INTRODUCTION

As the many contributions to this volume reflect, Charles A. Repenning ('Rep') is recognized widely as having made significant contributions in disparate disciplines of the geosciences. From his early career as a geologist studying and mapping extensive areas of the western United States, to his 'second' career addressing the evolutionary history of pinniped mammals, and his tangential studies of other mammal groups (e.g., shrews), Rep left a published record of data, thoughts, ideas, and suggestions that will stimulate geologists and paleontologists for many decades.

Most of our interactions with Rep centered on his third major research focus, the evolutionary history and biochronology of arvicoline rodents (voles, lemmings, muskrats, and their extinct kin). His contributions in this area were substantial and extend well beyond mere collection and identification of specimens and descriptions of new taxa. Rep's approach to his data (and those of other workers) often was controversial, and sometimes confrontational. He was passionate about his work, and could be obstinate, cantankerous, and caustic in interactions with colleagues and students, but his ideas and criticisms were almost universally stimulating. He was a prolific and inveterate correspondent. One of us (CJB) maintained a running postal (and subsequently, email) correspondence with Rep from 1990 through 2004, ending shortly before his murder. The correspondence encompasses hundreds of pages of material and is preserved (along with additional Repenning correspondence) in the Repenning Correspondence Archives of the Vertebrate Paleontology Laboratory at The University of Texas at Austin. Rep used his correspondence to develop ideas, to clarify thoughts, and to frame arguments. Much of what he published on arvicolines in the last decade of his life is revealed in inchoate form in his letters, and he openly admitted that this was his practice. In 1993 he wrote "Don't knock yourself out (or your car) to get here, we can always write letters. Gives me something to publish" (Repenning, letter to Christopher Bell, 22 July, 1993, p. 2). Our recent perusal of the correspondence files, combined with a review of his published works on arvicolines, provides an unparalleled opportunity to explore his thoughts about, and approaches to, the evolutionary history, biostratigraphy, and biogeography of extant and extinct arvicolines. The methodological and philosophical approaches under which he considered his work had enormous impacts on his results and the interpretations he drew from those results. We attempt to provide a broader perspective on Rep's work on arvicolines by summarizing the history and development of his ideas on arvicoline biochronology and elucidating some of the insights, assumptions, and underlying thought processes that influenced much of his research.