Tracking changing environments using stable carbon isotopes in fossil tooth enamel: an example from the South African hominin sites

Department of Archaeological Sciences, University of Bradford, BD7 1DP, UK.
Journal of Human Evolution (Impact Factor: 3.73). 12/2007; 53(5):595-601. DOI: 10.1016/j.jhevol.2006.11.020
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ABSTRACT The environmental contexts of the karstic hominin sites in South Africa have been established largely by means of faunal associations; taken together these data suggest a trend from relatively closed and more mesic to open, drier environments from about 3 to 1.5 Ma. Vrba argued for a major shift within this trend ca. 2.4-2.6 Ma, an influential proposal that posited links between bovid (and hominin) radiation in Africa and the intensification of Northern Hemisphere Glaciation. Yet faunal approaches often rely on habitat and feeding preferences of modern taxa that may differ from those of their extinct predecessors. Here we explore ways of extending (13)C/(12)C data from fossil mammals beyond denoting "presence" or "absence" of C(4) grasses using the evolution of open environments in South Africa as a case study. To do so we calculated the relative proportions of C(3)-, mixed-, and C(4)-feeding herbivores for all the hominin sites for which we have sufficient data based on (13)C/(12)C analyses of fossil tooth enamel. The results confirm a general trend towards more open environments since 3 Ma, but they also emphasize a marked change to open grassy habitats in the latest Pliocene/early Pleistocene. Mean (13)C/(12)C for large felids also mirrored this trend.

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Available from: Matt Sponheimer, Sep 28, 2015
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    • "These changes manifest terrestrially as an expansion of C 4 grasses predominantly in regions experiencing a reduction in rainfall (Ehleringer et al., 1991, 1997; Hopley et al., 2007a). Analysis of biomineral carbonate δ 13 C demonstrates the presence of C 4 vegetation the early Pliocene (Ségalen et al., 2006) with the most significant environmental change to open, grassy landscapes only occurring after 2 Ma when arid conditions became dominant (Hopley et al., 2007a; Lee-Thorp et al., 2007). The Plio- Pleistocene Thabaseek Tufa δ 18 O data (− 6.5‰ to − 5.7‰; mean = −6.0‰; "
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    ABSTRACT: The tufa deposits of the Ghaap Plateau escarpment provide a rich, yet minimally explored, geological archive of climate and environmental history coincident with hominin evolution in South Africa. This study examines the sedimentary and geochemical records of ancient and modern tufas from Buxton-Norlim Limeworks, Groot Kloof, and Gorrokop, to assess the potential of these sediments for providing reliable chronologies of high-resolution, paleoenvironmental information. Chronometric dating demonstrates that tufa formation has occurred from at least the terminal Pliocene through to the modern day. The stable isotope records show a trend toward higher, more variable δ18O and δ13C values with decreasing age from the end of the Pliocene onwards. The long-term increase in δ18O values corresponds to increasingly arid conditions, while increasing δ13C values reflect the changing proportion of C3/C4 vegetation in the local environment. Analysis of the Thabaseek Tufa, in particular, provides valuable evidence for reconstructing the depositional and chronological context of the enigmatic Taung Child (Australopithecus africanus). Collectively, the results of the present study demonstrate the potential of these deposits for developing high-precision records of climate change and, ultimately, for understanding the causal processes relating climate and hominin evolution.
    Quaternary Research 05/2015; 84(1). DOI:10.1016/j.yqres.2015.04.008 · 2.54 Impact Factor
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    • "The Unit C Acheulean deposits were accumulated by carnivores , with an additional component of hillwash that was responsible for bringing artifacts into the cave. All the carnivore specimens that have been analyzed for stable isotope analysis are listed as Member 5 (Luyt 2001; Lee-Thorp et al. 2007), without subdivision into Unit B or Unit C. Therefore of the four faunal assemblages investigated in our study, only Sterkfontein Member 5 can be assumed to be a temporally mixed assemblage on the basis of prior stratigraphic information. Swartkrans Member 1, Hanging Remnant.— "
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    ABSTRACT: Fundamental to the interpretation of bone-bearing faunal deposits is an understanding of the taphonomic processes that have modified the once living fossil community. An often neglected source of bias is that of climate-averaging, which occurs when the duration of bone accumulation exceeds the duration of an individual climatic episode. Tropical and subtropical climate change is dominated by precessional cyclicity (∼21,000 year cycle), which controls monsoon rainfall intensity and thus plant communities over time. Under a climate-averaging scenario, the paleoecological characteristics of a faunal deposit represent an amalgamation of more than one phase of the precessional cycle. We investigate the degree of climate-averaging in Plio-Pleistocene bone breccias from South Africa by comparing stable isotope measurements of fossil enamel with the evidence from high-resolution speleothem paleoclimate proxies. We conclude that each of the four faunal assemblages studied are climate-averaged, having formed over a time period in excess of one-third of a precessional cycle (∼7000 years). This has implications for the reconstruction of hominin paleoenvironments and estimates of Plio-Pleistocene biodiversity. We hypothesize that climate-averaging may be a common feature of tropical terrestrial vertebrate assemblages throughout the Cenozoic and Mesozoic.
