THIS BOOK IS THE OUTCOME of a decade-long project that began when Robert Harrington, then the science editor for the Johns Hopkins University Press, invited me to write a book on fossil mammals. The need for such a book became apparent from a graduate seminar in mammalian evolution I have taught over the past 20 years at the Johns Hopkins University. While we have witnessed the primary literature in the field increase at an astonishing pace, it became evident that there was a real dearth of general books on the subject. Except for Savage and Long's (1986) Mammal Evolution (which is now outdated and gave only a superficial account of many Paleogene groups), there was no available book that synthesized basic data on the extant mammals together with a survey of the rapidly improving mammalian fossil record to provide an overview of mammalian evolution. The Beginning of the Age of Mammals is intended to help fill this void by presenting an in-depth account of current knowledge about mammalian evolution in the Early Cenozoic. It is designed to provide both graduate and undergraduate students with a comprehensive summary of the diversity and rich history of mammals, focusing on the early radiations of living clades and their archaic contemporaries. I hope it may serve as a useful reference for professionals as well.

This is a book about fossils. The focus is on the anatomy preserved in the fossil record, and what it implies about relationships, phylogeny evolution, behavior, paleo-ecology, and related issues. Other topics, such as geology, paleoflora, climate, and molecular systematics are discussed where they are pertinent, but they are subsidiary to the principal objective, which is to summarize the mammalian fossil record. I have chosen to concentrate on the Early Cenozoic part of that record not just because that is my personal interest, but also because it is the most critical part of the fossil record xii

Preface with regard to the origin and early adaptive radiations of almost all the major clades of extant mammals. Furthermore, substantial recent advances in our knowledge of mammals during this pivotal interval make this summary timely

I have endeavored to survey the literature through the end of 2004 and have added a few particularly pertinent references that are more recent, in order to furnish a review of all higher taxa of Paleocene and Eocene mammals that is as current as possible. Treatment of different groups is unavoidably uneven, a reflection of multiple factors, including the Early Cenozoic diversity of particular groups, the interest level they have generated, and the intensity at which they have been studied, especially recently. Judgments had to be made as to what was significant enough to be included in a review of this sort and where to include more detail. I hope there have not been serious omissions. I have borrowed liberally from the classification and range data presented by McKenna and Bell (1997, 2002) and have benefited greatly from their vast experience. Although I have not always agreed with their arrangement (and have noted in the text where modifications were necessary), their monumental compilation provided the essential framework, without which this book would have been far more difficult to achieve.

One of the most important aspects of this kind of book is the quality and scope of illustrations. Rather than prepare new figures or redraw existing ones in an attempt at uniformity I opted to reproduce the best available illustrations of a wide diversity of fossil mammals. The drawback of this approach is that multiple styles of illustration are often combined in the same composite figure. However, I believe the benefit of using original illustrations significantly outweighs the aesthetic of redrawing them all in the same style, with its inherent risk of introducing inaccuracies. For ease of comparison, I have taken liberties in sizing and reversing many images, with apologies to the original artists for anomalies of lighting that may result. I have tried to illustrate at least one member of each Early Cenozoic family (except a few obscure families, and some families of the highly diverse artiodactyls and rodents). Figures were selected to give readers an impression of the diversity of fossil mammals, the state of the evidence, and the most important specimens or taxa.

Throughout the book, my goal has been not just to present current interpretations of the mammalian fossil record but also to highlight the quality of the evidence and analyses on which these inferences are based. I have tried to indicate where the data are particularly sound and convincing, as well as where the evidence is more tenuous or ambiguous. The latter examples should be especially fruitful areas for further research.

I hope that I have been able to impart some of my enthusiasm for mammalian paleontology, and to demonstrate that fossils are not just curiosities but are the key to understanding the extraordinary history of life. George Gaylord Simpson perhaps best captured the allure of paleontology in his classic Attending Marvels, recounting his 1930-1931 Scar-ritt Expedition to Patagonia in search of fossil mammals (Simpson, 1965: 82):

Fossil hunting is far the most fascinating of all sports. I speak for myself, although I do not see how any true sportsman could fail to agree with me if he had tried bone digging. It has some danger, enough to give it zest and probably about as much as in the average modern engineered big-game hunt, and the danger is wholly to the hunter. It has uncertainty and excitement and all the thrills of gambling with none of its vicious features. The hunter never knows what his bag may be, perhaps nothing, perhaps a creature never before seen by human eyes. Over the next hill may lie a great discovery! It requires knowledge, skill, and some degree of hardihood. And its results are so much more important, more worth while, and more enduring than those of any other sport! The fossil hunter does not kill; he resurrects. And the result of his sport is to add to the sum of human pleasure and to the treasures of human knowledge.

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