John R. Horner. Museum of the Rockies, Montana State University, Bozeman, Montana 59717-0040. E-mail: jhorner@montana.edu Kevin Padian. Department of Integrative Biology and Museum of Paleontology, University of California, Berkeley, California 94720-3140 Armand de Ricqle `s. E ´ quipe Formations Squelettiques, URA CNRS 11 37, Universite ´ Paris VII, 75251 Paris cedex 05, France, and Colle `ge de France, Paris, France John R. Horner, Kevin Padian, and Armand de Ricqle `s Introduction