The biogeochemistry of the aucilla river fauna

Abstract

Ecosystems in the late Pleistocene differed dramatically from the ones we know today, particularly in their striking diversity and abundance of large mammals. North America alone supported a wide range of now globally or locally extinct taxa, including several families of proboscideans, giant ground sloths, glyptodonts, equids, camelids, and tapir, as well as surviving taxa such as deer and bison (Kurtén and Anderson, 1980). Although reconstructing fossil ecosystems is often problematic, the survival of some Pleistocene species allows us to compare paleobiological reconstructions with modern observations. We can thus assess the precision of any proxy used, which in turn allows us to evaluate the accuracy of paleoecological reconstructions.Accurately reconstructing the biology of extinct taxa is essential not only for assessing paleoecological relationships, but also for evaluating many extinction hypotheses. Historically, two opposing sets of theories have been argued to explain the Pleistocene extinction. One set of theories blames this extinction directly on human hunters (e.g. Churcher, 1980; Martin, 1984), while the other invokes climatic and/or ecological changes associated with deglaciation (e.g. Graham and Lundelius, 1984; Guthrie, 1984). More recently, it has been suggested that extinctions resulted from the combined stress of hunting and ecological changes, some of which may have been indirectly caused by early humans (Owen-Smith, 1988; Haynes, 1991; Miller et al., 1999). Researchers on all sides of this debate frequently make complex assumptions about the biology of extinct fauna, many of which cannot be tested using traditional morphological or taphonomic methods. The Aucilla River fauna, with its abundance of well-preserved specimens from both late glacial and full glacial times, provides an unprecedented opportunity to test several theories about the paleoecology of extinct species. We analyzed the chemistry of tooth enamel from several extinct taxa, including equids, llamas, mammoths, mastodons, and tapir, as well as from deer, which have survived into the present. The stable isotope ratios of carbon (ä13C) were used to reconstruct the diets of each individual and the degree of dietary specialization of each species. Oxygen isotope ratios (ä18O) were used to examine climatic variability. Finally, strontium isotope ratios (87Sr/86Sr) were used to examine the migration patterns of mammoths and mastodons.