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

J Hum Evol. 2006 Aug;51(2):134-52. doi: 10.1016/j.jhevol.2006.02.003. Epub 2006 Mar 6.

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Biological Evolution*
  • Dentition*
  • Fossils*
  • Hominidae / anatomy & histology*
  • Jaw / anatomy & histology*