Laser dentistry has helped researchers discover more about the diets of our early human relatives. University of Utah scientists improved a method of testing fossil teeth, and showed that early human relatives varied their diets with the seasons 1.8 million years ago, eating leaves and fruit when available in addition to seeds, roots, tubers and perhaps grazing animals.

Early human relatives varied their diets

Study co-author and geochemist Dr Thure Cerling says the study of the now-extinct, ape-like species known as Paranthropus robustus is important because it “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 utilise foods from all over the world.”

The researchers used a laser to remove tiny samples from four 1.8-million-year-old fossilised Paranthropus teeth, and then tested the samples to determine the ratios of two isotopes or forms of carbon.

“By analysing 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, a co-author of the study in journal Science.

Passey used a laser to remove and vaporise tiny samples of enamel, which then were analysed in a mass spectrometer to determine 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 drill bit and basically grind away at the tooth, collect the powder and then analyse that,” Passey said.

In the past decade, researchers have used laser ablation to remove and analyse tooth enamel samples from the large, fossilised teeth of prehistoric horses, rhinos and elephants to determine the animals' diets.

Until now, lasers were too destructive to use on the smaller teeth of human ancestors and their relatives – even those of Paranthropus, known for relatively large teeth and a strong, heavy jaw.

Passey improved the laser technique by fine-tuning the method to handle very small samples like human-sized teeth. He 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 samples at various points along the length of the tooth, which is marked by tiny ridges called perikymata. They run parallel to the tooth's crown and represent tooth growth, similar to tree rings. Perikymata are produced under the gums during the animal's juvenile years, when teeth are growing.

Each laser sampling vaporised enamel that formed during several months and thus represented what Paranthropus ate during that period. By taking several samples off the length of each tooth, the researchers reconstructed a few years of each creature's diet.

The research found that plants fall into two broad classes depending on the way in which they use photosynthesis to convert sunlight, water and carbon dioxide into plant matter and oxygen. Carbon isotope ratios revealed the extent to which the relatives of early humans ate so-called C3 plants, which include fruit and leaves from trees in both the forest and savanna, and C4 plants, which grow mostly on the savanna and include potato-like tubers, grasses, and seeds and roots from grasses. If the early hominids ate meat from grass-grazing animals like antelope, the C4 'signal' also showed up in their teeth.

“Hominids were taking advantage of seasonal differences in food items in a savanna environment,” Dr 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.”

Dr Cerling said 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 who had a more restricted diet.”