Tooth analysis may decipher prehistoric diets.

Tooth analysis may decipher prehistoric diets

Scientists say they have indentified the microscopic "fingerprints" of plant remains on the fossil teeth of Gigantopithecus, a huge Asian ape that lived from 6 million to 300,000 years ago. The evidence suggests that the extinct ape -- which stood an estimated 10 feet tall and weighed more than 1,00 pounds -- ate a varied diet, including both tropical fruits and fibrous grasses. If the dental decoding technique proves accurate, it may one day illuminate the feeding habits of other extint animals, including human ancestors.

For now, analyses of plant residues on fossil teeth remain preliminary, says paleoanthropologist Russell Ciochon of the University of Iowa in Iowa City. Indeed, several paleontologists argue that no solid evidence links the tiny particles studied bu Ciochon's group to the diet of living or extinct animals.

A scanning electron microscope revealed 30 floral fingerprints, known as phytoliths, on two out of four Gigantopithecus teeth under study, Ciochon and his co-workers report in the October PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES (Vol. 87, No. 20). Monosilicic acid travels throughout a plant's vascular system and hardens inside and between the cells to create the phytoliths -- remarkably durable silica impressions of the plant cells. Many plants and all grasses absorb the monosilicic acid as their roots take up groundwater.

"Phytliths are widespread throughout the plant kingdom," says archaeologist and study participant Dolores R. Piperno of the Smithsonian Tropical Research Institute in Balboa, Panama.

Scientists first identified phytoliths nearly 150 years ago in Germany, and studies of phytoliths found in soil began in the 1950s. Since then, the hardy silica bits have turned up on stone tools un-earthed at several archaeological sites. Piperno has identified phytoliths from more than 1,300 species of tropical plants, mainly in South America, as well as 19 plant species from three families native to a region of China where Gigantopithecus teeth and jaws have been found.

With Piperno's data in hand, the researchers identified silica bits on the Gigatopithecus teeth as belonging to a family of fibrous grasses that includes bamboo. Through Gigantopithecus may have eaten large amounts of bamboo, the phytolith evidence for bamboo consumption remains indirect, Ciocho says.

The researchers say other phytoliths found on these teeth belong to a family of tropical fruits common throughout Southeast Asia, suggesting that Gigantopithecus fed in forested areas. Regular consumption of the sugary fruits probably initiated the cavities observed in othe rGigantopithecus teeth, they add.

Phytoliths apparently dig into tooth enamel during chewing and create surface scratches, possibly bonding to the tooth through the combined action of friction and moisture, Ciochon says.

But if friction welds phytoliths onto tooth enamel, the resulting heat may also deform their shape, argues Lawrence Martin of the State University of New York at Stony Brook. "Phytolith research is potentially a major advance in dietary analysis," he says, "but there are no studies of how phytoliths bond to the tooth surface."

Silica bits in the soil more likely attached to the Gigantopithecus teeth after death, adds Frederick E. Grine of Stony Brook, who has studied microscopic wear on the extinct ape's teeth.

No one knows whether phytoliths routinely attach to the teeth of living animals, says Mark Teaford of Johns Hopkins University in Baltimore. Ciocho says he plans to look for phytoliths on the teeth of lemurs living on Madagascar, and hopes to obtain teeth of human acestors for phytolith analysis.