The Beginning of the Age of Mammals in South America, Part III

Abstract

The great cliff (Gran Barranca) south of Lago ColhueHuapi in southern Chubut, Argentina exposes nearly 25million years of sediments, from about 40 mya to18 mya. Gaps exist in this record, of course, and someintervals are more fossiliferous than others, but GranBarranca has been—and continues to be—one of themost important fossil localities in South America. It alsowas formative in the career of one of paleontology’sgreat thinkers: George Gaylord Simpson. Simpson madetwo expeditions to collect fossils at Gran Barranca andother Patagonian localities, and he later published twomassive and enduring works on mammals from GranBarranca and other Paleogene localities: The beginningof the age of mammals in South America, Parts I and II(Simpson 1948, 1967). The Paleontology of GranBarranca, edited by Richard Madden and a team ofcollaborators, follows in the tradition of Simpson in itsgoal of synthesizing knowledge of this important localityand what it indicates about the development of mammalfaunas in South America.This book is an edited volume of 29 chapters intendedfor an academic audience. Forty-five experts contributed asauthors or co-authors. The production quality of the volumeis excellent overall, and references are included at the endof each chapter rather than as a single section at the end ofthe book. There is a comprehensive taxonomic index,which I found to be very handy.The opening chapter introduces the reader to GranBarranca and the history of its discovery and exploration.It is a thoroughly researched historical narrative and one ofthe most enjoyable chapters in the book. It also offers novelinsights into who might have discovered this importantlocality.Part I, Geology, includes three chapters that addressthe physical stratigraphy, magnetostratigraphy, and geo-chronology of Gran Barranca. They together provide adetailed description of the geological and chronologicalcontexts of Gran Barranca. Seven faunal levels areidentified. Most of these faunal levels correspond topreviously recognized South American Land Mammal“Ages,” but two new intervals are noted: one betweenlevels pertaining to the Tinguirirican and DeseadanSALMAs and the other at the top of the sequence,above levels referable to the Colhuehuapian SALMA.The recognition of a post-Tinguirirican, pre-Deseadaninterval is intriguing and suggests that not all faunaspreviously considered to be Deseadan in age may in factpertain to the late Oligocene. The new absolute ageestimates provided for this and other intervals at GranBarranca provide extremely useful new data that willfacilitate both inter- and intracontinental correlations.Part II, Systematic Paleontology, includes a dozenchapters of varying scope, mostly focusing on mammals.Some chapters review and revise a restricted taxonomicgroup over the entire span of the Gran Barranca sequence.Others discuss a broader taxonomic group over a morerestricted temporal interval. A few are quite circumscribedand center on a single species or group from one faunalinterval. Many new genera and species are described, and