Early Hominids Had a Taste for Grass

The nearly 2-million-year-old Paranthropus boisei was the cow of the hominid family. Unlike other human cousins, the species was a fan of dining on grasses. But it turns out it wasn’t the only, or even the first, hominid grazer. Australopithecus bahrelghazali was munching on grasses and sedges at least 1.5 million years before the origin of P. boisei, a new study in the Proceedings of the National Academy of Sciences suggests. The findings may mean early hominids were capable of consuming a wide variety of foods and colonizing new environments.

But before we discuss how scientists figured out A. bahrelghazali‘s diet, and why that matters, we need to address a far more pressing question: Who the heck was A. bahrelghazali?

In 1993, researchers in Chad unearthed a 3.5-million-year-old hominid lower jaw fragment and a few attached teeth. Based on the fossils’ age, many paleoanthropologists think the bones belonged to Australopithecus afarensis. But the specimen was found more than 1,500 miles farther west than any other A. afarensis bones, and subtle differences in the size and shape of the fossils led the discoverers to conclude they had found a new species. They named it A. bahrelghazali after the Bahr el Ghazal valley in Chad where the bones were recovered. Since then, researchers haven’t found any other A. bahrelghazali fossils and its species’ status remains controversial.

With just a jaw and teeth, there’s not too much scientists can say about what A. bahrelghazali looked like or how it lived its life. But, fortunately, diet is something that can be gleamed from these fossils. Analyzing the teeth’s chemistry is one way to assess what the species ate. This is possible because the carbon found in plants comes in two versions, or isotopes, called C3 and C4. Trees and other forest plants are rich in C3; grasses, sedges and other grassland plants have an abundance of C4. When an animal eats these plants—or eats other animals that eat these plants—the different carbon isotopes get incorporated into the individual’s teeth, serving as a record of what it once ate. Previous work on P. boisei has shown that C4 plants made up as much as 77 percent of that hominid’s diet.

In the new study, Julia Lee-Thorp of Oxford University and colleagues come to a similar conclusion for A. bahrelghazali, that the species mainly ate C4 plants, probably grasses and sedges. And like modern baboons that live on savannas, the hominid probably ate different parts of these plants, including underground tubers and bulbs. This diet is not surprising given the type of habitat A. bahrelghazali lived in. Based on the other types of animals found near the hominid, the researchers say A. bahrelghazali made its home in an open grassland, with few trees, near a lake. So forest foods weren’t really a dining option.

The results mean that by 3.5 million years ago hominids were probably already “broad generalists” capable of eating a variety of foods depending on what was locally available, the researchers say. (The younger Australopithecus sediba,which lived roughly 2 million years ago, demonstrates some of the stranger foods that hominids could eat: The South African species liked to eat wood—a dietary preference not seen in any other hominid.) Being a food generalist may have allowed A. bahrelghazali to explore new environments and leave behind the forests that earlier hominids, such as Ardipithecus ramidus, and their ancestors resided in.

Erin Wayman | | READ MORE

Erin Wayman is a science and human evolution blogger for Hominid Hunting. She has M.As in biological anthropology and science writing.