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

doi:10.1016/j.jhevol.2006.02.003

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 journal › Article › peer-review

142 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 language	English (US)
Pages (from-to)	134-152
Number of pages	19
Journal	Journal of human evolution
Volume	51
Issue number	2
DOIs	https://doi.org/10.1016/j.jhevol.2006.02.003
State	Published - Aug 2006

Keywords

Anagenesis
Australopithecus afarensis
Australopithecus anamensis
Hominin

ASJC Scopus subject areas

Ecology, Evolution, Behavior and Systematics
Anthropology

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10.1016/j.jhevol.2006.02.003

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@article{fa963757bbed4f1fb9808388c3914935,

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

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.",

keywords = "Anagenesis, Australopithecus afarensis, Australopithecus anamensis, Hominin",

author = "William Kimbel and Lockwood, {Charles A.} and Ward, {Carol V.} and Leakey, {Meave G.} and Yoel Rak and Donald Johanson",

note = "Funding Information: We thank Zeresenay Alemseged, Mark Maslin, Peter Ungar, Kaye Reed, Chris Campisano, Lucas Delezene, and Laura Stroik for helpful discussion and/or comments on the manuscript. Thoughtful reviews by anonymous referees and an Associate Editor of JHE were helpful in bringing the ms. to final form. Lucas Delezene and Matthew Tocheri were of invaluable assistance with the scanning facilities in the PRISM visualization lab at ASU. We are grateful to Denise To for the artwork in Figure 4 . Final preparation of this paper was conducted while WHK was on sabbatical at University College London, facilitated by a Leverhulme Trust Visiting Professorship. Fieldwork leading to the discovery of the Hadar and Kanapoi fossils, which stimulated this collaborative research, was funded by the National Science Foundation (Hadar, Kanapoi), the National Geographic Society (Hadar, Kanapoi), and the Institute of Human Origins (Hadar). We thank the governments of Ethiopia and Kenya for permission to carry out the field work at Hadar and Kanapoi, respectively, and the National Museums of Ethiopia and Kenya for logistical support during all phases of the research. ",

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doi = "10.1016/j.jhevol.2006.02.003",

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AU - Leakey, Meave G.

AU - Rak, Yoel

AU - Johanson, Donald

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

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Keywords

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