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Science 7 September 2007:
Vol. 317. no. 5843, pp. 1378 - 1381
DOI: 10.1126/science.1144066
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Reports

A Basal Dromaeosaurid and Size Evolution Preceding Avian Flight

Alan H. Turner,1* Diego Pol,2 Julia A. Clarke,3,4,1 Gregory M. Erickson,5 Mark A. Norell1

Fossil evidence for changes in dinosaurs near the lineage leading to birds and the origin of flight has been sparse. A dinosaur from Mongolia represents the basal divergence within Dromaeosauridae. The taxon's small body size and phylogenetic position imply that extreme miniaturization was ancestral for Paraves (the clade including Avialae, Troodontidae, and Dromaeosauridae), phylogenetically earlier than where flight evolution is strongly inferred. In contrast to the sustained small body sizes among avialans throughout the Cretaceous Period, the two dinosaurian lineages most closely related to birds, dromaeosaurids and troodontids, underwent four independent events of gigantism, and in some lineages size increased by nearly three orders of magnitude. Thus, change in theropod body size leading to flight's origin was not unidirectional.

1 Division of Paleontology, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024–5192, USA.
2 CONICET, Museo Paleontológico Egidio Feruglio, Avenida Fontana 140, (9100) Trelew, Argentina.
3 Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Campus Box 8208, Raleigh, NC 27695–8298, USA.
4 Division of Paleontology, North Carolina Museum of Natural Sciences, 11 West Jones Street, Raleigh, NC 27601–1029, USA.
5 Department of Biological Sciences, Florida State University, Dewey Street and Palmetto Drive, Tallahassee, FL 32306–1100, USA.

* To whom correspondence should be addressed. E-mail: turner{at}amnh.org

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