A Comparison of Methods for the Probabilistic Determination of Vertebrate Extinction Chronologies

Abstract

Much effort has been directed toward determining the extinction dates of late Quaternary megafaunal mammals, usually in the context of testing models of anthropogenic “overkill” or terminal Pleistocene climatic change. These studies have typically relied on searching for the youngest reliable date (e.g., Long and Martin, 1974), or on matching the mode of a sequence of dates to the time of presumed anthropogenic impact (e.g., Martin, 1986). Little attention appears to have been paid to the determination of vertebrate extinctions dates by probabilistic methods, although a number of authors have treated the related problem of determining invertebrate fossil taxon ranges in biostratigraphical analysis (e.g., Hay, 1972; Strauss and Sadler, 1989; Gilinsky and Good, 1991), and Badgley (1990) has addressed the importance of statistical evaluation of the relationship between sample size and apparent extinctions in the Eocene vertebrate record. Here, I use Monte Carlo simulation to compare the performance of two published probabilistic techniques and a third technique developed here that is based on median stratigraphic gap length in estimating the 95% confidence interval relative to a known extinction date. When applied to a sample of the published record of radiocarbon dates, these techniques indicate that the current database is inadequate to constrain the “late Pleistocene” megafaunal extinction event(s) to the narrow chronological window required by the “blitzkrieg” anthropogenic overkill model (but see Alroy, this volume; Martin and Steadman, this volume). Although this result is not disconfirmatory of the blitzkrieg model, it does argue for the necessity of continuing to improve the data base of published radiocarbon dates.