A new hominin from the Basal Member of the Hadar Formation, Dikika, Ethiopia, and its geological context. Journal of Human Evolution, 49, 499-514

Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D-04103 Leipzig, Germany.
Journal of Human Evolution (Impact Factor: 3.73). 11/2005; 49(4):499-514. DOI: 10.1016/j.jhevol.2005.06.001
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In this paper we report for the first time hominin remains from the Basal Member of the Hadar Formation at Dikika, in the Awash Valley of Ethiopia, dating to greater than 3.4 Ma. The new fossil, DIK-2-1, is a fragment of a left mandible and associated dentition. The mandible is attributed to Australopithecus afarensis. However, the new fossil exhibits some metric and morphological features that have not previously been seen in the A. afarensis hypodigm, increasing the already impressive degree of variation in the mandibular sample of the species.

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    • "Therefore, attribution of A. bahrelghazali to A. afarensis sensu lato, i.e., the 3.4e3.0 Ma old specimens from Hadar (Johanson et al., 1982) and the >3.4 Ma material from Dikika (Alemseged et al., 2005, 2006), is not supported, whilst attribution to A. afarensis sensu stricto, i.e., hominins from Laetoli, remains questionable. An early dispersal date for A. bahrelghazali is not only implicated on geological and morphological grounds however, but seems probable when palaeoclimatic evidence is considered. "
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    ABSTRACT: Australopithecus bahrelghazali, its origin and palaeobiology are not well understood. Reported from only one location some several thousand kilometres away from East African Pliocene hominin sites, it appears to have predominantly fed on C4 sources. Yet, it lacks the morphological adaptations of other primate C4 consumers like Paranthropus boisei and Theropithecus oswaldi. Furthermore, although considered to belong to Australopithecus afarensis by most researchers, A. bahrelghazali appears to differ from the former in a key aspect of its morphology: enamel thickness. To assess the phylogeny and palaeobiology of A. bahrelghazali, I first evaluate the dietary adaptations and energetics of A. bahrelghazali using empirical data of the feeding ecology of extant baboons, Papio cynocephalus. Information published on A. bahrelghazali morphology and habitat preference is used to select C4 foods with the appropriate mechanical properties and availability within the environment to create the models. By altering the feeding time on various food categories, I then test whether A. bahrelghazali could have subsisted on a C4 diet, thus accounting for the d13C composition of its dental tissue. The effects of body mass on the volume of food consumed are taken into account. The outcomes of these simulations indicate that A. bahrelghazali could have subsisted on a diet of predominantly sedges, albeit with limitations. At higher energy requirements, i.e., above 3.5 times the BMR, it would be difficult for a medium-sized primate to obtain sufficient energy from a sedge-based diet. This is apparently due to constraints on foraging/ feeding time, not because of the nutritional value of sedges per se. These results are discussed against the backdrop of A. bahrelghazali biogeography, palaeoenvironment, and phylogeny. The combined evidence makes it plausible to suggest that Northern Chad may have been a refugium for migrating mammals, including hominins, and throws new light on the deep history of A. bahrelghazali.
    Journal of Human Evolution 10/2015; 87. DOI:10.1016/j.jhevol.2015.06.009 · 3.73 Impact Factor
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    • "Please cite this article in press as: Thompson, J.C., et al., Taphonomy of fossils from the hominin-bearing deposits at Dikika, Ethiopia, Journal of Human Evolution (2015), DRP area have been presented elsewhere (Alemseged et al., 2005; Wynn et al., 2006; McPherron et al., 2010). Specimens collected using Protocols 1 and 2 were scrutinized to provide a general overview of surface modifications across the DRP area. "
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    ABSTRACT: Two fossil specimens from the DIK-55 locality in the Hadar Formation at Dikika, Ethiopia, are contemporaneous with the earliest documented stone tools, and they collectively bear twelve marks interpreted to be characteristic of stone tool butchery damage. An alternative interpretation of the marks has been that they were caused by trampling animals and do not provide evidence of stone tool use or large ungulate exploitation by Australopithecus-grade hominins. Thus, resolving which agents created marks on fossils in deposits from Dikika is an essential step in understanding the ecological and taphonomic contexts of the hominin-bearing deposits in this region and establishing their relevance for investigations of the earliest stone tool use. This paper presents results of microscopic scrutiny of all non-hominin fossils collected from the Hadar Formation at Dikika, including additional fossils from DIK-55, and describes in detail seven assemblages from sieved surface sediment samples. The study is the first taphonomic description of Pliocene fossil assemblages from open-air deposits in Africa that were collected without using only methods that emphasize the selective retention of taxonomically-informative specimens. The sieved assemblages show distinctive differences in faunal representation and taphonomic modifications that suggest they sample a range of depositional environments in the Pliocene Hadar Lake Basin, and have implications for how landscape-based taphonomy can be used to infer past microhabitats. The surface modification data show that no marks on any other fossils resemble in size or shape those on the two specimens from DIK-55 that were interpreted to bear stone tool inflicted damage. A large sample of marks from the sieved collections has characteristics that match modern trampling damage, but these marks are significantly smaller than those on the DIK-55 specimens and have different suites of characteristics. Most are not visible without magnification. The data show that the DIK-55 marks are outliers amongst bone surface damage in the Dikika area, and that trampling is not the most parsimonious interpretation of their origin. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Journal of Human Evolution 08/2015; DOI:10.1016/j.jhevol.2015.06.013 · 3.73 Impact Factor
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    • "), respectively, of the Hadar Formation (Alemseged et al., 2005, 2006). The Dikika fauna indicates that the paleohabitat was a mesic deltaic habitat with a higher proportion of grassland than at the contemporaneous site of Hadar. "
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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; 101. DOI:10.1016/j.jafrearsci.2014.09.019 · 1.40 Impact Factor
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