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      Temporal ranges and ancestry in the hominin fossil record: The case of Australopithecus sediba

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          Abstract

          In attempting to resolve the phylogenetic relationships of fossil taxa, researchers can use evidence from two sources - morphology and known temporal ranges. For most taxa, the available evidence is stronger for one of these data sources. We examined the limitations of temporal data for reconstructing hominin evolutionary relationships, specifically focusing on the hypothesised ancestor-descendant relationship between Australopithecus sediba and the genus Homo. Some have implied that because the only known specimens of A. sediba are dated to later than the earliest fossils attributed to Homo, the former species is precluded from being ancestral to the latter. However, A. sediba is currently known from one site dated to 1.98 Ma and, thus, its actual temporal range is unknown. Using data from the currently known temporal ranges of fossil hominin species, and incorporating dating error in the analysis, we estimate that the average hominin species' temporal range is ~0.97 Myr, which is lower than most figures suggested for mammalian species generally. Using this conservative figure in a thought experiment in which the Malapa specimens are hypothesised to represent the last appearance date, the middle of the temporal range, and first appearance date for the species, the first appearance date of A. sediba would be 2.95, 2.47 and 1.98 Ma, respectively. As these scenarios are all equally plausible, and 2.95 Ma predates the earliest specimens that some have attributed to Homo, we cannot refute the hypothesis that the species A. sediba is ancestral to our genus based solely on currently available temporal data. SIGNIFICANCE: • We correct a common misconception in palaeoanthropology that a species currently known only from later in time than another species cannot be ancestral to it. • On temporal grounds alone one cannot dismiss the possibility that A. sediba could be ancestral to the genus Homo.

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          A new evolutionary law

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            Australopithecus sediba: a new species of Homo-like australopith from South Africa.

            Despite a rich African Plio-Pleistocene hominin fossil record, the ancestry of Homo and its relation to earlier australopithecines remain unresolved. Here we report on two partial skeletons with an age of 1.95 to 1.78 million years. The fossils were encased in cave deposits at the Malapa site in South Africa. The skeletons were found close together and are directly associated with craniodental remains. Together they represent a new species of Australopithecus that is probably descended from Australopithecus africanus. Combined craniodental and postcranial evidence demonstrates that this new species shares more derived features with early Homo than any other australopith species and thus might help reveal the ancestor of that genus.
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              Origin and Evolution of the Elephantidae

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                Author and article information

                Contributors
                Role: ND
                Role: ND
                Role: ND
                Role: ND
                Journal
                sajs
                South African Journal of Science
                S. Afr. j. sci.
                Academy of Science of South Africa (Pretoria, Gauteng, South Africa )
                0038-2353
                1996-7489
                April 2018
                : 114
                : 3-4
                : 1-7
                Affiliations
                Bronx New York orgnameBronx Community College (CUNY) orgdiv1Department of Biological Sciences USA
                Texas orgnameTexas A & M University orgdiv1Department of Anthropology USA
                Calgary orgnameUniversity of Calgary orgdiv1Department of Anthropology and Archaeology Canada
                Article
                S0038-23532018000200020
                10.17159/sajs.2018/20170327

                This work is licensed under a Creative Commons Attribution 4.0 International License.

                Page count
                Figures: 0, Tables: 0, Equations: 0, References: 67, Pages: 7
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