Primates of modern aspect are characterized by several traits of the skull and postcranium, most notably increased encephalization, olfactory reduction, postorbital bars, larger and more convergent orbits, an opposable hallux, and nails instead of claws on the digits. When, where, how, and why a group of mammals with this distinctive morphology emerged continues to capture the interest of biologists. The past 15 years have witnessed the discovery of numerous well-preserved basal forms and sister taxa from the Paleocene and Eocene of Asia, Africa, North America, and Europe. These new findings are particularly fascinating because they extend the antiquity of several higher-level clades, greatly increase our understanding of the taxonomic diversity of the first Primates, and document a far greater spectrum of variation in skeletal form and body size than noted previously. Not surprisingly, the past decade also has witnessed molecular and paleontological attempts to resolve primate supraordinal relationships. Many of our current notions about the adaptations of the first primates, however, are based on research performed 20-35 years ago—a period when the fossil record was much less complete. For instance, there remains considerable debate over the leaping versus quadrupedal component of early primate locomotion, as well as differing views regarding the function of certain mandibular and circumorbital features in basal primates. Indeed, the absence of a forum for the integration of past, recent, and ongoing research on the origin of primates has greatly hindered a better understanding of the significance of marked anatomical and behavioral transformations during this important and interesting stage of primate evolution. Accordingly, our December 2001 conference and this accompanying edited volume on Primate Origins and Adaptations capitalize on an increasing amount of independent museum, field and laboratory-based research on many important outstanding problems surrounding the adaptive synapomorphies of the earliest primates. Moreover, it couples the emerging views of junior researchers with those who have made significant contributions to the study of early primate phylogeny over the past three decades.
Due to the evident need for a reassessment of primate origins and adaptations, there were two principal goals of our conference and volume. First, we aim to provide a broad focus on adaptive explanations for locomotor and postural patterns, craniofacial form, neuro-visual specializations, life history patterns, socioecology, metabolism, and biogeography in basal primates. Second, to offer an explicit evolutionary context for the analysis of major adaptive transformations, we aim to provide a detailed morphological and molecular review of the phylogenetic affinities of basal primates relative to later primate clades, as well as other mammalian orders. As Plesiadapiformes have figured so heavily in discussions of primate origins, this, and the focus of our volume on adaptive scenarios, helps to explain the overt emphasis on the evolution of anatomical features. Therefore, in addition to strictly systematic or paleonto-logical questions regarding primate origins, we concentrate primarily on the adaptive importance of unique primate characters via a comprehensive consideration of anatomical, behavioral, experimental, and ecological investigations of primate and nonprimate mammals. In this regard, a phylogenetic framework is critical for detailing the functional and evolutionary significance of specific character states and morphological complexes. Given ongoing debate regarding the appropriate content of the taxon Primates, we have decided to let authors use the terms Primates and Euprimates as they see fit. The meaning is usually obvious from the context. Likewise, for the tooth-combed lemurs, we have let authors use the spelling Strepsirrhini or Strepsirhini as they choose.
Since an increasingly evident fact about the earliest primates is their very diminutive body size, another important related goal is to characterize those adaptive trends, morphological features, and behaviors which vary and covary allometrically. Obviously, this has figured heavily in certain explanations for the evolution of grasping appendages in small-bodied basal primates. In addition, the negative allometry of neural and orbital size, coupled with relatively larger convergent orbits, has important structural consequences for explaining increased orbital frontation and the correlated evolution of a postorbital bar at small skull sizes. Perhaps the most important contribution of our volume to bioanthropology and paleontology is that it develops a forum for evaluating past and current research on primate origins. In doing so, we directly address a series of competing long-standing scenarios regarding the adaptive significance of important primate synapomorphies. By examining hypotheses that have dominated our notions regarding early primate evolution and coupling this with an emergent body of novel evidence due to fossil discoveries, as well as technological and methodological advances, our edited volume will provide a long overdue multidisciplinary reanalysis of a suite of derived life history, socioecological, neural, visual, circumorbital, locomotor, postural, and masticatory specializations of the first primates. This integrative neontological and paleontological perspective is critical for understanding major behavioral and morphological transformations during the later evolution of higher primate clades.
