TY - JOUR
T1 - Stable isotope time-series in mammalian teeth
T2 - In situ δ18O from the innermost enamel layer
AU - Blumenthal, Scott A.
AU - Cerling, Thure E.
AU - Chritz, Kendra L.
AU - Bromage, Timothy G.
AU - Kozdon, Reinhard
AU - Valley, John W.
N1 - Funding Information:
We thank B.H. Passey for providing samples and data, Brian Hess and Quintin Sahratian for assistance with sample preparation, and Matt DeLong for assistance with imaging. We thank Paul Tafforeau, Fred J. Longstaffe, and an anonymous reviewer for providing suggestions and comments. This research was funded by the New York Consortium of Evolutionary Primatology NSF DGE 0333415, NSF BCS 0621542, and Sigma Xi G20110315157181. Research support was also provided by the 2010 Max Planck Research Award to TGB, endowed by the German Federal Ministry of Education and Research to the Max Planck Society and the Alexander von Humboldt Foundation in respect of the Hard Tissue Research Program in Human Paleobiomics. WiscSIMS is partly supported by NSF (EAR03-19230, EAR10-53466).
PY - 2014/1/1
Y1 - 2014/1/1
N2 - Stable carbon and oxygen isotope ratios in mammalian tooth enamel are commonly used to understand the diets and environments of modern and fossil animals. Isotope variation during the period of enamel formation can be recovered by intra-tooth microsampling along the direction of growth. However, conventional sampling of the enamel surface provides highly time-averaged records in part due to amelogenesis. We use backscattered electron imaging in the scanning electron microscope (BSE-SEM) to evaluate enamel mineralization in developing teeth from one rodent and two ungulates. Gray levels from BSE-SEM images suggest that the innermost enamel layer, <20μm from the enamel-dentine junction, is highly mineralized early in enamel maturation and therefore may record a less attenuated isotopic signal than other layers. We sampled the right maxillary incisor from a woodrat subjected to an experimentally induced water-switch during the period of tooth development, and demonstrate that secondary ion mass spectrometry (SIMS) can be used to obtain δ18O values with 4-5-μm spots from mammalian tooth enamel. We also demonstrate that SIMS can be used to discretely sample the innermost enamel layer, which is too narrow for conventional microdrilling or laser ablation. An abrupt δ18O switch of 16.0% was captured in breath CO2, a proxy for body water, while a laser ablation enamel surface intra-tooth profile of the left incisor captured a δ18O range of 12.1%. The innermost enamel profile captured a δ18O range of 15.7%, which approaches the full magnitude of δ18O variation in the input signal. This approach will likely be most beneficial in taxa such as large mammalian herbivores, whose teeth are characterized by less rapid mineralization and therefore greater attenuation of the enamel isotope signal.
AB - Stable carbon and oxygen isotope ratios in mammalian tooth enamel are commonly used to understand the diets and environments of modern and fossil animals. Isotope variation during the period of enamel formation can be recovered by intra-tooth microsampling along the direction of growth. However, conventional sampling of the enamel surface provides highly time-averaged records in part due to amelogenesis. We use backscattered electron imaging in the scanning electron microscope (BSE-SEM) to evaluate enamel mineralization in developing teeth from one rodent and two ungulates. Gray levels from BSE-SEM images suggest that the innermost enamel layer, <20μm from the enamel-dentine junction, is highly mineralized early in enamel maturation and therefore may record a less attenuated isotopic signal than other layers. We sampled the right maxillary incisor from a woodrat subjected to an experimentally induced water-switch during the period of tooth development, and demonstrate that secondary ion mass spectrometry (SIMS) can be used to obtain δ18O values with 4-5-μm spots from mammalian tooth enamel. We also demonstrate that SIMS can be used to discretely sample the innermost enamel layer, which is too narrow for conventional microdrilling or laser ablation. An abrupt δ18O switch of 16.0% was captured in breath CO2, a proxy for body water, while a laser ablation enamel surface intra-tooth profile of the left incisor captured a δ18O range of 12.1%. The innermost enamel profile captured a δ18O range of 15.7%, which approaches the full magnitude of δ18O variation in the input signal. This approach will likely be most beneficial in taxa such as large mammalian herbivores, whose teeth are characterized by less rapid mineralization and therefore greater attenuation of the enamel isotope signal.
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U2 - 10.1016/j.gca.2013.09.032
DO - 10.1016/j.gca.2013.09.032
M3 - Article
AN - SCOPUS:84887005978
SN - 0016-7037
VL - 124
SP - 223
EP - 236
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -