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Originally published in Science Express on 17 September 2009
Science 16 October 2009:
Vol. 326. no. 5951, pp. 418 - 422
DOI: 10.1126/science.1177428
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Reports

Tyrannosaurid Skeletal Design First Evolved at Small Body Size

Paul C. Sereno,1,* Lin Tan,2 Stephen L. Brusatte,3 Henry J. Kriegstein,4 Xijin Zhao,5 Karen Cloward6

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.

1 Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637, USA.
2 Long Hao Institute of Geology and Paleontology, Bureau of Land and Resources, 010010 Hohhot, People’s Republic of China (PRC).
3 Division of Paleontology, American Museum of Natural History, New York, NY 10024, USA.
4 3 Evergreeen Lane, Higham, MA 02043, USA.
5 Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 100044 Beijing, PRC.
6 Western Paleontological Laboratories, Lehi, UT 84043, USA.

* To whom correspondence should be addressed. E-mail: dinosaur{at}uchicago.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Becoming T. rex.
J. Clark (2009)
Science 326, 373-374
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