Dietary plasticity in ungulates: Insight from tooth microwear analysis Florent Rivals a, b, c, * , Gina M. Semprebon d a ICREA, Barcelona, Spain b IPHES, Institut Català de Paleoecologia Humana i Evolució Social, C/ Escorxador s/n, 43003 Tarragona, Spain c Area de Prehistoria, Universitat Rovira i Virgili (URV), Avinguda de Catalunya 35, 43002 Tarragona, Spain d Bay Path College, 588 Longmeadow Street, Longmeadow, MA 01106, USA article info Article history: Available online 7 August 2010 abstract In recent years, tooth microwear has been used as a powerful tool for investigating mammalian diets in paleontological or archaeological contexts. Tooth microwear techniques were applied to a number of late Pleistocene assemblages of bison (Bison antiquus) from North America to analyze bison dietary traits, but more particularly, to test for dietary plasticity of the fossil species compared to their modern rela- tives. Modern bison species are known to be grazers from their ecology. However, the results from tooth wear analysis indicate that dietary traits were more diverse in the fossil bison than in their modern relatives. Bison paleodiets range from pure grazing to mixed feeding. The results illustrate not only the dietary plasticity for that species, but also the potential implications involved when using modern species as analogues for reconstructing the ecology of fossil species. Tooth microwear is a good proxy in archaeological contexts because it gives an insight on the diet of the last days of an animal’s life. The intra-population variability in diet is discussed in relation to the duration of formation of the assem- blages (natural assemblages versus archaeological Paleo-Indian sites). Ó 2010 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction Mammal ecology is frequently investigated through a number of proxies (e.g. locomotion, diet). Insights gained via such proxies are frequently used in paleoenvironmental reconstructions and also for tracking climatic shifts through time (Janis, 1984, 1993, 2003; Vrba, 1988; Aguilar et al., 1999; DeGusta and Vrba, 2005). Morphologic change is one of the most commonly documented responses to ecological changes in the continental fossil record of mammals. Bones and teeth of mammals conveniently preserve important information about two traits e locomotion and diet e both of which play an important role in deciphering the evolu- tionary history of mammals (Janis, 1984, 2003, 2008). Climatic impact on the evolution of mammals is actually a highly complex phenomenon. It seems reasonable to suppose that both climate change and intrinsic biotic controls would have contributed to faunal evolution, although at different temporal scales and magnitudes. Thus, the response of large mammals to climatic changes is usually synchronous but it may also be asynchronous at times. In the latter case, a discrepancy or time lag may exist between climatic events and changes in mammals. Such a discrepancy may not only result from issues involving differences in time scale and temporal resolution but also may be due to the specific proxy used. For example, changes in skull morphology and tooth wear in the extinct artiodactyl group known as the Dromo- merycidae suggested an adjustment in diet during the late Miocene to Pliocene increase in aridity in North America; however, skull morphology apparently lagged behind the apparent dietary shift which was revealed through microwear and mesowear analyses (Semprebon et al., 2004a). Isotope studies reveal that dietary changes may also be more labile than morphologic changes (Feranec, 2007), an insight that may explain the lack of temporal synchronicity between changes in tooth shape and wear (Rivals et al., 2007, 2008; Semprebon and Rivals, 2007, in press; Janis, 2008; Joomun et al., 2008). Similar lags or decoupling between climatic change and various aspects of morphology is very frequently observed in the Pleistocene and Holocene (Kaiser and Franz-Odendaal, 2004; Kaiser and Schulz, 2004; Rivals and Solounias, 2007; Semprebon and Rivals, 2010). It seems evident that speciation events and morphological changes are not necessarily the best ecological proxies, especially when applied to the Quaternary, because morphology (thus speci- ation) requires many generations for a character to be fixed in a population. In the same way, not all species will exhibit changes in their geographic ranges during periods of climatic change (Blois and Hadly, 2009). Therefore, the biotic response of individuals, species, * Corresponding author. IPHES, Institut Català de Paleoecologia Humana i Evo- lució Social, C/ Escorxador s/n, 43003 Tarragona, Spain. Fax: þ34 977 55 95 97. E-mail address: florent.rivals@icrea.es (F. Rivals). Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint 1040-6182/$ e see front matter Ó 2010 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2010.08.001 Quaternary International 245 (2011) 279e284