

By using kangaroo fossils as archaeological biosensors, scientists could help solve one of Australia's enduring mysteries.

Aborigines arrived 45,000 years ago, spreading across the continent with startling rapidity. Then, in anthropological terms, they cooled their heels for the next 40,000 years: no significant population expansion. No fundamental changes in lifestyle.

That changed 5,000 years ago. Populations shot up. Settlements increased in number, and their inhabitants grew more sedentary. Scientists can't explain it.

"What's going on? Why change then? There's no obvious environmental or ecological correlate. There's no climate change," said Doug Bird, a Stanford University anthropologist who's helped devise an ingenious investigative workaround: kangaroo fossil analysis.

Bird's team recently published a study on "fire stick farming," a traditional method of ecosystem management still used by aborigines in Australia's Western Desert. Burning old-growth spinifex grass makes it easier to hunt lizards; cookpot-friendly kangaroos and emus fatten themselves on grasses flourishing on newly cleared lands.

Fire stick farming is too small-scale and subtle to leave behind the sort of landmarks that have made prehistoric terraforming relatively easy to spot elsewhere, said Bird, and charcoal deposits will be too mixed to interpret. But human-directed changes in foliage should leave telltale traces in the bones of kangaroos, which have small, stable home ranges and versatile dietary habits.

"If you get a shift from woody-like vegetation to grasses, it should be indicated in the shift of stable isotopes of nitrogen and oxygen" in kangaroo bones, said Bird.

Combine that analysis with carbon-14 dating, said Bird, and researchers could make a time-and-space map of aboriginal settlement and migration. This could help scientists figure out what caused such massive upheavals in a culture that had been stable for 40,000 years.

Bird cautioned that the method is still experimental. His team is now calibrating the methodology by analyzing kangaroo fossils from recent burn sites.

"It's completely untested. It might not work," he said. "But if it does, that'd be cool."

The ‘‘fire stick farming’’ hypothesis: Australian Aboriginal foraging strategies, biodiversity, and anthropogenic fire mosaics [Proceedings of the National Academy of Sciences]

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Images: Vegetation mosaics created by fire stick farming, from PNAS; a kangaroo, from travelingtamas.*

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