Published in The Hindu on June 28, 2012

Two fossil specimens of Australopithecus sediba recovered from Malapa, South Africa, present a completely different picture of the type of diet consumed by the early hominins.

Carbon isotope analysis of plant phytoliths (plant-produced silicabodies) extracted from dental calculus (calcified dental plague) and study of dental microwear texture reveal that A. sediba consumed “an almost exclusive C₃ diet,” according to a paper published today (June 28) in Nature . In effect, the discovery expands the known variety of food consumed by early hominins.

The first author is from the Plant Foods and Hominin Dietary Ecology Research Group, Max Plank Institute of Evolutionary Anthropology, Leipzig, Germany.

Similar to chimpanzees

C₃ diet included tree leaves, fruits, wood and bark (dicotyledons) as well as grass and sledges (monocotyledons). Quite surprisingly, A. sediba appears to have had a preference for C₃ diet in lieu of widely available C4, very similar to the modern day savannah chimpanzees. Chimpanzees are known to consume fruits and leaves (C₃ diet) even when C4 diet is in abundance.

“The overall dietary pattern contrasts with data from other hominins in the region and elsewhere,” they write. Incidentally, though A. sediba fossil samples have been extensively studied, this is the first time the dietary pattern has been investigated.

Carbon isotope analysis was carried out on thirty eight phytoliths recovered from the dental calculus of the two specimens. The carbon isotope values of dental calculus fall well outside the range of 81 previously studied African early hominins. This clearly indicates that the diet was nothing but C₃.

Preference for C₃ diet

“The isotope compositions are unusual for hominins and more typical of giraffes” that consume C₃ diet. There is an indication that the hominins had a preference for C₃ diet as the palaeoenvironment of the region from where A. sediba samples were recovered had both C₃ and C4 plants. For instance, sediment samples showed typical evidences of C4 grasses. Evidence collected from Malapa bovid fossils and rodent samples in the area were also indicative of a C₄ diet.

The region probably had “abundant grass and woody vegetation.” Hence the hominins had a choice and were clearly not restricted to one kind of plant type.

And the choice of food was quite varied — fruit, leaf, and wood or bark. The “diversity in phytolith types suggests a varied diet.”

But this is the first ever time that any hominins’ diet has been found to have included wood tissues and bark. “This has not been documented previously,” they stress.

First time ever

So far phytoliths have never been extracted from dental calculus of hominins. Such samples have been recovered only from modern humans and Neanderthals. Phytoliths, which get trapped in dental calculus, are valuable tools in understanding the kind of diet consumed by the specimens.

Even the dental microwear texture analysis suggests the consumption of hard objects.

Despite the overwhelming evidence from both carbon dating and microwear texture analysis, the authors exercise caution when they stress that just two samples have been studied. According to them, there is a need to study more A. sediba samples from the same region.

More so, as the study throws up some contradictions in terms of the area of home ranges. For, if the hominins had been restricted to just a C₃ diet, then they would have required a very large home range. But the variety of C₃ plant materials recovered indicates that the range need not necessarily be large.