Tyrannosauroid integument reveals conflicting patterns of gigantism and feather evolution

Abstract

Recent evidence for feathers in theropods has led to speculations that the largest tyrannosaurids, including <i>Tyrannosaurus rex</i>, were extensively feathered. We describe fossil integument from <i>Tyrannosaurus</i> and other tyrannosaurids (<i>Albertosaurus, Daspletosaurus, Gorgosaurus</i> and <i>Tarbosaurus</i>), confirming that these large-bodied forms possessed scaly, reptilian-like skin. Body size evolution in tyrannosauroids reveals two independent occurrences of gigantism; specifically, the large sizes in <i>Yutyrannus</i> and tyrannosaurids were independently derived. These new findings demonstrate that extensive feather coverings observed in some early tyrannosauroids were lost by the Albian, basal to Tyrannosauridae. This loss is unrelated to palaeoclimate but possibly tied to the evolution of gigantism, although other mechanisms exist.