54 New Approaches to Old Fossil Collections

Material collected during the early history of paleontology conserves deep time ecosystems and remains available for study. We invite presentations of new analyses and interpretations of well-studied collections in the context of the broader history of the discipline.

Sunday, 19 October 2025
1:30 PM - 5:30 PM
HBGCC, 303AB

Carbon isotopes of enamel-bound organic matter through grassland expansion in Bolivia – a new paleobiological archive

Paper number: 54-10
Program: Technical Sessions
Time: 3:55 PM – 4:15 PM

Authors

Abstract

The δ13C of structural carbonate within tooth enamel (δ13CCO3) serves as a proxy for average dietary C and is often applied to the fossil record. One of the earlier applications of δ13CCO3 was by MacFadden et al. (1994) using a record of fossil megaherbivore teeth from several sites in Bolivia, showing C4 grasses were a significant portion of herbivore diets by ~ 10 Ma. Though a 14‰ offset is often applied to calculate diet δ13C from δ13CCO3, studies of modern animals have shown the 13C enrichment of δ13CCO3 varies from ~9-16‰. Measurements of organic matter δ13C give a more direct measure of δ13Cdiet, but the application to the fossil record is limited as even bone and dentin collagen degrade rapidly (10-100 kA timescale).

 

Primary organics are preserved on million-year timescales in tooth enamel, though their low concentrations have traditionally precluded isotopic analysis. In this work, we present the first measurements of enamel-bound organic matter (EBOM) δ13C measured on a modified EA-IRMS system capable of analyzing ~100 nmol C, requiring ~8 mg of enamel, providing an organic δ13C record from animals in deep time. We present δ13CEBOM measurements from the same sample set used by MacFadden et al. (1994) for δ13CCO3. ∆δ13CCO3-EBOM ranges from ~11 to 17‰ and clusters by animal group, revealing additional paleobiological information potentially related to body size and/or digestive physiology, and refining estimates of C3/4 feeding. We propose the use of δ13CEBOM for (1) validating δ13CCO3 records, and (2) combining with δ13CCO3 records to improve our understanding of fossil animal biology and physiology.  

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-414773

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