Paleoecological reconstructions in southern Egypt based on the stable carbon and nitrogen isotopes in the organic fraction and stable carbon isotopes in individual amino acids of fossil ostrich eggshell

Abstract

Previous studies on ostrich eggshell (OES) have demonstrated the remarkable integrity of this medium for the retention of indigenous proteinaceous residues over 106 yr and more (e.g., Brooks et al., 1990; Miller et al., 1992). Such integrity suggests that the initial isotopic composition of the organic molecules might also be retained, and the stable isotopes of carbon (~ t 3 C ) and nitrogen (~ 15N ) in various organic fractions, including fil3C in individual amino acids, might be used to provide some information about the ecology at the time the egg was formed. Carbon isotopes in the organic and inorganic fractions of bones and teeth from herbivores are reasonably well-established indices of the relative proportions of C3 and Ca plants consumed (e.g., van der Merwe, 1982; DeNiro, 1987; van der Merwe et al., 1988). C3 plants (mean ~13C=-26.5+_2%o; O'Leary, 1981) include all trees and most shrubs and grasses adapted to temperate or shaded tropical forests. Ca plants (mean ~ 3 C = 12.5+ lO/oo; O'Leary, 1981 ) include most tropical grasses and a few shrubs adapted to high temperatures and radiation. Based on these observations, general paleoecological interpretations can often be made from the