    Paleobiology 12/2010; 36(1):32-50. DOI:10.1666/0094-8373-36.1.32 · 2.66 Impact Factor
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    • "The Pliocene development of the boundary conditions controlling these climatic conditions (e.g. Marlow et al., 2000; Udeze & Oboh-Ikuenobe, 2005) is coincident with significant changes in East Africa (Hernández Fernández & Vrba, 2006) and eastern South Africa (Vrba, 1985; Lee-Thorp et al., 2007) that mark the development of drier conditions and the continued expansion of C 4 grasslands that followed the closing of the Panama seaway and the intensification of the Northern Hemisphere glaciation (Lear et al., 2003; deMenocal, 2004). Together, these dramatic changes in global and regional climates and controls are considered to be likely mechanisms for the fragmentation of closed habitats and the radiation of chameleon lineages through the Pliocene. "
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    ABSTRACT: Aim  The high amount of species diversity concentrated in southern Africa has been attributed to palaeoclimatic factors, and the timing of radiations in some taxa corresponds to global palaeoclimatic trends. Using dwarf chameleons (Bradypodion: Chamaeleonidae) as a model system, we explored the relationship between palaeoclimatic fluctuations and cladogenesis with respect to both temporal and spatial patterns in an effort to understand the process of speciation in southern Africa.Location  South Africa, with particular emphasis on the Cape Floristic Region and the Maputaland–Pondoland–Albany hotspot.Methods  Mitochondrial sequence data (ND2 and 16S) were used to estimate the timing of major radiations and to examine the number of lineages through time. A dated phylogeny was constructed using Bayesian phylogenetic reconstruction, and a Bayesian relaxed molecular clock was used to estimate divergence times. Spatial data and lineage-through-time plots were used to identify geographic regions that underwent diversification in connection with major climatic events. Both parsimony and likelihood optimizations of habitat type on the phylogeny were used to determine whether major habitat shifts have occurred. On a coarse scale (half-degree grid cells), phylogenetic diversity (sum of the branch lengths linking terminals) was compared with species richness (absolute number of species) to identify areas of conservation importance.Results  The complete species phylogeny of dwarf chameleons shows that the timing and mode of diversification exhibit spatio-temporal patterns that link to phases in the evolution of southern Africa’s climate over the last 14 Myr. Optimizations of habitat on the phylogenetic tree show a progression from closed to open habitats since the Mid-Miocene, corresponding to the shift from C3 to C4 environments, and later with the development of south-western Africa’s winter-rainfall regime. These shifts are not simultaneous across the region, with different geographic centres of diversity generated during different time periods.Main conclusions  Regions that are prominent centres of chameleon diversification are encompassed by the current biodiversity hotspots as shown by chameleon species richness and phylogenetic diversity. Diversity within the Cape Floristic Region appears to be the result of a Late Pliocene radiation, whereas the diversity encompassed within the Maputaland–Pondoland–Albany hotspot is an aggregate of asynchronous radiation events, probably influenced by lineage losses. Overall, dwarf chameleons have experienced a shift in habitat types, with recent radiations occupying open habitats, and older lineages persisting in relictual forested habitats, corresponding to the continental shift of vegetation types since the Miocene Climatic Optimum.
    Journal of Biogeography 07/2008; 35(8):1402 - 1414. DOI:10.1111/j.1365-2699.2008.01889.x · 4.59 Impact Factor
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