A new method of analyzing fossil teeth allowed scientists to see that early humans had 1.8 million years ago a more varied diet than previously thought.

"The new study shows that Paranthropus robustus,(image) (who lived side by side with Homo species, direct ancestors of modern humans) once thought to be a "chewing machine" specializing in tough, low-quality vegetation, instead had a diverse diet ranging from fruits and nuts to sedges, grasses, seeds and perhaps even animals", said CU-Boulder anthropology Assistant Professor Matt Sponheimer.

Paranthropus was believed to have vanished when the climate dried because of its strict diet. This species was an australopithecine, an evolutionary line close to human that includes the famous Lucy that lived over 3 million years ago, belonging to Australopithecus afarensis species. "One line of Lucy's children ultimately led to modern humans while the other (Paranthropus) was an evolutionary dead end," he said.

"Since we have now shown Paranthropus was flexible in its eating habits over both short and long intervals, we probably need to look to other biological, cultural or social differences to explain its ultimate fate."

"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," Sponheimer said.

Paranthropus was bipedal, 1.2 m (4 feet) tall and weighed less than 100 pounds (40 kg). Its brain was a little larger than a chimp's, but "Paranthropus was not a mental giant," Sponheimer said. Using laser ablation, the team examined carbon isotopes ratios in the teeth from four individuals from the Swartkrans site in South Africa. "By analyzing tooth enamel, we found that they ate lots of different things, and what they ate changed during the year," says University of Utah geology doctoral student Ben Passey.

"We wanted to know if they had variability in their diets on the time scale of a few months to a few years," he says. "The new method showed that their diets were extremely variable. One possibility is that they were migrating seasonally between more forested habitats to more open, savanna habitats."

Thure Cerling - a professor of geology and biology - says the study of Paranthropus "shows that the variability in human diet has been 'in the family' for a very long time. It is this variability that allows modern humans to utilize foods from all over the world."

Plants are divided in two types, depending on the way they make photosynthesis. Many plants are C3 type, mostly forest and savanna species, while C4 plants are better adapted to dry climate and grow on savanna and arid areas, including potato-like tubers forming plants and grasses. If fossil hominids ate meat from grass eating mammals, like gazelles and antelopes, chemical signs of the C4 were present in their teeth. "Hominids were taking advantage of seasonal differences in food items in a savanna environment," Cerling says.
"We cannot tell if they were carnivores or scavengers, but it is possible their diet included animals. We are picking up that signal."

The new laser technique removes and vaporizes tiny samples of enamel, analyzed later in a mass spectrometer to see the ratio of rare carbon-13 to common carbon-12. "The previous way to sample tooth enamel was to take a dental drill with a diamond-impregnated bit and basically grind away at the tooth, collect the powder and then analyze that," Passey says.

"If you tried the previous method on a human tooth, you would blast a hole clear through the enamel, and museum curators wouldn't like that."

The laser was used to remove layers of annual growth of the teeth, so those tiny samples indicated what ate the animal during several months. Several samples of the length of each tooth reconstructed a few years of each individual's alimentation. A high ratio of carbon-13 to carbon-12 means the diet was based on C4 savanna plants, like grass seeds and roots, tubers and sedges, but could also indicate meat from grazers. A low level of carbon 13 indicates a diet oriented on C3 plants: leaves and fruits of trees and shrubs, as well as forbs (broadleafed herbs).

Analyses revealed that the Paranthropus' diet varied in the C3/C4 ratio proportion, both seasonally and yearly. Yearly variation "might reflect yearly differences in rainfall-related food availability", including the onset of droughts which caused individuals to eat foods not normally preferred. "This is the first study to paint a portrait of an early hominid eating its way across a varied landscape. None of us involved in the study dreamed Paranthropus would have had such a variable diet over thousands of years, much less in just a few months time." Sponheimer said.

Researchers think that Paranthropus individuals were shifting between fruit rich forested areas to open savanna, perhaps along sedge-rich waterways. "We've never before been able to see dietary change within a single individual's lifetime," Sponheimer said.

Cerling says the study "shows that our early human relatives were able to eat a varied diet and therefore were more adaptable in savanna environments than other primates which had a more restricted diet."

Previous studies had supposed that the diets of the human ancestors became more varied about 3 million years ago when Africa's climate started getting drier and more seasonal, shortly before the appearance of stone tools and of Paranthropus and genus Homo (to which modern humans belong).

The old theory of a limited dieted Paranthropus being now rejected, scientists have to find other explanations as to why tool using Homo, with also a highly varied diet, survived and evolved. "While anthropologists are confident that the varied diet of early homo species -- including meats and a wide variety of plant species -- helped to propel the line into a successful run on Earth that continues today, the notion that an overly specialized diet doomed Paranthropus to extinction in a changing environment is now in doubt," said Sponheimer.

"Thus, other biological, social or cultural differences may be needed to explain the different fates of Homo and Paranthropus".

Competition with Homo might have eliminated Paranthropus, because the first possessed an extensive bone and stone technology or maybe he had a higher reproductive rate. "Swartkrans is a renowned early hominid cave site containing remains of both Paranthropus robustus and early members of the genus Homo", said Sponheimer.

Inside the cave were found both bone and stone tools used by early hominids, like bone digging sticks, probably used to get termites or tubers, as well as some of the earliest known fire records with animal burned bones.