Plaque unlocks ancient Rapa Nui diet

Transcript

A study of plaque from ancient teeth is believed to have provided more insight into what plants the people of Rapa Nui relied on before European contact.

Monica Tromp, from New Zealand's Otago University, and John Dudgeon, from Idaho State University, say their research clears up a previous finding that palm trees may have been a staple plant for many centuries.

Ms Tromp says the analysis, published in the Journal of Archaeological Science, was consistent with the modern sweet potato.

MONICA TROMP: We weren't surprised to find sweet potato but we were surprised that we found it in all of the samples that we looked at except for a couple of them. The samples should represent around between 13 AD and

JAMIE TAHANA: You say you were surprised it was so prevailing. What was the surprising element there?

MT: There was a lot of debate about when sweet potato was introduced because it was introduced from South America but we are not sure when it was introduced but this research it looks like it was probably introduced before early Polynesians spread out to Easter Island, New Zealand and Hawaii.

JT: And what's significant about this finding?

MT: That it was earlier than thought, because a lot of people thought there might have been multiple migrations to places or that sweet potato could have been a later introduction and it looks like it could have been an earlier introduction.

JT: This was the second lot of research you've done on the sweet potato theory, you went a first time and weren't happy with what you found, or something, there?

MT: The first time I looked at the calculus I found I was only looking a phytoliths, which are made out of silica and they're little plant skeletons that are found in most plants, but not all plants. And all I was finding was some thousands of them from palm trees and palm trees should have been extinct on the island within the first couple of hundred of years that people were there and because we think these teeth span much longer than when the trees were there we were confused and thought that maybe the trees had persisted, but all the other evidence on the island shows that the trees were gone and so we weren't quite sure what to make of it and so we waited to publish our results until we had a chance to look at the starch as well.

JT: To discover this, what was the process?

MT: I went to a conference and I saw a presentation that was kind of a eureka moment for me, I saw that they had found these phytoliths - these little plant skeletons - embedded into the skins of tubers that had been growing in the sediment. And so as the tubers were growing down into the sediment they were picking up things from the dirt around them and so I immediately thought 'oh, that could be an explanation for why we're finding so much palm,' because the island used to be covered in palm and so all the remains of the palm trees are in the sediment - all these phytoliths - and so as the sweet potatoes are growing into the ground they're picking up all of these little bits of dirt and plant remains and incorporating them into their skins and then when people were eating them they were getting stuck into their teeth.

JT: As part of this research you examined the dental plaque from these historical teeth?

MT: Yes, yep.

JT: What's the process behind that?

MT: You scrape it off the teeth, so it's a bit like you're being a dental hygienist for the dead, and it doesn't harm the teeth or anything so you take that off and you extract the micro-fossils. So you essentially are decalcifying this hardened plaque on the teeth and are releasing all the little bits that are inside of it. There's been a lot of research recently that's also found proteins and DNA and calculus. So it's kind of a little treasure trove of data for archaeologists.