Yutyrannus

Phylogeny: Dinosauria > Saurischia > Theropoda > Neotheropoda > Tetanurae > Avetheropoda > Coelurosauria > Tyrannosauroidea > Proceratosauridae (?)

Overview: By the mid-1990’s, most paleontologists accepted that Tyrannosaurus and its relatives were coelurosaurian theropods, not carnosaurs. This made them closer to modern birds than they were to theropods like Allosaurus. Considering they belonged to the same lineage that would give rise to birds, some speculated that at least some tyrannosaurs would’ve possessed proto-feathers in life, at least in the case of smaller genera. In 2012, paleontologists in China would formally name and describe a genus that proved even some larger tyrannosaurs were feathered. This genus, called Yutyrannus, was found within the rocks of the Yixian Formation, in China’s northeast. Its name was derived from both Mandarin Chinese and Greek, meaning “feathered tyrant”, referring its status as a tyrannosaur and to its fluffy integument. Said integument took the form of fur-like and relatively simple feathers that covered most of its body, preserved in the rock matrix surrounding the rather well preserved holotype specimen. Remarkably well preserved specimens of feathered dinosaurs are common in the Yixian Formation, thanks to its fine volcanic sediments.

The earliest ancestors of the tyrannosaurs, like Proceratosaurus and Guanlong, were quite small, being about two to four meters long, with lightly built bodies. Yutyrannus, which lived during the Early Cretaceous, is notable for its size in combination with its proto-feathers, being the largest of any dinosaur genus yet found with evidence of such integument. Adults are estimated to have been up to seven to nine meters long. What’s interesting is that Yutyrannus was a basal tyrannosaur and is often classified within the family Proceratosauridae, alongside Guanlong. Yutyrannus is not only proof that some tyrannosaurs were feathered, it also reveals that large body sizes evolved early on and independently from the later tyrannosaurids. Yutyrannus had some rather basal traits, such as its relatively long arms and three clawed digits, as well as low crests running along its snout. It was likely the top predator of the Yixian environment. The climate in the region was relatively mild, so having proto-feathers provided extra insulation during cooler months. Some of its later relatives, like Tyrannosaurus itself, had limited integument or possibly lost it as they grew even larger.