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Fossils of two never-before-seen species of tyrannosaur are overturning long-held ideas about the diversity and evolution of this family of dinosaurs. One is an unusually slender, eight-horned tyrannosaur named Alioramus altai, unveiled by AMNH Chair of Paleontology Mark Norell and AMNH/Columbia University PhD student Stephen Brusatte. The other is an ancient, tiny version of Tyrannosaurus rex called Raptorex kriegsteini, recently described by University of Chicago paleontologist Paul Sereno.