Opportunities and constraints for reconstructing palaeoenvironments from stable light isotope ratios in fossils

Abstract

Stable light isotope ratios (13 C/12 Cand 18 O/16 O) in fossil teeth provide key archives for understanding ecology of past faunal communities and the evolution of environments during the Plio-Pleistocene. Given the inevitable processes of diagenesis during fossilisation, the integrity of isotopic information and the degree of detailed information that can be extracted, remain important issues in all fossil studies. The most appropriate tests are those intrinsic to isotopic abundances in ecosystems. They are easier to develop for 13 C/12 C in savanna environments where large 13 C/12 C differences exist between C4 tropical grasses and C3 trees and shrubs. Validating 18 O/16 O ratios in fossil carbonate or phosphate is more difficult, but patterned variability, mainly tracking water-related behaviour, within modern faunal communities has been replicated in several fossil assemblages. The identification of seasonal variation in 13 C/12 C and 18 O/16 O along the growth axis of a tooth crown, also applicable in areas composed solely of C3 plants, fills a dual role as a test and for providing data on seasonal amplitude. The results of studies from low- and mid-latitude African sites suggest that isotopic variation in rainfall on short timescales and ecological differences amongst animals, dominate over smaller differences in 18 O/16 O composition due to temperature.