchy, display is another option. An early suggestion that the filaments were merely feather precursors is now considered overturned.
The find reopened the question of whether giant later tyrannosaurids were feathered too. Scaly skin impressions from Tyrannosaurus, Tarbosaurus and Gorgosaurus come from body areas where Yutyrannus had feathers, and no positive evidence of plumage in those giants exists. Some researchers propose that they evolved scales again, perhaps as bodies grew larger or climates warmed, so body covering may have changed over tyrannosaur history.
Source: Yutyrannus
