New australopithecine described

April 8, 2010 • 11:26 am

by Greg Mayer

Lee Berger of the University of the Witwatersrand and several colleagues will be describing a new species of Australopithecus, A. sediba, from 1.78 to 1.95 million-year-old deposits in South Africa, in tomorrow’s issue of Science. The issue will also have a geological article on the find by Paul H.G.M. Dirks of James Cook University, Queensland, and colleagues, and a news item, all available now at Science‘s website (plus a podcast and video). The description is based on two partial skeletons, including a well preserved juvenile skull, most of the right arm and shoulder girdle, parts of the hip and leg, and various other bits.

Skull of juvenile Australopithecus sediba. Image from University of the Witwatersrand.

The new species has a long arm, but the pelvis and leg indicate that it was bipedal (i.e. it could both climb and walk upright). The general evolutionary conclusion the authors draw is the mosaic nature of the origin of Homo features: some Homo-like characters evolved before others, e.g. bipedality preceding cranial enlargement. They find specific features linking the new species to Homo, and posit it to be intermediate between earlier australopithecines and Homo:

The age and overall morphology of Au. sediba imply that it is most likely descended from Au. africanus, and appears more derived toward Homo than do Au. afarensis, Au. garhi, and Au. africanus.

Something I rather liked about the paper is that it is quite data rich, having tables of comparison of traits and measurements of the new find and several other fossil hominids. Such data-richness is unusual for papers in Science, which prefers short papers, with data often being relegated to electronic appendices or other papers; the Berger et al. paper is an unusual ten pages long.

The news has already reached media websites (e.g. the New York Times, the BBC and the Telegraph). Unlike the case of Darwinius masillae, however, in which premature press coverage, which included the name and its diagnostic characters, and web posting of the description, led to questions about the proper authorship and publication of the name, the authors and journalists in this case have done everything right. The news accounts are appearing coincident with the name being published (i.e. printed on paper), not prior to its publication. (The newspaper pieces linked to above are online now, but they won’t be published in the sense of the International Code of Zoological Nomenclature until tomorrow, when the scientific paper itself will be published.) There will thus be no questions about the publication of the name; the authors have made sure that, as the ICZN recommends, Australopithecus sediba is “self-evidently published within the meaning of the Code” (ICZN, Rec. 8B)