How do scientists determine which animal a bone has come from? When it’s large or recent, the bone’s shape and DNA can usually provide enough information. But older bone fragments, like those often found around archaeological sites, are much harder to recognise.
Collagen – a protein found in bones, skin, hair, and teeth – can help. While the protein is present across all animal species, it’s changed slightly as each of those animals have evolved. This means that the chemical signature of collagen can be used to find the genus, and sometimes the species, of the owner of the bone.
“Traditionally zooarchaeologists – who are the archaeologists that study the remains of animals – use visual differences and the shape of bones and teeth to identify them,” explains Dr Tiina Manne, a zooarchaeologist at the University of Queensland.
“In Australia, a lot of the bone is quite fragmented, and because we have such high diversity of species, it can be really challenging to identify the taxa.”
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A technique called zooarchaeology by mass spectrometry – or ZooMS – is changing the field. By examining chemical differences in the collagen between animals, ZooMS “can really hone in”.
ZooMS works by taking a small fragment of collagen-containing tissue (as small as a milligram), dissolving it with enzymes and running it through a device called a mass spectrometer, which finds the weight of atoms and fragments of molecules.
This generates a “spectrum”, a chemical signature specific to the collagen of the original animal.
Spectra from known animals can be used to spot unfamiliar bones. “When you’ve got a good match, then you can say confidently that that’s what that animal is,” says Manne.
How precise can ZooMS get? “It relates back to how the animals diverged in the past,” says Manne. “If you’ve got a very high diversity of species […] you may end up just stopping at genus.”
It could spot the difference between an eastern grey kangaroo (Macropus giganteus) and a red kangaroo (Osphranter rufus), for instance, but not an eastern and a western grey (Macropus fuliginosus).
Manne is co-author on a paper in Royal Society Open Science, which has described the collagen signatures of 24 different Australian species.
The researchers used this data to identify turtle bones at a 19th century pearl-shell fishery on Barrow Island, in Western Australia. Bones from one species – the green sea turtle – were found at a spot that suggests they were being targeted for food by the Indigenous pearl divers who were forced to work on the island. “This further adds to the story of survival for indentured Aboriginal divers on Barrow Island,” write the researchers in their paper.
Manne says the reference spectra they’ve developed can be used to identify more animal bones around the country.
“This technique has really wonderful potential for getting more out of the past than we’re able to.”