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Nutcracker Man had a taste for grass

U. COLORADO (US) — An ancient, bipedal hominid sporting huge molars preferred to slurp up vast quantities of grass, instead of crunching on the food that earned it the nickname Nutcracker Man.

Nutcracker Man (Paranthropus boisei) ranged across the African landscape more than 1 million years ago and lived side-by-side with direct ancestors of humans. It had long been assumed the hominid favored nuts, seeds, and hard fruit because of its huge jaws, powerful jaw muscles, and the biggest and flattest molars of any known hominid in the anthropological record.

But teeth wear marks indicated soft fruit and grasses were more likely the food of choice.  That evidence, combined with new research measuring the carbon isotopes embedded in fossil teeth to infer diet, indicates the rugged jaw and large, flat tooth structure may have been just the ticket for Paranthropus boisei to mow down and swallow huge amounts of grasses or sedges at a single sitting.

“Frankly, we didn’t expect to find the primate equivalent of a cow dangling from a remote twig of our family tree,” says Matt Sponheimer, professor of anthropology at the University of Colorado.

The new research is reported in the journal of the Proceedings of the National Academy of Sciences.

“Fortunately for us, the work of several research groups over the last several years has begun to soften prevailing notions of early hominid diets,” Sponheimer says.”³If we had presented our new results at a scientific meeting 20 years ago, we would have been laughed out of the room.”

For the new study, researchers led by Thure Cerling, professor at the University of Utah, removed tiny amounts of enamel from 22 Paranthropus boisei teeth collected in central and northern Kenya, each of which contained carbon isotopes absorbed from the types of food eaten during the lifetime of each individual.

In tropical environments, virtually all trees and bushes—including fruits and leaves—use the so-called C3 photosynthetic pathway to convert sunlight into energy, while savannah grasses and some sedges use the C4 photosynthetic pathway.

The isotope analysis indicated Paranthropus boisei individuals were much bigger fans of C4 grasses and sedges than C3 trees, shrubs, and bushes. The results indicated the collective diet of the 22 individuals averaged about 77 percent grasses and sedges for a period lasting at least 500,000 years.

The carbon isotope ratios of Paranthropus teeth were also compared with the teeth of other grazing mammals living at the same time and in the same area, including ancestral zebras, hippos, warthogs, and pigs. Those mammals were eating primarily C4 grasses, virtually identical to Paranthropus boisei. “They were eating at the same table,” says  Cerling.

The Nutcracker Man was part of a line of close human relatives known as australopithecines that includes the famous 3-million-year-old Ethiopian fossil Lucy, seen by some as the matriarch of modern humans.

Roughly 2.5 million years ago, the australopithecines are thought to have split into the genus Homo—which produced modern Homo sapiens—and the genus Paranthropus, that reached a dead-end.

“One key result is that this hominid had a diet fundamentally different from that of all living apes, and, by extension, favored very different environments,” Sponheimer says.

“And having a good idea of where these ancient creatures lived and what they ate helps us understand why some early hominids left descendants and others did not.”

The first skull of a Paranthropus boisei individual was discovered by co-author Meave Leakey¹s in-laws, Mary and Louis Leaky, in 1959 in Tanzania.

In 2006, a team led by Sponheimer found that a cousin of Paranthropus boisei known as Paranthropus robustus had a far more diverse diet, consisting of fruits, nuts, grasses, and perhaps even animals, clouding the notion that it was driven to extinction by its picky eating habits.

So what led to the end of the line for Paranthropus?  It could well have been direct competition with Homo—which was becoming skilled in extensive bone and stone technology—or it could have been a variety of other issues, including a slower reproductive rate for Paranthropus than for Homo, Sponheimer says.

Researchers from Stony Brook University and the University of Utah contributed to the study, that was funded in part by the National Science Foundation.

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