No Australopithecus boisei from the Afar

I was reading Scott Simpson and colleagues’ article from March 2014, “The female Homo pelvis from Gona: Response to Ruff (2010)”, in which they go through reasons why the BSN49/P27 fossil pelvis belongs to Homo and not, as Ruff has suggested, some version of Australopithecus or Paranthropus.

I blogged about the anatomy of the Gona pelvis (BSN 49/P27) when it was first published in 2008: “Mrs. Elvis, the Homo erectus pelvis”, and raised all the issues that have since become features of the scientific literature. It is a very interesting problem, because BSN49/P27 is only a pelvis; no other skeletal remains have been found from the same individual. Diagnosing pelvic anatomy as belonging to Homo is an interesting problem right now, because of the lack of evidence about pelvic anatomy in late australopiths such as Australopithecus boisei and the presence of Homo-like features in the pelvis of Australopithecus sediba.

I wanted to flag an interesting observation to which I haven’t given much thought before: Au. boisei has not been found at any of the Afar sites. This comes in Simpson and colleagues’ argument that the Gona pelvis BSN49/P27 must be Homo because only Homo has been found in the area during the same time interval.

Finally, Ruff proposed that the Gona pelvis could possibly have been a representative of a species outside of the genus Homo, such as Au. (P.) boisei. Unfortunately, no fossils were allocated to this species in his analysis. No pelvis of Au. (P.) boisei is known and no Australopithecus have been discovered from the Afar region that are younger than 2.5 Ma. Fossils representing the ‘robust’ group were all from Swartkrans and assignable to Au. (P.) robustus. While assigning the Gona pelvis to Au. (P.) boisei might seem like a possibility, the absence of any known comparative material makes this assignment untestable as it is not based on comparative data.

Later in the paper, they reiterate this point:

Despite significant effort surveying for fossils, no specimens attributable to Au. (P.) boisei are known from the Afar region. The Konso, Ethiopia ( Suwa et al., 1997) specimens are the northernmost representatives currently known. Currently, Au. (P.) boisei is not known from any deposits younger than 1.4 Ma ( Suwa et al., 1997). Thus, the 0.9–1.4 Ma Gona pelvis, if it was assignable to Au. (P.) boisei, would be the unique representative from the Afar region and the last appearance datum for this species.

This is perhaps less surprising than it sounds at first, because there are no other Homo specimens reported from Afar during the time span between the date reported for the A.L. 666-1 specimen (2.33 million years) (Kimbel et al. 1997) and the much later Daka specimens (Asfaw et al. 2002) around a million years old. Based on the stratigraphic information published by Simpson et al. (2008), the Gona pelvis lies either within this gap or at the tail end of it.

Amid such a near-total lack of fossil evidence, I wouldn’t readily dismiss the idea that some late australopith may have been present in the Afar area during the Early Pleistocene.

But what would it mean if Au. boisei and other late australopiths really never lived in the Afar area? An absence from Afar would contrast strongly with the Turkana Basin, where Au. boisei is the most common fossil hominin within the sediments leading up to 1.4 million years ago. The Turkana Basin includes a good fraction of southern Ethiopia, where what may be the earliest occurrence of Au. boisei is in the Shungura Formation. The latest occurrence of Au. boisei is also in southern Ethiopia, near Konso. Some recent species do have biogeographic distributions that suggest a split between northeastern and southern Ethiopia; whether such a split was present or relevant for Au. boisei may be worth investigation.

It is a bit odd that no robust australpiths are yet known from North Africa or West Asia. Theropithecus—the genus including living geladas—existed as far as Morocco and India during the Pleistocene. The usual reconstruction of australopiths would suggest they should have been able to disperse effectively through savanna and along rivers and coastlines. Maybe Au. boisei will yet be found outside of its known Rift Valley range.

References

Asfaw, B., Gilbert, W. H., Beyene, Y., Hart, W. K., Renne, P. R., WoldeGabriel, G., ... & White, T. D. (2002). Remains of Homo erectus from Bouri, Middle Awash, Ethiopia. Nature, 416(6878), 317-320. doi:10.1038/416317a

Kimbel, W. H., Johanson, D. C., & Rak, Y. (1997). Systematic assessment of a maxilla of Homo from Hadar, Ethiopia. American Journal of Physical Anthropology, 103(2), 235-262. doi:10.1002/(SICI)1096-8644(199706)103:2<235::AID-AJPA8>3.0.CO;2-S

Ruff, C. (2010). Body size and body shape in early hominins–implications of the Gona Pelvis. Journal of Human Evolution, 58(2), 166-178. doi:10.1016/j.jhevol.2009.10.003

Simpson, S. W., Quade, J., Levin, N. E., Butler, R., Dupont-Nivet, G., Everett, M., & Semaw, S. (2008). A female Homo erectus pelvis from Gona, Ethiopia. Science, 322(5904), 1089-1092. doi:10.1126/science.1163592

Simpson, S. W., Quade, J., Levin, N. E., & Semaw, S. (2014). The female Homo pelvis from Gona: response to Ruff (2010). Journal of human evolution, 68, 32-35. doi:10.1016/j.jhevol.2013.12.004