Key words: : Dinosauria, Sauropodomorpha, Prosauropoda, phylogeny, paleobiogeography, Jurassic, Hanson Formation, Antarctica.

Nathan D. Smith smithnd@uchicago.edu, Committee on Evolutionary Biology, University of Chicago, 1025 E. 57th Street, Culver 402, Chicago, IL 60637, USA; and Department of Geology, The Field Museum of Natural History, 1400 S. Lake Shore Drive, Chicago, IL 60605, USA; Diego Pol dpol@mef.org.ar, CONICET, Museo Paleontológico Egidio Feruglio, Av. Fontana 140, Trelew 9100, Chubut, Argentina.