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| Titel |
Non-traditional isotope analysis of fossil bones and teeth - Preservation of biogenic compositions or diagenetic alteration? |
| VerfasserIn |
Thomas Tütken, Robert A. Eagle, Alexander Heuser, Daniel Herwartz, Stephen J. G. Galer |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250056137
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| Zusammenfassung |
| Bones and teeth are valuable geochemical archives of the life history and behaviour, as well
as the habitat of extant and extinct vertebrates. The isotope compositions of the skeletal
bioapatite records information about the animals diet, (thermo-)physiology and mobility as
well as climate and environmental conditions. Isotope analysis of bones and teeth is
thus increasingly used in ecological, forensic, anthropological, archaeological and
palaeontological studies.
Besides traditional isotope systems (δ18O, δ13C, δ15N, δ34S, 87Sr/86Sr), non-traditional
isotope systems such as δ44Ca and Δ47 can yield additional information about the diet and
thermophysiology of extinct vertebrates, respectively. Before investigating extinct vertebrates
and ancient ecosystems, it is important to calibrate these new non-traditional isotope proxies
on living vertebrates and well-characterized present-day ecosystems. Furthermore, it is
crucial to understand the preservation of these chemical proxies in fossil skeletal
remains. Studies in both these areas are currently underway and first results will be
discussed.
Calcium isotopes (δ44Ca) in bones and teeth of living animals can yield information
about their diet, and about the trophic level of these organisms within the local food chain.
Calcium is the major element in bioapatite and, based upon current understanding, no
significant alteration of biogenic appears to take place during diagenesis. Thus, δ44Ca values
provide a promising new proxy with high preservation potential for reconstructing
diet of extinct vertebrates and for delimiting ancient food webs. The Ca isotope
fractionation that occurs between diet and skeletal apatite remains comparatively poorly
understood, however, and further work in this area is needed. Additionally, the Ca
isotope compositions of living species with more varied dietary intake must be
characterized to exploit fully the potential of Ca isotopes in evaluating diet of extinct
taxa.
Clumped isotope (Δ47) analysis of the 13C-18Oexcess in carbonate-containing enamel
bioapatite of living vertebrates with different, known body temperatures yielded an
Δ47-temperature calibration that allows determining vertebrate body temperatures with an
accuracy of 1-2Ë C (Eagle et al., 2010). Enamel Δ47 values can be preserved over millions of
years, in principle, as Δ47 analyses of fossil teeth from Pleistocene mammoths as well as a
Late Miocene rhinoceros and alligator imply body temperatures within error of those for
modern taxa (Eagle et al., 2010). Clumped isotope thermometry is establishing itself as a
promising new chemical thermometer for examining the thermophysiology of extinct
vertebrates, such as dinosaurs. A note of caution is warranted, however, as the effects of
diagenesis on Δ47 are not yet fully understood, and will need to be investigated in detail
if this new and important tool is to fulfill its intial promise. In the meantime, a
multi-proxy approach combining histological (transmitted light microscopy, μ-CT),
mineralogical (XRD, EMPA) and chemical (δ13C, δ18O, rare earth elements) indicators is
recommended to characterize the enamel preservation and screen for diagenetic
overprinting.
Rare earth elements (REE) are valuable chemical tracers for inferring the diagenetic
conditions, as well as the time and place of fossilisation. Both intra-bone REE concentration
profiles and unsuccessful attempts at radiometric Lu-Hf dating of bone provide clear evidence
that fossil bones (and even teeth) behave as open systems with respect to REE and Hf over
geological timescales of millions of years (Herwartz et al., 2011), rather than thousands of
years, as previously been suggested.
Regrettably, the possibility of directly and reliably dating of fossil bone by Lu-Hf
methods appears remote based upon current research and case studies. However, for materials
that are relatively unaltered during fossilization, non-traditional isotope systems, such as
δ44Ca and Δ47, are expected to contribute significantly to our understanding of the
palaeo-diet and physiology of extinct vertebrates, and thus help to unravel some
mysteries in palaeontology not amenable to study by long-established traditional
means.
References:
Eagle, R.A., Schauble, E.A., Tripati, A.K., Tütken, T., Hulbert, R.C. & Eiler, J.M.
(2010) Body temperatures of modern and extinct vertebrates from 13C-18O bond
abundances in bioapatite. Proceedings of the National Academy of Sciences 107,
10377-10382.
Herwartz, D., Tütken, T., Münker, C., Jochum, K.-P., Stoll, B. & Sander, M. (2011)
Timescales and mechanisms of REE and Hf uptake in fossil bones. Geochimica et
Cosmochimica Acta 75, 82-105. |
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