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| Titel |
Stable isotope time series and dentin increments elucidate Pleistocene proboscidean paleobiology |
| VerfasserIn |
Daniel Fisher, Adam Rountrey, Kathlyn Smith, David Fox |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250037804
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| Zusammenfassung |
| Investigations of stable isotope composition of mineralized tissues have added greatly to our
knowledge of past climates and dietary behaviors of organisms, even when they are
implemented through “bulk sampling”, in which a single assay yields a single, time-averaged
value. Likewise, the practice of “sclerochronology”, which documents periodic structural
increments comprising a growth record for accretionary tissues, offers insights into rates of
growth and age data at a scale of temporal resolution permitted by the nature of structural
increments. We combine both of these approaches to analyze dental tissues of late Pleistocene
proboscideans. Tusk dentin typically preserves a record of accretionary growth consisting of
histologically distinct increments on daily, approximately weekly, and yearly time scales.
Working on polished transverse or longitudinal sections, we mill out a succession of
temporally controlled dentin samples bounded by clear structural increments with a
known position in the sequence of tusk growth. We further subject each sample
(or an aliquot thereof) to multiple compositional analyses – most frequently to
assess δ18O and δ13C of hydroxyapatite carbonate, and δ13C and δ15N of collagen.
This yields, for each animal and each series of years investigated, a set of parallel
compositional time series with a temporal resolution of 1-2 months (or finer if we
need additional precision). Patterns in variation of thickness of periodic sub-annual
increments yield insight into intra-annual and inter-annual variation of tusk growth rate.
This is informative even by itself, but it is still more valuable when coupled with
compositional time series. Further, the controls on different stable isotope systems are
sufficiently different that the data ensemble yields “much more than the sum of its
parts.” By assessing how compositions and growth rates covary, we monitor with
greater confidence changes in local climate, diet, behavior, and health status. We
illustrate the potential of this approach with case studies that reveal: season of birth
and age of weaning in juvenile mammoths; age of maturation in male mastodons;
season of musth in mammoths and mastodons; and season of death and tests of
simultaneity of death in mammoths and mastodons. The data provided by histological
and stable isotope analyses rarely reveal cause of death directly, but they can, in
concert with other observations, affect perceptions of the likelihood of competing
interpretations of cause of death. Most important, paleobiological inferences based on
these studies can be integrated over broad geographic and temporal scales to show
how specific paleobiological traits changed through time, prior to extinction. These
studies have great power for investigating causes of extinction because contrasting
patterns of change are expected under different hypothesized drivers of extinction. |
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