Richard A.Fari¿a is Professor of Paleontology at the Facultad de Ciencias, Universidad de la Rep¿blica, Montevideo, Uruguay. He has also published science books for a general readership and collaborated in TV documentaries on the subjects of his expertise.Sergio F. Vizca¿ is Professor of Vertebrate Zoology at the Universidad Nacional de La Plata and researcher of the Consejo Nacional de Investigaciones Cient¿cas y T¿icas working at the Museo de La Plata, Argentina. His research focuses on the paleobiology of South American fossil vertebrates, mostly mammals. He has participated in numerous field work seasons in Argentina and Antarctica. He was the President of the Asociaci¿n Paleontologica Argentina. Gerry De Iuliis is affiliated with the Department of Ecology and Evolutionary Biology at the University of Toronto.