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      A morphometric analysis of hominin teeth attributed to Australopithecus, Paranthropus and Homo

      research-article
      South African Journal of Science
      Academy of Science of South Africa
      Plio-Pleistocene, molar variability, taxonomy, log se m, analogue species

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          Abstract

          Teeth are the most common element in the fossil record and play a critical role in taxonomic assessments. Variability in extant hominoid species is commonly used as a basis to gauge expected ranges of variability in fossil hominin species. In this study, variability in lower first molars is visualised in morphospace for four extant hominoid species and seven fossil hominin species. A size-versus-shape-based principle component analysis plot was used to recognise spatial patterns applicable to sexual dimorphism in extant species for comparison with fossil hominin species. In three African great ape species, variability occurs predominantly according to size (rather than shape), with the gorilla sample further separating into a male and a female group according to size. A different pattern is apparent for the modern human sample, in which shape variability is more evident. There is overlap between male and female modern humans and some evidence of grouping by linguistic/tribal populations. When fossil hominin species are analysed using equivalent axes of variance, the specimens group around species holotypes in quite similar patterns to those of the extant African great apes, but six individual fossil molars fall well outside of polygons circumscribing holotype clusters; at least three of these specimens are of interest for discussion in the context of sexual dimorphism, species variability and current species classifications. An implication of this study is that, especially in the case of modern humans, great caution needs to be exercised in using extant species as analogues for assessing variability considered to be a result of sexual dimorphism in fossil hominin species.

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          Jaw movement and tooth use in recent and fossil primates.

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            Sexual dimorphism in Australopithecus afarensis was similar to that of modern humans.

            The substantial fossil record for Australopithecus afarensis includes both an adult partial skeleton [Afar Locality (A.L.) 288-1, "Lucy"] and a large simultaneous death assemblage (A.L. 333). Here we optimize data derived from both to more accurately estimate skeletal size dimorphism. Postcranial ratios derived from A.L. 288-1 enable a significant increase in sample size compared with previous studies. Extensive simulations using modern humans, chimpanzees, and gorillas confirm that this technique is accurate and that skeletal size dimorphism in A. afarensis was most similar to that of contemporary Homo sapiens. These data eliminate some apparent discrepancies between the canine and skeletal size dimorphism in hominoids, imply that the species was not characterized by substantial sexual bimaturation, and greatly increase the probability that the reproductive strategy of A. afarensis was principally monogamy.
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              Re-appraisal of the stratigraphy and determination of new U-Pb dates for the Sterkfontein hominin site, South Africa.

              Sterkfontein Caves is the single richest early hominin site in the world with deposits yielding one or more species of Australopithecus and possible early Homo, as well as an extensive faunal collection. The inability to date the southern African cave sites accurately or precisely has hindered attempts to integrate the hominin fossil evidence into pan-African scenarios about human evolutionary history, and especially hominin biogeography. We have used U-Pb and U-Th techniques to date sheets of calcium carbonate flowstone inter-bedded between the fossiliferous sediments. For the first time, absolute age ranges can be assigned to the fossil-bearing deposits: Member 2 is between 2.8 +/- 0.28 and 2.6 +/- 0.30 Ma and Member 4 between 2.65 +/- 0.30 and 2.01 +/- 0.05 Ma. The age of 2.01 +/- 0.05 Ma for the top of Member 4 constrains the last appearance of Australopithecus africanus to 2 Ma. In the Silberberg Grotto we have reproduced the U-Pb age of approximately 2.2 Ma of for the flowstones associated with StW573. We believe that these deposits, including the fossil and the flowstones, accumulated rapidly around 2.2 Ma. The stratigraphy of the site is complex as sediments are exposed both in the underground chambers and at surface. We present a new interpretation of the stratigraphy based on surface mapping, boreholes logs and U-Pb ages. Every effort was made to retain the Member system, however, only Members 2 and 4 are recognized in the boreholes. We propose that the deposits formally known as Member 3 are in fact the distal equivalents of Member 4. The sediments of Members 2 and 4 consisted of cone-like deposits and probably never filled up the cave. The U-Th ages show that there are substantial deposits younger than 400 ka in the underground cave, underlying the older deposits, highlighting again that these cave fills are not simple layer-cakes.
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                Author and article information

                Contributors
                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
                December 2016
                : 112
                : 11-12
                : 1-15
                Affiliations
                [01] Johannesburg orgnameUniversity of the Witwatersrand orgdiv1School of Geosciences orgdiv2Evolutionary Studies Institute South Africa
                Article
                S0038-23532016000600021
                10.17159/sajs.2017/20160136
                7b4fc139-4883-41e4-9c62-462ad172a02a

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

                History
                : 09 May 2016
                : 06 September 2016
                : 19 August 2016
                Page count
                Figures: 0, Tables: 0, Equations: 0, References: 79, Pages: 15
                Product

                SciELO South Africa


                Plio-Pleistocene,molar variability,taxonomy,log se m,analogue species

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