Following on the recent announcement that Paranthropus boisei was eating lots of grass and/or some other kind of C4 resources by the Pleistocene, we now have isotopic evidence that Australopithecus bahrelghazali was eating a diet with a similar isotopic composition by about 3 million years ago in north-central Africa (Chad). Keep in mind that that the Chadian australopith is gracile, similar to A. afarensis, so it lacked the mega-chewing apparatus of P. boisei.
It remains to be seen what kind of C4 resources A. bahrelghazali was eating....it could be grass leaves and stems, or maybe the carbohydrate rich tubers and corms of many sedges. Dental microwear data should help to resolve this.
Any way you slice it, it is clear that early hominin diets were diverse....much more diverse than we have previously appreciated.