Newly discovered Raptorex
gets underfoot of its nearly identical, though a hundred times heavier, descendant, T. rex
in an artist's conception. The tiny T. rex
ancestor is not known to have lived alongside its titanic ancestor.
find, announced September 17, 2009, runs counter to previous theories, which had said that stumpy arms were a relatively recent evolutionary development for T. rex.
Prior to Raptorex,
said paleontologist Thomas Holtz of the University of Maryland, "we didn't know where and when in the history of the tyrannosaurs this arm-shortening occurred."
Illustration courtesy Todd Marshall