Paleohistological analysis has been applied to nonhuman bone to provide information on the biological age of animals as well as processes of diagenesis or fossilization (Cook et al. 1962; Sander and Andrassy 2006; Enlow and Brown 1956). Here we report on histological analysis of two specimens of Pleistocene proboscideans from the western interior of North America. These specimens retain elements of the bone microstructure and are from distinct depositional and taphonomic contexts. The comparison of osteon size and density provides information on the biological age at death of these individuals and has the potental to address questions regarding the rate of growth and development of Pleistocene megafauna, This research illustrate the utility of even small fragments of ancient bone for estimating the lifespan and physiological characteristic of Pleistocene fauna as well as for evaluating post depositional processes (Hedges 2002; Jans et al. 2002).