Tyrannosaurid Skeletal Design First Evolved at Small Body Size:
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.
There's the requisite article in The New York Times, but Ed Yong has a better roundup. As noted by many these finds indicate that the current theories about peculiar anatomical features of T. rex contingent upon its size have to be revised. So scientists were wrong. Now comes another round of theorizing....
