Tuesday, September 8, 1998 Published at 12:07 GMT 13:07 UK
DNA clues to tortoise extinction
Most tortoises are heavyand sluggish
British scientists have extracted DNA from giant land tortoises that became extinct 400 years ago when humans colonised their Indian Ocean islands.
The scientists from the Natural History Museum in London said their breakthrough could answer questions about the evolution of the unique fleet-footed giant tortoises and explain why they died out.
"Ancient DNA studies have used only one or two species. Never before has ancient DNA been used to unlock the secrets of evolution in a completely extinct group of animals," said the scientists.
The DNA was recovered from bones found in caves on the islands.
The scientists ground the bones to a fine powder before extracting the DNA and analysing it with highly sensitive techniques.
Sleek and fast
Unlike their Galapagos Island cousins, which are heavy and sluggish, the Mascarene giant tortoises had thin shells with big openings for the legs and head.
Describing the animals at the British Association festival of science at Cardiff University, Dr Jeremy Austin said: "This would have reduced the weight of the shell enormously, leading to the possibility that these animals were the world's only "lightweight, racing tortoise".
The tortoises evolved this way because there were no large predators to threaten them until the arrival of man in the early 1600s.
They were hunted for food and attacked by introduced predators such as dogs, so that by the early 1800s all the native Mascarene tortoises were extinct.
Dr Austin said there were many unanswered questions about the tortoises' evolution.
The scientists are using fragments of DNA to trace the evolutionary path of the tortoises.
Dr Austin said: "These results _ are allowing us to understand for the first time the origins and evolutionary history of this unique group of tortoises."