Scientists are now piecing together the truth about the giant racing tortoises of the Mascarene Islands in the Indian Ocean, which became extinct 200 years after the arrival in the 16th century of the deadliest predator of all: humans. Early accounts by explorers describe the animals, each about 2.5ft long, as being so plentiful that you "could walk for 300 yards on their backs without once touching the ground".
The arrival of the explorers spelt the end for a group of animals that were, by tortoise standards, turbo-charged. They had had millions of untroubled years in which they evolved paper-thin shells that left them up to 30kg (66lb) lighter, and much quicker, than their more conventional cousins.
They were not quick enough, however, to escape people, and the last racing tortoise was hunted and cooked in the early 1800s, ending perhaps 8 million years of an accidental experiment in evolution.
Because the islands - Mauritius, Reunion and Rodriguez - lie between 500 and 1,000 miles east of Madagascar, potential predators were never able to make the sea crossing.
In fact, said Dr Jeremy Austin of the Natural History Museum, DNA taken from bones suggests that all three islands were seeded by a single pregnant female ancestor, probably swept off an African beach by a big wave. "Tortoises can float rather like a coconut, and survive up to four months without eating or drinking anything," he told the British Association's Festival of Science in Cardiff yesterday.
"The first tortoise must have been wandering on a beach, suddenly found it couldn't touch anything with its feet, and then just bobbed along, and along, until it washed up on another beach."