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No match for mankind


 
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Dr Arthur White unravels the mystery of ancient turtle bones found on an island in Vanuatu.
A few years ago, on the island of Efate in Vanuatu, the local villagers wanted to construct a prawn farm by excavating an old exposed reef platform and create a shallow embayment that would contain the captive prawns. As soon as earth digging started human bones were uncovered and so a group of anthropologists from the Australian National University were invited to go to the site.
The bones were obviously not recent as they were embedded in the reef platform and it turned out that they were from a group of people known as the Lapita people who were the first people to colonise the western Pacific. They were known, unusually for islanders, for their pottery and the distinctive markings on them. The dig certainly uncovered pottery as well as a cemetery.

 
The dating of these skeletons showed that they were 3,300 years old.
Since Vanuatu lies in an unstable area of the Pacific, the anthropologists decided to dig a soil trench to see what other information could be dug up. What they uncovered was a midden which had expected shells along with fish and animal bones in the upper level. At the bottom level they uncovered large bones, which resembled turtle bones although they were different. The bones from the upper and lower levels were sent to Dr White for identification. The bones in the upper levels proved to be marine turtles but the bones in the lower level were definitely not. They were land-based turtles and turned out to be from the family of horned turtles, well documented in Australian fossil records as far back as 50 million years ago. These turtles were widespread in Australia’s east and north, diversifying in forms and evolving into gigantic forms by Pleistocene times some two million years ago.

 
By the middle of the Pleistocene, however, the turtles started to die out on mainland Australia and were soon confined to the extreme east coast.
At about the same time they started turning up on offshore Pacific islands, which was curious because they were not swimmers. Studies of another land turtle from the Aldabran group of islands in the Indian Ocean showed that these large land turtles could float to other islands on the prevailing sea currents. It seems that horned turtle did the same as there are remains from Lord Howe Island, the Solomon Islands and Fiji.

 
What was special about the Vanuatu midden was that it was evidence of human contact with these land-based turtles.
The Lapita people obviously hunted these turtles and investigating the midden from the bottom up showed that there were no turtle bones at about 2,900 years ago, their extinction on Vanuatu taking only 400 years. Land-based island species are very susceptible to human predators as they have no escape and these slow creatures were no match for the hunters.

 

 
It is hoped that now DNA samples can be gained from the turtle bones to try and help unravel the mystery of the kinship of horned turtles compared to others.

All images from Arthur White
Text: V.B. June 2010


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