Tyrannosaurid Skeletal Design First Evolved at Small Body Size

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Science  16 Oct 2009:
Vol. 326, Issue 5951, pp. 418-422
DOI: 10.1126/science.1177428

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Diddy Dinosaurs

Tyrannosaurs were the dominant large dinosaur predator during the Late Cretaceous. They have several distinct specialized features, including an oversized skull, huge hindlimbs, and tiny arms, that have been thought to have evolved in concert with their large size and carnivorous diet. Sereno et al. (p. 418, published online 17 September; see the Perspective by Clark) now describe an earlier, diminutive tyrannosaur from China that also has these common specializations. Thus, these features were not a result of size increase but appear to have been required for feeding efficiency at all sizes.


Nearly all of the large-bodied predators (>2.5 tons) on northern continents during the Late Cretaceous were tyrannosaurid dinosaurs. We show that their most conspicuous functional specializations—a proportionately large skull, incisiform premaxillary teeth, expanded jaw-closing musculature, diminutive forelimbs, and hindlimbs with cursorial proportions—were present in a new, small-bodied, basal tyrannosauroid from Lower Cretaceous rocks in northeastern China. These specializations, which were later 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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