Ritual or "payback" spearing killed an Australian Aboriginal man 4,000 years ago. But that's not all we know about him. Thanks to bone analysis by a University of Utah anthropologist, we also know what the victim ate.

Joan Brenner Coltrain, research associate professor, carried out isotope studies on skeletal samples from the man, whose remains were uncovered in a Sydney suburb in 2005. A report about the find was published in the British journal Antiquity in December 2007. It concludes that he is the earliest spearing victim known from Australia.

According to a press release by the Australian National University, Canberra, the skeleton was found in Narrabeen during excavations for gas works. Seventeen pieces of flaked stone, believed to be spear barbs, were found around or embedded in the skeleton, says the release.

Jo McDonald of the Australian National University, lead author of the Antiquities report, was quoted as saying archaeological evidence shows the man was killed and left in a coastal dune about 4,000 years ago.

"Ritual punishment using barbed death spears was witnessed at European contact in the Sydney region," the release quotes McDonald. "The Narrabeen man provides early archaeological evidence for ritual or payback killing by spearing."

Coltrain, an expert in isotope analysis, received bone samples from the skeleton at her laboratory in Salt Lake City. As she explained to the Deseret Morning News, the food that people or animals eat leaves its imprint in the molecular makeup of bones. It's most easily found in a pure state in collagen, which helps to give bone its structure.

Carbon-12 is common, an atom with six protons and six neutrons. Carbon-13 is an isotope with one extra neutron. She said C-13 is relatively rare, making up "only one percent of all global carbon — the carbon in your hair, tissues, etc." It is absorbed in nature at different rates by different types of animals or plants.

By examining the relationship of the isotope Carbon-13 to Carbon-12, scientists can tell whether the subject ate more seafood (or corn) vs. food obtained from land animals.

Also, the ratio of Nitrogen-15 to Nitrogen-14 in bone collagen allows a researcher to estimate how far up the food chain certain creatures were.

A sample may show a ratio that is relatively higher than average in the ratio of C-13 to C-12. That could mean a person ate seafood or maize, both of which have that sort of signature.

Also, if the sample has a lower than usual ratio of N-15 to N-14, that would indicate the food was lower on the chain, like plants; if higher, it indicates seafood like fish, which are higher on the food chain. By examining the fine print of the ratios, more details can be teased out of the samples.

Collagen is apt to be the best preserved and least contaminated material in bone samples, she said. It is from collagen, material that gives bones structure, that the carbon and nitrogen isotopes are extracted.

To examine the ratios, she first dissolves away the other bone protein using a weak acid, leaving the collagen. "If it's ancient bone, that collagen has to be decontaminated, so to speak, because it's been in the soil for a very long time."

That step is "like a detergent process. It gets cleaned up" chemically. "The collagen is demineralized and it's purified," Coltrain said, leaving material that retains isotopic signatures reflecting the person's diet.

The purified collagen is analyzed in a mass spectrometer, showing the ratio of the isotopes, which point to diet, she said.

Result: Coltrain's analysis showed the subject "subsisted on a diet of marine foods including fish, shellfish, seaweed and sea birds," says the release.

"I love what I do," the U. scientist said. "This Australian sample was wonderful and unique in its own way."

The report's authors are McDonald; Denise Donlon, Judith H. Field, Mark Rawson and Richard L.K. Fullagar, University of Sydney; Coltrain; and Peter Mitchell, Groundtruth Consulting of Gladesville, Australia.

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