The authors of a new research paper introduce their findings with the statement: "Early hominin diet is central to the study of human origins". Analysis of carbon isotopes is revealing for the kind of plant material consumed. Two important fingerprints are identifiable: from C3 resources and from C4 resources. In the C3 category are the leaves and fruits of trees, shrubs, plus some herbs, and animals eating these plants. The C4 category signifies (most) tropical grasses, sedges, and animals eating these plants. Modern chimpanzees consume C3 foods, even when grasses are plentiful. The fossil hominids are associated with savannah environments and C4 foods were dominant in their diet. The new work concerns two specimens of Australopithecus sediba from the site of Malapa, South Africa. For a previous blog on this species, go here.
"The A. sediba diet was analyzed using a technique that involved zapping fossilized teeth with a laser, said [co-author] Sandberg. The laser frees telltale carbon from the enamel of teeth, allowing scientists to pinpoint the types of plants that were consumed and the environments in which the hominids lived. The carbon signals from the teeth are split into two groups: C3 plants like trees, shrubs and bushes preferred by A. sediba, and C4 plants like grasses and sedges consumed by many other early hominids." (Source here)
A high-tech dental analysis of a 2-million-year-old hominid from South Africa indicates it had a unique diet that included trees, bushes and fruits. (Credit: Photo courtesy Paul Sandberg, University of Colorado, source here)
The findings were unexpected. We should remember that numerous papers have been published on the available fossil material for Australopithecus sediba that have made a case for considering this species a key transitional form. Those anthropologists advancing this view expected to find a diet dominated by C4 food resources.
"What fascinates me is that these individuals are oddballs," said [co-author] Sponheimer. "I had pretty much convinced myself that after four million years ago most of our hominid kin had diets that were different from living apes, but now I am not so sure." (source here)
and ""It seems like a hallmark of human evolution to be able to use savanna resources," [co-author] Passey told me. "Today, most of our energy comes from grass in one way or another, either from grain or from animals that eat grain and grass." (source here)
The authors and others favouring Australopithecus sediba as a human ancestor have not changed their views on this particular matter. They write: "Previous analyses have shown that Au. sediba has an unusual suite of morphological features, and our results present new oddities and questions." However, those of us who were not persuaded by the original research analyses, and who consider the australopithecines are an extinct family of apes (for the reasons, go here), draw a different conclusion from the data. Their diet reveals that they did not feed in savannah environments and that they were at home in trees where they could eat leaves and fruit. We should bear in mind that convergence is pervasive in the record of life and that "shared skeletal morphology does not always mean shared recent evolutionary history". Consequently, the evidence from diet gives strong reinforcement to the previous conclusion that Australopithecus sediba is an extinct ape, and we have no reason to consider them (in the words of Science Daily) "ancient human ancestors".
The diet of Australopithecus sediba
Amanda G. Henry, Peter S. Ungar, Benjamin H. Passey, Matt Sponheimer, Lloyd Rossouw, Marion Bamford, Paul Sandberg, Darryl J. de Ruiter & Lee Berger
Nature, Published online 27 June 2012 | doi:10.1038/nature11185
Specimens of Australopithecus sediba from the site of Malapa, South Africa (dating from approximately 2 million years (Myr) ago) present a mix of primitive and derived traits that align the taxon with other Australopithecus species and with early Homo. Although much of the available cranial and postcranial material of Au. sediba has been described, its feeding ecology has not been investigated. Here we present results from the first extraction of plant phytoliths from dental calculus of an early hominin. We also consider stable carbon isotope and dental microwear texture data for Au. sediba in light of new palaeoenvironmental evidence. The two individuals examined consumed an almost exclusive C3 diet that probably included harder foods, and both dicotyledons (for example, tree leaves, fruits, wood and bark) and monocotyledons (for example, grasses and sedges). Like Ardipithecus ramidus (approximately 4.4 Myr ago) and modern savanna chimpanzees, Au. sediba consumed C3 foods in preference to widely available C4 resources. The inferred consumption of C3 monocotyledons, and wood or bark, increases the known variety of early hominin foods. The overall dietary pattern of these two individuals contrasts with available data for other hominins in the region and elsewhere.
Ancient Human Ancestors Had Unique Diet, ScienceDaily (June 27, 2012)
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