|Title||Was Australopithecus anamensis ancestral to A. afarensis? A case of anagenesis in the hominin fossil record|
|Publication Type||Journal Article|
|Year of Publication||2006|
|Authors||Kimbel, W, Lockwood, C, Ward, C, Leakey, M, Rak, Y, Johanson, D|
|Journal||Journal of Human Evolution|
|Pagination||134 - 152|
|Keywords||A. afarensis, A. anamensis, australopithecines, ethiopia, kenya, phylogeny, tanzania|
We tested the hypothesis that early Pliocene Australopithecus anamensis was ancestral to A. afarensis by conducting a phylogenetic analysis of four temporally successive fossil samples assigned to these species (from earliest to latest: Kanapoi, Allia Bay, Laetoli, Hadar) using polarized character-state data from 20 morphological characters of the dentition and jaws. If the hypothesis that A. anamensis is ancestral to A. afarensis is true, then character-state changes between the temporally ordered site-samples should be congruent with hypothesized polarity transformations based on outgroup (African great ape) conditions. The most parsimonious reconstruction of character-state evolution suggests that each of the hominin OTUs shares apomorphies only with geologically younger OTUs, as predicted by the hypothesis of ancestry (tree length = 31; Consistency Index = 0.903). This concordance of stratigraphic and character-state data supports the idea that the A. anamensis and A. afarensis samples represent parts of an anagenetically evolving lineage, or evolutionary species. Each site-sample appears to capture a different point along this evolutionary trajectory. We discuss the implications of this conclusion for the taxonomy and adaptive evolution of these early-middle Pliocene hominins.
|Short Title||Journal of Human Evolution|
Was Australopithecus anamensis ancestral to A. afarensis? A case of anagenesis in the hominin fossil record
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