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Limb-size proportions in Australopithecus afarensis and Australopithecus africanus
David J Green1, Adam D Gordon, Brian G Richmond
1Center for the Advanced Study of Hominid Paleobiology, Department of Anthropology, The George Washington University, 2110 G St. NW, Washington, DC 20052, USA. djgreen@gwu.edu
Journal of Human Evolution
|October 20, 2006
Summary
Australopithecus africanus had more apelike limb proportions than Australopithecus afarensis, suggesting different evolutionary paths. This study used a new Monte Carlo method to analyze fossil limb proportions, confirming significant differences between these hominin species.
Area of Science:
- Paleoanthropology
- Primate Anatomy
- Evolutionary Biology
Background:
- Previous studies suggested Australopithecus africanus had more apelike limb proportions than Australopithecus afarensis.
- Limited support existed due to errors in estimating limb length and body size.
Purpose of the Study:
- To test the hypothesis that A. africanus had greater upper:lower limb-size proportions than A. afarensis.
- To statistically assess interspecific differences among A. africanus, A. afarensis, extant apes, and humans.
Main Methods:
- Developed a novel Monte Carlo method to constrain sampling of extant ape and human measurements.
- Reduced comparative postcranial measurements to sizes comparable to fossil samples.
- Calculated composite limb-size ratios for fossils and comparative taxa.
Main Results:
- A. afarensis limb proportions were similar to humans and significantly different from great apes.
- A. africanus limb proportions were similar to great apes and significantly different from humans and A. afarensis.
- Limb-size proportions in extant taxa correlated with positional behaviors.
Conclusions:
- Results strongly support A. africanus having more apelike limb proportions than A. afarensis.
- Suggests A. africanus evolved from a more primitive ancestor or had secondarily derived apelike proportions.
- Arboreal posture and locomotion may have been more significant for A. africanus than A. afarensis.
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