The Beginning of the Age of Mammals

This volume is not for the faint of heart. It’s the real McCoy. The Beginning of the Age of Mammals is the leading textbook on early Cenozoic mammalian evolution available for teaching at the graduate level. It is authoritative, up-to-date, and full of references to corroborate synthetic overviews of major events in mammalian evolution. Ken Rose does his profession a service by providing a compact analysis of the history of the diverse Class Mammalia through the end of the Eocene Epoch and beyond. This book is a welcome, traditional synthesis of mammalian vertebrate paleontology. There are other more topical treatments of Mammalia that are important (e.g., Prothero and Emry, 1996; Janis et al., 1998, 2008; Rőssner and Heissig, 1999), but due to their focus, they are not global in aspect or expansive in geologic time embraced. In one volume, Ken Rose examines the evolution of all mammals during the first part of the “Age of Mammals. ” Necessarily, he examines the evolution of mammals during the “Age of Dinosaurs” as well. Mesozoic treatments are well-researched and presented in concise fashion, to set the stage for interpreting the phenomenal radiations of early Cenozoic mammals throughout the world. Ken admirably covers the globe in examining the Paleocene and Eocene fossil records, and can’t resist discussing Oligocene faunas when relevant. He references Rose and Archibald (2005) for the morphological and molecular bases of recognizing relationships of ordinal level clades, but the latter volume is necessarily restricted to select fossil and extant representatives, without delving into the details of fossils and the fossil record. The Beginning of the Age of Mammals includes an introductory chapter that covers a great range of the current debate on end-Cretaceous extinction, the timing of crown group placental radiation, and recognition of supraordinal groups. Also tackled are classification, polarity and monophyly, geologic time, land mammal ages, paleocontinent geography, and Paleocene-Eocene floras. Ken Rose, the anatomist, pens a chapter on comparative anatomy, providing the basics for terminology used throughout the volume. Following are chapters on non-mammalian cynodonts and a “synopsis of Mesozoic mammal evolution,” which includes multituberculates and their Cenozoic history. A chapter on Metatheria includes Paleogene fossils and their Mesozoic predecessors. For convenience and due to enigmatic ordinal level classification, earliest Eutheria are treated in one short chapter. The diversity of Mammalia, from its early history onward, unites this section of the book. Rose highlights new Mesozoic discoveries, injecting even early 2006 references into the text (e.g., citation of the semiaquatic docodont Castorocauda), but press time ruled out inclusion of the gliding Volaticotherium Meng et al. (2006). These early chapters lead toward chronicling the radiation of Eutheria as reflected in the Paleocene and Eocene fossil record. It seems that the first section of the volume was constructed differently from the remainder; some of the figure captions would benefit from expansion, some of their abbreviations are not given, and there is at least one figure misnumbered (fig. 4.20). Ken Rose tackles Paleogene mammalian diversity first with a chapter on Cimolesta, a subset of Superorder Ferae. Cimolesta includes many extinct groups plus pholidotes, and possibly stem taxa for other radiations. Admittedly then, content of Cimolesta is not stable — but that is science. Pholidotes are saved for treatment with Xenarthra in a later chapter. Pantolestida seem popular recently. Whether the bite of pentacodontid pantolestids could deliver venom seems unlikely according to Folinsbee et al. (2007), and ptolemaiid pantolestids appear to have continued into the Miocene of Africa (Cote et al., 2007), but that revelation emerged too recently for this volume. Rose excels in his presentation of creodonts and carnivorans. His treatment of Insectivora is also excellent, and departs from McKenna and Bell (1997) in including leptictids as sister taxon to lipotyphlans. Obviously, Rose is partial to Archontans, which is shown especially by the thirty pages devoted to Primates. Ungulates are difficult to manage in a book because one has to juggle artiodactyls and whales in the same breath. Also, what do you do with perissodactyls and tethytheres? Well, for a book, you just put them in separate chapters. Cladistically, one must remind the reader that all of these, with South American ungulates, appear to be related to a core radiation of early Cenozoic mammals traditionally called condylarths. In Chapter 12, Ken first expands upon condylarths, one of his favorite groups, plus South American ungulates (but I have to say that typotheres don’t appear to be monophyletic). Tethytheres, including sirenians, proboscideans, and those lovable desmostylians, are one of the more robust higher level taxa. Their unity with hyracoids and perissodactyls is defended by McKenna and Bell (1997) and is accepted in Chapter 13, but called into molecular question and linked with Afrotheria elsewhere (see Rose and Archibald, 2005). All are treated here as Altungulata, but that higher taxon may not stand the test of continued research. Ken’s thorough presentation of the fossil records of these groups is exemplified by his discussion of early perissodactyls, with its informative analysis of their postcranial anatomy. Cete and Artiodactyla follow, and their relationships are explored. Artiodactyla — that diverse taxon with lots of early Cenozoic familylevel groupings — are considered monophyletic here, but alternative relationships with Cete are discussed. Morphological and molecular data converge on the conclusion that Cete are the sister taxon to anthracotheres + hippos. All Paleocene-Eocene artiodactyl groups receive good coverage in this chapter. Pecoran ruminants are one of the mammalian groups that underwent a tremendous Neogene radiation. Although diverse in the early Miocene, many family level groups are unknown in the Paleogene. Consequently, these are barely noted in this volume (and dromomerycids don’t even appear in the classification). Which brings us to Anagalida, the core of which is the Cenozoic radiation of Glires (rodents plus lagomorphs). Anagalida is an inclusive taxon meant to incorporate potential Glires relatives, namely Cretaceous zalambdalestids, early Cenozoic Anagale and Pseudictops, and the living Order Macroscelidea (elephant shrews). Whether any of these has a special relationship with Glires is controversial, and molecular work now argues that Macroscelidea belong with Afrotheria. Rose notes the intriguing idea that macroscelideans share postcranial features with hyopsodontids. Despite the tradition of aligning Glires with the groups noted above, there is little that holds them together, and the evolutionary story here is really that of Glires. This chapter mentions mimotonids and eurymylids, and lagomorphs are covered quickly. Probably we underestimate pre-ochotonid, pre-leporid lagomorph diversity (by the way, generally their incisors are not laterally compressed as they are in rodents). Rodents receive traditional treatment that encapsulates their morphological range, which is reasonable for the allotted space. However, morphologists (see McKenna and Bell, 1997, who attempt to break away from traditional suborders by adding suborders Sciuravida and Anomaluromorpha to Sciuromorpha, Myomorpha, Hystricognatha) and molecular biologists (e.g., Horner et al., 2007, who also distinguish anomalurids) are revolutionizing our notions of how rodents evolved. In a few years, rodent classifications will look entirely different from those of the 20 century. For now, Rose offers a brief global survey of latest Paleocene, Eocene, and some Oligocene rodents, sufficient to underscore diversity, paleobiogeography, and the obvious room for future Journal of Vertebrate Paleontology 29(1):312–313, March 2009 # 2009 by the Society of Vertebrate Paleontology