Was Australopithecus anamensis ancestral to A. afarensis? A case of anagenesis in the hominin fossil record

William Kimbel, Charles A. Lockwood, Carol V. Ward, Meave G. Leakey, Yoel Rak, Donald Johanson

Research output: Contribution to journalArticle

115 Scopus citations

Abstract

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.

Original languageEnglish (US)
Pages (from-to)134-152
Number of pages19
JournalJournal of human evolution
Volume51
Issue number2
DOIs
StatePublished - Aug 2006

Keywords

  • Anagenesis
  • Australopithecus afarensis
  • Australopithecus anamensis
  • Hominin

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Anthropology

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