The order Rodentia is the most abundant and successful group of mammals, and it has been a focal point of attention for compar­ ative and evolutionary biologists for many years. In addition, rodents are the most commonly used experimental mammals for bio­ medical research, and they have played a central role in investi­ gations of the genetic and molecular mechanisms of speciation in mammals. During recent decades, a tremendous amount of new data from various aspects of the biology of living and fossil rodents has been accumulated by specialists from different disciplines, ranging from molecular biology to paleontology. Paradoxically, our understanding of the possible evolutionary relationships among different rodent families, as well as the possible affinities of rodents with other eutherian mammals, has not kept pace with this information "explosion. " This abundance of new biological data has not been incorporated into a broad synthesis of rodent phylo­ geny, in part because of the difficulty for any single student of rodent evolution to evaluate the phylogenetic significance of new findings from such diverse disciplines as paleontology, embryology, comparative anatomy, molecular biology, and cytogenetics. The origin and subsequent radiation of the order Rodentia were based primarily on the acquisition of a key character complex: specializations of the incisors, cheek teeth, and associated mus­ culoskeletal features of the jaws and skull for gnawing and chewing.

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Origin and Eutherian Affinities of Rodentia.- The Order Rodentia: Major Questions on Their Evolutionary Origin, Relationships and Suprafamilial Systematics.- Possible Phylogenetic Relationship of Asiatic Eurymylids and Rodents, with Comments on Mimotonids.- Cranial Evidence for Rodent Affinities.- Rodent and Lagomorph Morphotype Adaptations, Origins, and Relationships: Some Postcranial Attributes Analyzed.- Enamel Structure of Early Mammals and Its Role in Evaluating Relationships among Rodents.- Reconstruction of Ancestral Cranioskeletal Features in the Order Lagomorpha.- A Phylogeny of Rodentia and Other Eutherian Orders: Parsimony Analysis Utilizing Amino Acid Sequences of Alpha and Beta Hemoglobin Chains.- Superordinal Affinities of Rodentia Studied by Sequence Analysis of Eye Lens Protein.- Superordinal and Intraordinal Affinities of Rodents: Developmental Evidence from the Dentition and Placentation.- Phyletic Relationships Among Rodent Higher Categories.- Possible Evolutionary Relationships among Eocene and Lower Oligocene Rodents of Asia, Europe and North America.- Cranial Foramina of Rodents.- Phylogenetic Analysis of Middle Ear Features in Fossil and Living Rodents.- Systematic Value of the Carotid Arterial Pattern in Rodents.- Homologies of Molar Cusps and Crests, and Their Bearing on Assessments of Rodent Phylogeny.- Evolutionary Trends in the Enamel of Rodent Incisors.- Rodent Macromolecular Systematics.- Specific Problems of Intraordinal Relationships.- Reproductive and Chromosomal Characters of Ctenodactylids as a Key to Their Evolutionary Relationships.- The Relationships, Origin and Dispersal of the Hystricognathous Rodents.- Myology of Hystricognath Rodents: An Analysis of Form, Function, and Phylogeny.- Amino Acid Sequence Data and Evolutionary Relationships among Hystricognaths and Other Rodents.- New Phiomorpha and Anomaluridae from the Late Eocene of North-West Africa: Phylogenetic Implications.- Problems in Muroid Phylogeny: Relationship to Other Rodents and Origin of Major Groups.- Origin and Evolutionary Relationships among Geomyoids.- Evolutionary Data on Steppe Lemmings (Arvicolidae, Rodentia).- Karyotype Variability and Chromosome Transilience in Rodents: The Case of the Genus Mus.- Electromorphs and Phylogeny in Muroid Rodents.- Concluding Remarks.- Evolutionary Relationships among Rodents: Comments and Conclusions.- Contributors.