IT WAS the first fussy eater. Most ancient hominins ate a broad diet, but one species specialised on sedges, which might have led to its downfall.
鈥�Australopithecus bahrelghazali is probably the most enigmatic of all the australopiths,鈥� says at the University of Oxford. Its ancestors strayed from East Africa鈥檚 Rift Valley 鈥� the stronghold of ape-like hominins 鈥� and headed west around 4 million years ago when the region was . By 3.6 million years ago, A. bahrelghazali reached what is now Chad 鈥� settling a few thousand kilometres further west than any other australopith yet found.
鈥淭hese ape-like hominins got stuck exploring Africa鈥檚 wild west as the climate changed鈥�
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Macho鈥檚 work suggests that on the journey west (see diagram), the hominin adapted in a bizarre way. We know from isotope analysis that A. bahrelghazali ate a diet rich in so-called C4 plants. Grasses and tubers are common plants of this type, but Macho says the hominin鈥檚 flat molars with thin enamel couldn鈥檛 have processed such tough and abrasive foods. Instead, it must have fed on softer C4 plants, like sedges. But no primate today specialises in eating this kind of vegetation, which is fibrous and takes a long time to process. 鈥淐ould a large-brained hominin be sustained by these foods?鈥� asks Macho.
Macho鈥檚 analysis of baboons, which eat sedges as a part of a broader diet, suggests the answer is yes 鈥� but only just. A. bahrelghazali would have got enough energy to maintain its basic metabolic rate, but probably struggled to build up the energy reserves needed for avoiding predators (Journal of Human Evolution, ).
Unlike East Africa, though, its new home was rich in sedges and largely predator-free, says Macho, allowing for a quiet life and a lot of time for eating. Yet such a restricted diet would have left it more vulnerable to extinction if the habitat changed. As the climate dried out, A. bahrelghazali would have become isolated from its eastern australopith cousins and it eventually went extinct. 鈥淭he idea that A. bahrelghazali was a lost branch of hominin that migrated west and then got stuck is a very sensible one,鈥� says at University College London.
This article appeared in print under the headline 鈥淔ussy eating may have doomed ape-like humans鈥�
