“Tyrannosaurus rex and its relatives were North America’s dominant predators in the late Cretaceous period, about 99 million to 65 million years ago, but a new analysis of a toothy fossil skull suggests that the early history of this group includes smaller meat-eating ancestors that date as far back as 170 million years ago. The skull belongs to the only known specimen of Proceratosaurus, which now represents the oldest known relative of T. rex and its cousins, extending the evolutionary history of tyrannosaurs back to the middle of the Jurassic period…Analysis shows a close evolutionary relationship among Proceratosaurus, which was found in England, and other recently described tyrannosauroids found in China, including Guanlong, a 160-million-year-old feathered specimen described in 2006 by Xu Xing of the Chinese Academy of Sciences in Beijing; Dilong, a 130-million-year-old specimen described in 2004 by Xu; and Raptorex, a 125-million-year-old specimen described this year by Paul Sereno of the University of Chicago.”