No picky eater? CU team may turn tables on diet of early human relative

Jim Erickson, Rocky Mountain News

Friday, November 10, 2006

Paranthropus robustus was not a finicky eater.

That's the conclusion University of Colorado anthropologist Matt Sponheimer and his colleagues reached after using lasers to probe four fossil teeth from the extinct apelike creature, which walked upright across the African savannas more than a million years ago.

The findings may help overturn a long-held belief that Paranthropus, an early human relative, went extinct because it lacked a varied diet and therefore couldn't adapt to changing climatic conditions, Sponheimer said.

The results also raise questions about the importance that simple tools played in helping human ancestors diversify their diet and survive.

"This is some of the most exciting work in this field that I have seen in the last decade," said Frederick Grine, chairman of the anthropology department at Stony Brook University in New York, who was not involved in the study.

"It's one of those papers that when you read it you think, 'My God! I wish I'd done that myself,' " said anthropologist Bernard Wood of George Washington University.

The report appears in Friday's edition of the journal Science.

The study involved four molars from the jaws of Paranthropus robustus, which stood 4 feet tall, weighed less than 100 pounds, and had a brain slightly bigger than a chimpanzee's.

Between 2.4 million and 1.4 million years ago, our earliest stone-tool-making ancestors, Homo habilis and Homo erectus, shared the African savannas with Paranthropus.

The Homo branch of the family tree eventually led to modern humans. But Paranthropus went extinct between 1.4 million and 1 million years ago.

Conventional wisdom holds that the Paranthropus group perished as a result of its low-nutrient, high-fiber diet.

The animal's huge molars and massive jaw muscles seemed to support the idea that it fed mainly on small, hard, tough, fibrous plants, said Stanley Ambrose, of the University of Illinois.

According to the standard story, creatures in the Homo branch had a more varied diet and were better-equipped to deal with changes that began about 3 million years ago, when Africa's climate started getting drier and more seasonal. Stone tools gave our Homo ancestors access to new food types, including meat and bone marrow.

"This story has been around for more than 50 years, and it's hard to make people give up more than 50 years of preconceived notions," said Sponheimer, an assistant professor of anthropology.

"But it's almost impossible to square our results with the idea that Paranthropus was a true (dietary) specialist," he said. "This study may not put the nail in the coffin, but it's coming a lot closer to doing so."

The researchers found that Paranthropus had a diverse diet that included fruits, nuts, grasses, sedges, leaves, seeds and perhaps animals. And they apparently achieved that dietary diversity without tools.

"This is a pretty large sledgehammer blow into the wall of the hypothesis" that Paranthropus was a dietary specialist, Wood said.

The researchers used a technique called laser ablation to examine 1.8 million-year-old teeth pulled from Swartkrans Cave in South Africa.

The laser removed and vaporized bits of tooth enamel, which were then analyzed in a mass spectrometer to determine the ratio of rare carbon-13 to common carbon-12.

The carbon ratios revealed the types of foods the animals ingested.

And by probing different layers within a tooth, the scientists could determine what the animal ate in a given season or a particular year - like coring a tree to study its annual growth rings.

The team found that Paranthropus dramatically altered its diet over periods ranging from months to years.

Each tooth was sampled 10 to 17 times, and each sample removed a bit of enamel smaller than a grain of salt.

Over the past decade, researchers - including Sponheimer's co-authors at the University of Utah - have miniaturized and refined the laser technique so it inflicts little damage to precious fossil teeth.

"They are literally blazing a new trail to answers to fundamental questions about early (pre-human) paleoecology and evolution," Ambrose wrote in an accompanying Science article.

Because the improved laser ablation technique causes little damage, museum curators may be more likely to allow additional fossil studies of human ancestors and their relatives, Sponheimer said.

And the ability to observe short-term changes in diet could open the door to studies of migration and dispersal patterns, he said.

"These are questions we never really addressed in the past because they seemed more science fiction than science," Sponheimer said. "We're now making it something closer to reality."