Book Contents And Format

We (see photo above) have endeavored to make this book as comprehensive as possible, within practical limitations.

Of the 15 chapters that follow, four (chapters 1-3 and 15) are of a general nature and apply to the full spectrum of early mammals, whereas the remaining 11 chapters deal with the anatomy, paleobiology, and systematics of the particular groups of mammals known from the Mesozoic, extinct and extant. In chapter 1, we provide some general background on mammals within the context of non-mammalian synapsids; on the successive radiations, biology, and ecological roles of mammals during their tenure of 155 million years (Ma) in the Mesozoic; on the history of study, including a summary of major advances in the past two decades; and on major conceptual issues, past and present.

Chapter 2, "Distribution," presents an account of Meso-zoic mammals in space and time, summarizing their geological and geographical occurrences worldwide. Localities (or, in the case of local faunas, core areas) are plotted on generalized maps, and brief descriptions cover fossil yield, preservation, and diversity for each locality. Faunal lists are summarized in tables that include each site, and synoptic charts show the distribution of sites in time through the Mesozoic, continent-by-continent. The nature and amount of contextual information for published occurrences of Mesozoic mammals is highly variable; where possible, we have tried to give a brief account of depositional context and possible paleoenvironment. Finally, we comment briefly on any patterns of distribution, in both space and time, and their potential implications.

Chapter 3, "Origin of Mammals" provides an in-depth look at one of the fundamental aspects of mammalian evolution: their origin from among the nonmammalian synapsids. Using a phylogenetic and functional perspective, we treat each major anatomical system in the skull and postcranial skeleton, addressing the evolution of mammal-like characters among advanced cynodonts, appearance of mammalian characters at the cynodont-mammal transition, and transformation of character complexes among the earliest mammals. Finally, chapter 15, "Interrelationships of Mesozoic Mammals," gives a summary of the phylogenetic relationships among the individual groups of early mammals covered by the 11 systematic survey chapters. We discuss the often controversial relationships among the principal groups of mammals (illustrated by two alternative trees) and present a synthetic phylogeny that incorporates the full range of diversity among Mesozoic mammals, together with a sampling of the major living groups—monotremes, marsupials, and placentals. This chapter is based largely on the morphological data we have collected from all these Mesozoic mammal groups through our own observations and from the literature, as summarized in our recent study (Luo et al., 2002) and incorporates the results of a new parsimony analysis that includes additional taxa.

Mammalian phylogeny is the principle we have abided by for the book's organization. The sequence of the remaining 11 systematic survey chapters of major kinds of Mesozoic mammals follows the mammalian family tree presented in chapter 15. Each systematic survey chapter on a given group of Mesozoic mammals includes a brief characterization, an account of geologic and geographic distribution, comparative anatomy, paleobiology, and sys-tematics. These chapters differ conspicuously in size, owing to the great variation in the number of described taxa and anatomical representation. The shortest of these, chapter 14, treats the poorly known, highly specialized Gondwanatheria, represented by only a few fossils and fewer described taxa. By far the longest chapter, "Allothe-rians" (chapter 8) includes the most diverse and incomparably best known of Mesozoic mammals—the multi-tuberculates. Chapter length thus reflects, in part, limitation by chance representation in the fossil record, but probably, more importantly, it reflects real differences in the extent to which various groups flourished or floundered over the course of Mesozoic time.

A few comments on the systematics of chapters 4-14 are in order. As noted in chapter 1, the book's structure and the basic topology of the mammalian tree made it impractical to restrict the contents of chapters 4-14 to strictly monophyletic units; hence, some chapters deal with convenient sections of the tree, as delineated by the phylogeny of chapter 15. Chapter 4, "The Earliest-Known Stem Mammals," for example, covers Sinoconodontidae, Morganucodonta, and some genera of early mammals that clearly do not belong to either of these groups, but nonetheless are most appropriately treated with them. To emphasize this point and to make clear what is included in a given chapter, a small logo with a simplified mammalian tree appears on the first page of each of these chapters. Branches or clades covered in a chapter are indicated by boldfacing the appropriate part(s) of the mammalian tree. The names of paraphyletic groups cited in the book are given in quotation marks, for example, "sym-metrodontans" or "eupantotherians."

The "Systematics" sections of chapters 4-15 include either stem- or node-based definitions, together with diagnoses for all relevant higher-rank taxa, with diagnoses extending down to the genus level. Type and referred species (those of Mesozoic age) are listed for all genera, and the literature cited (at the end of the book) gives the primary reference for each taxonomic name, down to the species level. We have included all taxa that were published as of March 31, 2002. Although we were unable to include all taxa published after that date, we have cited some papers published thereafter, in such cases as they were available to us while in press. New references published in the interval between April 1, 2002, and January 3, 2004, are listed as "Additional References" and follow the reference list.

Excepting only a few poorly known genera of doubtful status, for which no intelligible published illustration exists, all genera of Mesozoic mammals are illustrated here. Chapters 4-14 all include a table presenting a classification of the taxa covered. Relationships within groups of Mesozoic mammals are reasonably well understood in only a few cases. In order to avoid the implication of some preferred, within-group phylogenetic arrangement, we adopted a neutral system of arrangement whereby subordinate taxa are listed alphabetically within groups (except for type genus and type species, which are listed first under family- and genus-level headings, respectively). If, however, the described group has been recently revised and a phylogeny proposed, we follow the recently published phylogenetic scheme (e.g., some groups discussed in chapters 8 and 10). For the same reason, most of these chapters do not contain cladograms of the groups treated therein. An exception to this is chapter 8, for which we were able to include a hypothesis of relationships among higher taxa of multituberculates on the basis of recent work by Kielan-Jaworowska and Hurum (2001).

We call attention to the fact that some Mesozoic mammals are of uncertain or debatable affinities. Placing such forms among the chapters of this book called for arbitrary decisions, based on anatomical and historical considerations as well as varied opinions in the literature. "Obtuse-angled symmetrodonts," for example, could be variously placed: Kuehneotheriidae among stem mammals (chapter 4) or "symmetrodontans" (chapter 9), and Woutersiidae among stem mammals, "symmetrodontans," or docodon-tans (chapter 5). In each case, we have attempted to cross-reference among chapters and to point out alternative placements.

It will come as no surprise that preparation of this volume involved consultation of many references. This necessitated the adoption of some conventions, mainly aimed at streamlining or clarifying in-text literature citations. Most multiple-authored papers are cited in the text using the convention "et al." (e.g., Novacek et al., 1997). In the case of same-year, multiple-authored papers with the same first author, text citations list enough of the authors to distinguish the references (e.g., Cifelli, Gardner, et al., 1997 versus Cifelli, Kirkland, et al., 1997). There are a few cases of single- or first-authored works by different individuals bearing the same surname (e.g., Bonaparte, C. L., and Bonaparte, J. F.). In practically all cases, dates of pub lication fortunately do not overlap (as in the example given, where more than a century separates the respective published works) and initials of given names are omitted from in-text citations (although initials are used when the author's name is formally included as part of a taxonomic name). An exception to this occurs with E. F. Freeman and P. W. Freeman, both of whom are cited for works published in 1979; here we have included initials of given names in the in-text citations. We cite the published (Latinized) rather than the christened version of the name for the founder of modern systematic botany and zoology, Karl von Linné (e.g., Linnaeus, 1758,1766).

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