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Assessment of Indigeneity in Fossil Organic Matter: Amino Acids and Stable Isotopes [and Discussion]

Stephen A. Macko, Michael H. Engel, J. L. Bada and B. Halstead
Philosophical Transactions: Biological Sciences
Vol. 333, No. 1268, Molecules Through Time: Fossil Molecules and Biochemical Systematics (Sep. 30, 1991), pp. 367-374
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/55424
Page Count: 8
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Assessment of Indigeneity in Fossil Organic Matter: Amino Acids and Stable Isotopes [and Discussion]
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Abstract

Whereas the presence of amino acids in fossil materials is clearly related to biosynthesis, an indigenous relationship with the fossil may be suspect. At present, attempts to establish the indigeneity of amino acids in fossils are based on distribution and stereochemistry. However, fossil systems are not closed and racemization may be retarded in organic materials within a fossil matrix. The advent of new technologies has resulted in alternative methods for evaluating the authenticity of fossil organic matter. A comparison of the stable carbon isotope compositions of the D- and L-enantiomers of individual amino acids facilitates the evaluation of indigeneity. Here we report the application of this method for determining the origin(s) of amino acids in fossils and extraterrestrial samples. Further, nitrogen isotope compositions of fossil materials should reflect trophic order, with increasing enrichment in δ 15N with progression up the food chain. Establishment of the trophic position of a fossil would further reinforce the appraisal of indigeneity based on the isotopic composition of its residual organic matter. Results of initial studies on Cretaceous age vertebrates which are consistent with the suggested feeding morphologies of these organisms are also presented.

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