Revisiting old bones: coupled carbon isotope analysis of bioapatite and collagen as an ecological and palaeoecological tool M.T. CLEMENTZ 1y , K. FOX-DOBBS 2,3,4 * , y , P.V. WHEATLEY 4y , P.L. KOCH 4 and D.F. DOAK 3 1 Department of Geology and Geophysics, University of Wyoming, Laramie, WY, USA 2 Department of Geology, University of Puget Sound, Tacoma, WA, USA 3 Department of Zoology and Physiology, University of Wyoming, Laramie, WY, USA 4 Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA, USA Isotopic studies of palaeoecological and ecological questions often use bone collagen or bioapatite as substrates, but rarely both. Substantial new information can be gained from the incorporation of isotopic values from both the organic and inorganic fractions of bone. Here we show that combining isotopic data from both substrates provides valuable and unique insights into (1) trophic relationships and dietary interactions; (2) differences in digestive physiologies and (3) identification of palaeonto- logical or archaeological remains that lack diagnostic morphological characters. We present a range of new isotopic data collected from modern and fossil mammals, and investigate patterns within several published datasets. We define carbon isotope spacing variables, and then explore four diverse palaeoecological and ecological case studies. Copyright # 2009 John Wiley & Sons, Ltd. Received 14 January 2009; accepted 4 June 2009 KEY WORDS stable isotope; palaeoecology; bioapatite; megafauna; marine mammal; trophic level; carnivore Supporting supplementary information may be found in the online version of this article. 1. INTRODUCTION Stable carbon isotope analysis of fossils is an important method for gathering dietary and environmental information in terrestrial and aquatic ecosystems (Kohn and Cerling 2002; Ambrose and Krigbaum 2003; Koch 2007). Carbon isotope variations in an animal’s diet leave a geochemical fingerprint in the inorganic (e.g. carbonate in bioapatite) and organic (e.g. collagen) components of bones and teeth. Carbon isotope compositions vary among primary producers (Heaton 1999; Kohn and Cerling 2002; Koch 2007), and as such can be exploited to illuminate dietary preferences or environmental factors that alter the isotopic composition of plants (e.g. moisture level, canopy density). The resistance of enamel to post-burial geochemical alteration has made it the material of choice for stable isotope analysis (SIA) of older fossil materials (>0.05 Ma) (Wang and Cerling 1994; Kohn and Cerling 2002). However, stable isotope analysis of younger, exceptionally well-preserved bone bioapatite from some fossil and archaeological deposits (typically <0.01 Ma, but sometimes older), as well as bone bioapatite from living populations, can provide an insight into the ecology of species that might not be available from enamel bioapatite alone (Bocherens and Mariotti 1992; Lee-Thorp 2000). Unlike enamel, which is accreted over a finite interval without subsequent chemical modification following maturation, bone is remodelled throughout an animal’s life. GEOLOGICAL JOURNAL Geol. J. 44: 605–620 (2009) Published online 3 August 2009 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/gj.1173 *Correspondence to: K. Fox-Dobbs, Geology, University of Puget Sound, Tacoma, WA 98416, USA. E-mail: kena@pugetsound.edu y Authors contributed equally to the paper. Copyright # 2009 John Wiley & Sons, Ltd.