The diet of Australopithecus sediba

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July 01, 2012

This is the title of a paper appearing last week in the journal Nature.  A careful examination of fossilized tooth enamel and a plaque from this intriguing (and controversial) taxon discovered at a site called Malapa in South Africa in 2008, provides a detailed insight to the diet of one species of hominin at a particular place and time.

The excavations at Malapa have yielded two remarkably complete skeletons, one that of an adult female and the other a juvenile male.  Amanda Henry and her Max Planck Institute team of researchers have determined these two individuals living in a predominantly savanna like habitat, found a variety of food resources in woodland environments, at least at the very end of their lives. (Fossilized tooth enamel and plaque contain the chemical signatures of foods consumed only in the last days of the organisms’ existence, not a lifelong record.)

The abstract of this paper reads as follows:
“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.”

Dr. William H Kimbel is Director of the Institute of Human Origins at Arizona State University and in an interview with MS-NBC stated "...[the findings are consistent with the view] early hominins were quite flexible with respect to diet, with different populations preferring different parts of the available plant resource base, depending on when they lived, and where...The plant phytoliths are a nice addition to the repertoire of perspectives on the issue."

The MS NBC interviewer pressed Kimbel on the extent to which the diet of Au. sediba compared with the diet of modern Chimpanzees. Kimbel replied, "I don't think sediba should be seen as 'remarkable' in this context... "And sediba no more belongs in the 'chimp camp' than it does in the 'giraffe camp' (with which it also shares dominant C3 values).This is not a useful analogy."

In response to a question from BecomingHuman as to how plaque, the material that cakes on our teeth and one of the reasons we have dental hygenists clean our teeth, can fossilize and even after millions of years tell us what our ancestors ate, Dr Gary Schwartz of the Institute of Human Origins said in  an email:

"Yes, you can get fossilized plaque, or tartar, or calculus (tartar and calculus are the same thing: hardened plaque).  It is a buildup of bacteria, minerals, etc., that precipitate out from saliva and adhere to dental surfaces.  As such, they can accumulate bits of food, and a variety of any other particle that finds its way into an organism's mouth. Any organic matrix, like bone or plaque/calculus can become fossilized, as fossilization is simply just the replacement over time of organic material with inorganic material. So, in that sense, this is a really exciting and interesting study in focusing on an underused feature of the dentition: fossil plaque.  How it survives is the same manner in which how any organic material (bone) survives: luck!"

These Malapa fossils are intriguing because while their postcrania are definitely australopithecine there are aspects of the cranial anatomy more like those of Homo.  Adding controversy to this mix ofanatomival features, Lee Berger, who discovered these remains, and attributed them to Australopithecus, claims this newly named taxon, dated to 1.9 7 million years ago, is ancestral to Homo.  This claim has been met with skepticism from other scientists, who point out a maxilla (upper jaw) found at Hadar, Ethiopia by Dr. Kimbel predates these Au. sediba specimens by at least 300,000 years.  Thus, Au. sediba cannot be said to be ancestral to the genus Homo, the earliest example of which was found in remote northern Africa and determined to be considerably older.

Read the Nature article.

A brief MS-NBC video shows Dr Passey, one of the team members, explaining their methodology and conclusion.  Find the video here.