It has yet to be determined why such an integumentary change might have occurred. A precedent for feather loss can be seen in other dinosaur groups such as ornithischians, in which filamentous structures were lost, and scales reappeared. Although gigantism has been suggested as a mechanism, Phil R. Bell, who co-authored the study, noted that the feathered "Yutyrannus" overlapped in size with "Gorgosaurus" and "Albertosaurus". "The problem here is that we have big tyrannosaurs, some with feathers, some without that live in pretty similar climates. So what's the reason for this difference? We really don't know.”