The evolutionary history of Maniraptora, the clade of carnivorous dinosaurs that includes birds and the sickle-clawed Dromaeosauridae, has hitherto been largely restricted to Late Jurassic and Cretaceous deposits on northern continents. The stunning Early Cretaceous diversity of maniraptorans from Liaoning, China, coupled with a longevity implied by derived Late Jurassic forms such as Archaeopteryx, pushes the origins of maniraptoran lineages back to Pangaean times and engenders the possibility that such lineages existed in Gondwana. A few intriguing, but incomplete, maniraptoran specimens have been reported from South America, Africa and Madagascar. Their affinities remain contested, however, and they have been interpreted as biogeographic anomalies relative to other faunal components of these land-masses. Here we describe a near-complete, small dromaeosaurid that is both the most complete and the earliest member of the Maniraptora from South America, and which provides new evidence for a unique Gondwanan lineage of Dromaeosauridae with an origin predating the separation between northern and southern landmasses.
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Acknowledgements We thank the Avelás and Salinas families, C. Muñoz, L. Fernández and the 2004 La Buitrera field crew for their help in the field; J. A. González, P. Chiarelli, M. Brown, J. Holstein, L. Herzog, A. Shinya, C. Van Beek and D. Wagner for preparing the holotype; J. Weinstein for photography, M. H. Donnelly for retouching Fig. 1; J. González for the reconstruction of Buitreraptor; S. de Valais for help and discussion during the early stages of this work; D. Pol for reading the manuscript and providing advice; and F. E. Novas and R. A. Coria for providing access to materials in their care. Fieldwork and preparation was facilitated by the Agencia Cultura of Río Negro Province and supported by The Jurassic Foundation (S.A.) and NASA (P.J.M.), and research was supported by the NSF (P.J.M.).