Sereno, P.C., Tan, L., Brusatte, S., Kriegstein, H.J., Zhao, X., and K. Cloward. 2009. Tyrannosaurid body design first evolved at small body size. Science 325. doi: 10.1126/science.1177428 [Raptorex kriegsteini]

Tyrannosaurid dinosaurs comprised nearly all large-bodied predators (>2.5 tons) on northern continents during the Late Cretaceous. We show that their most conspicuous functional specializations—a proportionately large skull, incisiform premaxillary teeth, expanded jaw-closing musculature, diminutive forelimb, and a hindlimb with cursorial proportions—were present in a new small-bodied, basal tyrannosauroid from Lower Cretaceous rocks in northeastern China. These specializations, scaled up in Late Cretaceous tyrannosaurids with body masses approaching 100 times greater, drove the most dominant radiation of macropredators of the Mesozoic.

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