54-9 Carbon isotopes of enamel-bound organic matter through grassland expansion in Bolivia – a new paleobiological archive

Session: New Approaches to Old Fossil Collections

Presenting Author:

Mason Scher

Authors:

Scher, Mason¹, Kast, Emma², Rinaldi, Nicole³, Rao, Crystal⁴, Auderset, Alexandra⁵, Cadeau, Pierre⁶, Oleynik, Sergey⁷, Sigman, Daniel⁸

(1) Department of Geosciences, Princeton University, Princeton, NJ, USA, (2) Department of Geosciences, Princeton University, Princeton, NJ, USA, (3) Department of Geosciences, Princeton University, Princeton, NJ, USA, (4) Department of Geosciences, Princeton University, Princeton, NJ, USA, (5) School of Ocean and Earth Science, University of Southampton, Southampton, United Kingdom, (6) Geo-Ocean, IFREMER, Plouzané, France, (7) Department of Geosciences, Princeton University, Princeton, NJ, USA, (8) Department of Geosciences, Princeton University, Princeton, NJ, USA,

Abstract:

The δ¹³C of structural carbonate within tooth enamel (δ¹³C_CO3) serves as a proxy for average dietary C and is often applied to the fossil record. One of the earlier applications of δ¹³C_CO3 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 δ¹³C_CO3, studies of modern animals have shown the ¹³C enrichment of δ¹³C_CO3 varies from ~9-16‰. Measurements of organic matter δ¹³C give a more direct measure of δ¹³C_diet, 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 δ¹³C_EBOM measurements from the same sample set used by MacFadden et al. (1994) for δ¹³C_CO3. ∆δ¹³C_CO3-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 δ¹³C_EBOM for (1) validating δ¹³C_CO3 records, and (2) combining with δ¹³C_CO3 records to improve our understanding of fossil animal biology and physiology.  

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11045

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