This volume collects a wide-ranging series of contributions by experts actively performing novel research relevant to the adaptive synapomorphies of the Order Primates. The authors and original conference participants are identical due to the enthusiastic response of each. For this reason, we gather together virtually every researcher, or one of their former graduate students, currently performing important research relevant to primate origins and adaptations. The series of chapters are divided into the following sections: The Supraordinal Relationships of Primates and Their Time of Origin; Adaptations and Evolution of the Cranium; Adaptations and Evolution of the Postcranium; Adaptations and Evolution of the Brain, Behavior, Physiology, and Ecology. The contents of each chapter are briefly as follows:
Springer et al. address the molecular data regarding primate supra- and infraordinal affinities. Soligo et al. reassess the antiquity and biogeography of primates and related mammals. Sargis considers the implications of tree shrew postcranial morphology for understanding early primate phylogeny. Godinot similarly stresses the importance of tree shrews for understanding primate origins. Silcox reexamines the fossil evidence regarding primate-plesiadapiform affinities. Ross et al. examine the evidence for activity patterns of early Primates. Ravosa et al. and Heesy et al. discuss comparative and experimental data regarding circumorbital form and function in primates and other vertebrates. Vinyard et al. integrate novel in vivo and morphological evidence regarding masticatory form and function in archontans and primates. Lemelin and Schmitt provide novel information about cheiridial morphology and performance in a series of primate and nonprimate mammals. Hamrick discusses the basis of evolvability of the mammalian autopod with special reference to the evolution of digital proportions in primates. Cartmill et al. consider the novelty and significance of primate diagonal gaits among mammals. Larson examines kinematic and skeletal evidence regarding forelimb adaptations unique to primates. Bloch and Boyer discuss the important implications of previously unknown North American plesiadapiform postcrania for understanding the evolution of basal primate locomotor adaptations. Szalay reviews the philosophy of model construction in primate locomotor evolution. Dagosto considers the evidence regarding locomotor adaptations of ancestral primates. Shea investigates the evolution of encephalization in archontans vis-à-vis life history, ecological, and allometric factors. Preuss employs neuroanatomical data to provide insight into neural specializations of the primate visual system. Mueller et al. employ a systematic analysis of extant primates to consider the evolution of basal primate social systems. Snodgrass et al. review the evolutionary and adaptive significance of variation in metabolic rate in the evolution of brain size. Yi and Li evaluate examples of protein evolution during primate evolution. Sussman and Rasmussen review the ecological underpinnings of early primate adaptations in marsupial analogs. Lucas et al. analyze the relation between dietary evolution and color vision. Apart from a consideration of new fossil discoveries and their direct relevance to outstanding issues regarding the evolution of the locomotor apparatus in early primates, these presentations represent a significant increase in the wealth of kinematic and developmental data aimed at the question of primate origins.
Numerous individuals and institutions have contributed greatly to the success of our conference and this accompanying edited volume. On the publishing end, the following at Springer/Kluwer are thanked for their support, diligence, and patience—Andrea Macaluso, Krista Zimmer, Joanne Tracey, as well as the series editor Russ Tuttle (University of Chicago). Our international conference benefited significantly from the financial support of the WennerGren Foundation for Anthropological Research, Physical Anthropology Program of the National Science Foundation, Field Museum of Natural History (especially the Mammals Division), and Department of Cell and Molecular Biology at Northwestern University Feinberg School of Medicine. The following individuals are singled out for providing unique assistance with the organization and implementation of our conference—Bill Stanley, Bruce Patterson, Larry Heaney, Bob Martin, Bob Goldman, and Gail Rosenbloom. The following graduate students offered technical and logistical help that ensured the symposium went off without a hitch—Aaron Hogue, Kristin Wright, Barth Wright, and Kellie Heckman. Lastly, and most importantly, we thank our spouses—Sharon Stack and Dan Gebo—for their continued support and our respective children—Nico and Luca, and Anne Marie—for inspiration.
Matthew J. Ravosa Marian Dagosto
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