Stable Isotope Compositions of Biological Apatite

Abstract

The stable isotope compositions of biogenic materials record a combination of environmental parameters and biological processes. In general, the environment provides a range of isotopic compositional inputs, and an animal processes those signals through dietary preference, physiology, behavior, etc. Geochemists then use isotope signals preserved in biogenic materials to infer either what the biologic filter was (i.e., a species-specific biologic process), or the environment in which the animal lived (e.g., see review of Koch 1998). Although stable isotopes of hydrogen, carbon, nitrogen, oxygen, and strontium in modern-day animals have provided fruitful information on environment or biology, preservation of hydrogen and nitrogen is poor for most fossil materials, especially those older than a few million years. Consequently, nearly all stable isotope studies focus on the best preserved tissues, which are biological apatites (or bioapatites)— bone, dentin, enamel, scales, etc.—and on the most diagenetically resistant isotopes–oxygen, carbon, and occasionally strontium, which occur as principal or substitutional components in bioapatite. Because of the inherent synergy between biology and environment, the scientific scope of stable isotope research on bioapatites is quite broad. In addition to studies of terrestrial paleoclimate and dietary preference, stable isotopes in bioapatite have helped elucidate such diverse issues as dinosaur thermoregulation (Barrick and Showers 1994, 1995; Barrick et al. 1996, 1998; Fricke and Rogers 2000), the global rise of C4 plants (Cerling et al. 1993, 1997), pinniped migration (Burton and Koch 1999), cetacean osmoregulation (Thewissen et al. 1996, Roe et al. 1998), herding practices (Bocherens et al. 2001), topographic uplift (Dettman et al. 2001, Kohn et al. 2003), the demise of Norse colonies in Greenland (Fricke et al. 1995, Arneborg et al. 1999), Miocene “rhinoceros” ecology (MacFadden 1998), and mastodon migration (Hoppe et al., 1999)! In this chapter, we first describe …