Paleoecological patterns at the Hadar hominin site, Afar Regional State, Ethiopia.
ABSTRACT Reconstructing paleoecological patterns associated with hominin taxa, such as Australopithecus afarensis, is important for understanding possible evolutionary mechanisms involved in extinction and speciation events. It is critical to identify local, regional, or pan-African causal factors because patterns at these different levels may affect separate populations of the same species of hominin in unique ways. Habitat reconstructions of 12 submembers of the Hadar and Busidima formations (approximately 3.8-2.35 Ma) are presented here along with faunal differences in these submembers through time. Habitats with medium density tree and bush cover dominated the landscape through much of the earlier time period in the Hadar Formation. The lowermost Sidi Hakoma Member is the most closed habitat. The Denen Dora Member shows the influence of frequent floodplain edaphic grasslands with high abundances of reducin bovids. There is an influx of ungulates in the Kada Hadar Member (approximately 3.2--approximately 2.96 Ma) that indicates a more arid habitat populated by mammals that were recovered from earlier deposits further south in Ethiopia and Kenya. In the younger deposits from the Busidima Formation at Hadar, the landscape was open wooded grassland with some floodplain environments. The fossil assemblages from the Busidima Formation show a substantial species turnover. Although high numbers of A. afarensis specimens are associated with the lower Sidi Hakoma Member, they clearly inhabited a variety of habitats throughout the entire Hadar Formation. Australopithecus afarensis from Laetoli through Hadar times appears to have been a eurytopic species.
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ABSTRACT: Sedimentary basins in eastern Africa preserve a record of continental rifting and contain important fossil assemblages for interpreting hominin evolution. However, the record of hominin evolution between 3 and 2.5 million years ago (Ma) is poorly documented in surface outcrops, particularly in Afar, Ethiopia. Here we present the discovery of 2.84-2.58 Ma fossil and hominin-bearing sediments in the Ledi-Geraru research area that have produced the earliest record of the genus Homo. Vertebrate fossils record a faunal turnover indicative of more open and probable arid habitats than those reconstructed earlier in this region, in broad agreement with hypotheses addressing the role of environmental forcing in hominin evolution at this time. Geological analyses constrain depositional and structural models of the Afar and date the LD 350-1 Homo mandible to 2.80-2.75 Ma. Copyright © 2015, American Association for the Advancement of Science.Science 03/2015; 347(6228):1355-1359. DOI:10.1126/science.aaa1415 · 31.48 Impact Factor
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ABSTRACT: Eastern and southern Africa experienced ongoing climatic and tectonic instability in the Plio-Pleistocene, alongside declining forests and expanding grasslands. Most known hominin genera (Australopithecus spp., Kenyanthropus, Paranthropus spp., Homo spp.) appear roughly between 4.2 and 1.8 Ma (millions of years ago). Explanations for these speciation events have focused on adaptations to environmental change, particularly in terrestrial biomes. However, the links between environmental change and hominin adaptations have not always been clear. Often overlooked is that Plio-Pleistocene vegetation included not just terrestrial environments, but a large component of edaphic (wet) C4 grasses and sedges. In this paper it is suggested that in response to environmental fluctuations, hominins engaged in conservative long-term ecological and dietary patterns, based on predictable C4/C3 wetland and terrestrial resources. Data are presented from six hominin locales, which demonstrate reliance on plant-based resources (sedges, grasses, and other vegetation) in C4-inclusive wetland/savanna mosaics. After roughly 2.4 Ma, severe climate variability is associated with early Homo and perhaps Paranthropus boisei broadening their diet to familiar but less preferred foods: vertebrates and invertebrates. These foods consistently provided early Homo with essential nutrients, which reduced selection pressures and allowed for increases in brain size. After 1.65 Ma, a 20% increase in the C4 dietary component of Homo occurs alongside increased relative brain size. P. boisei also increases its C4 dietary component by 15% after 1.65 Ma. These increases imply that both taxa continued to broaden their diet within the C4-based wetlands/savanna biome, with Homo putting a greater emphasis on mammals.Journal of Human Evolution 11/2014; 77. DOI:10.1016/j.jhevol.2014.10.003 · 3.87 Impact Factor
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ABSTRACT: The Upper Laetolil Beds of Laetoli, Tanzania (∼3.6–3.85 Ma) has yielded a large and varied faunal assemblage, including specimens of Australopithecus afarensis. In contrast with contemporaneous eastern African A. afarensis sites in Kenya and Ethiopia, there is no indication of permanent rivers or other large bodies of water at the site, and the apparently drier environment supported a quite different faunal and floral community as reconstructed from the fossil record. Therefore, a deeper understanding of the paleoecology at Laetoli can be illuminating for questions of habitat access and use by A. afarensis, as well as its behavioral flexibility. This paper reviews the substantial body of evidence accumulated that allows for a detailed reconstruction of the Pliocene paleoenvironment of Laetoli. A synthesis of the different lines of evidence suggests that the Upper Laetolil Beds was a mosaic of grassland–shrubland–woodland habitats with extensive woody vegetation in the form of shrubs, thickets and bush, as well as a significant presence of dense woodland habitats along seasonal river courses and around permanent springs. The vegetation during the Pliocene at Laetoli was likely impacted by the strongly seasonal availability of water and the volcanic ash falls that periodically blanketed the area. A comparison with the paleoenvironments of other A. afarensis sites and a review of its inferred dietary behavior suggest that A. afarensis was an ecological generalist that was able to consume a wide variety of dietary resources in mosaic habitats, although their differential abundances at different sites may be indicative of specific ecological requirements that impact their success in particular environments.Journal of African Earth Sciences 10/2014; DOI:10.1016/j.jafrearsci.2014.09.019 · 1.38 Impact Factor