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      Isotopic evidence for an early shift to C₄ resources by Pliocene hominins in Chad.

      Proceedings of the National Academy of Sciences of the United States of America

      Animals, Archaeology, Carbon Isotopes, analysis, Chad, Dental Enamel, chemistry, Diet, Ecosystem, Fossils, History, Ancient, Hominidae, physiology, Plants, Edible

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          Abstract

          Foods derived from C(4) plants were important in the dietary ecology of early Pleistocene hominins in southern and eastern Africa, but the origins and geographic variability of this relationship remain unknown. Carbon isotope data show that Australopithecus bahrelghazali individuals from Koro Toro in Chad are significantly enriched in (13)C, indicating a dependence on C(4) resources. As these sites are over 3 million years in age, the results extend the pattern of C(4) dependence seen in Paranthropus boisei in East Africa by more than 1.5 million years. The Koro Toro hominin fossils were found in argillaceous sandstone levels along with abundant grazing and aquatic faunal elements that, in combination, indicate the presence of open to wooded grasslands and stream channels associated with a greatly enlarged Lake Chad. In such an environment, the most abundant C(4) plant resources available to A. bahrelghazali were grasses and sedges, neither of which is usually considered as standard great ape fare. The results suggest an early and fundamental shift in hominin dietary ecology that facilitated the exploitation of new habitats.

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          Most cited references 35

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          The evolution of C4photosynthesis

           Rowan Sage (2004)
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            The isotopic ecology of East African mammals.

            The stable carbon and nitrogen isotope ratios of bone collagen have been used to trace diet and habitat selection of the larger mammals of East Africa. 238 individuals of 43 species from montane forests and grasslands in Kenya and Tanzania have been analyzed. The results show that carbon isotopes discriminate between (1) grazers and browsers in savanna grasslands, (2) forest floor and savanna grassland herbivores and (3) forest floor and forest canopy species. Nitrogen isotopes discriminate between (4) carnivores and herbivores, (5) forest and savanna grassland herbivores, and (6) water-dependent and drought-tolerant herbivores. This technique provides a quantitative approach to assessing long-term habitat and diet selection and the role of resource partitioning in animal community structure.
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              Early hominid evolution and ecological change through the African Plio-Pleistocene.

               K. Reed (2015)
              The habitats in which extinct hominids existed has been a key issue in addressing the origin and extinction of early hominids, as well as in understanding various morphological and behavioral adaptations. Many researchers postulated that early hominids lived in an open savanna (Dart, 1925; Robinson, 1963; Howell, 1978). However, Vrba (1985, 1988) has noted that a major global climatic and environmental shift from mesic, closed to xeric, open habitats occurred in the late African Pliocene (approximately 2.5 m.y.a.), thus implying that the earliest hominids existed in these mesic, wooded environs. This climatic shift is also suggested to have contributed to a pulse in speciation events with turnovers of many bovid and possibly hominid species. Previous environmental reconstructions of hominid localities have concentrated on taxonomic identities and taxonomic uniformitarianism to provide habitat reconstructions (e.g., Vrba, 1975; Shipman & Harris, 1988). In addition, relative abundances of species are often used to reconstruct a particular environment, when in fact taphonomic factors could be affecting the proportions of taxa. This study uses the morphological adaptations of mammalian assemblages found with early hominids to reconstruct the habitat based on each species' ecological adaptations, thus minimizing problems introduced by taxonomy and taphonomy. Research presented here compares east and south African Plio-Pleistocene mammalian fossil assemblages with 31 extant mammalian communities from eight different habitat types. All communities are analyzed through ecological diversity methods, that is, each species trophic and locomotor adaptations are used to reconstruct an ecological community and derive its vegetative habitat. Reconstructed habitats show that Australopithecus species existed in fairly wooded, well-watered regions. Paranthropus species lived in similar environs and also in more open regions, but always in habitats that include wetlands. Homo is the first hominid to exist in areas of fairly open, arid grassland. This change from closed to open habitats occurs gradually from about 4 m.y.a. until about 2 m.y.a. when there is a major increase in arid and grazing adapted mammals. Therefore, the appearance of open savannas do not appear to have influenced the origination or adaptations of the earliest hominids, but could have contributed to their demise. As Stanley (1992) hypothesized, Homo species appear the first to be adapted to open, arid environments.
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                Author and article information

                Journal
                23150583
                3528505
                10.1073/pnas.1204209109

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