A hybrid giant tortoise, which contains the genetic footprint of Chelonoidis elephantopus, a species thought to have become extinct 150 years ago (PA/Yale University)
A giant tortoise which helped shape Darwin's ideas about evolution and was thought to have been extinct for 150 years may be living a secret life in the Galapagos Islands.
Genetic clues suggest pure-bred members of the species have recently interbred with some of their cousins.
Scientists found the genetic footprint of the species Chelonoidis elephantopus in the DNA of 84 tortoises from Isabela Island, part of the Galapagos island chain.
Each of these hybrids must have had a parent that was one of the missing species. In 30 cases, breeding had taken place within the last 15 years.
Since the lifespan of tortoises can exceed 100 years, there is a high chance that many C. elephantopus individuals are still alive, scientists believe.
"To our knowledge this is the first report of the rediscovery of a species by way of tracking the genetic footprints left in the genomes (genetic codes) of its hybrid offspring," said lead researcher Dr Ryan Garrick, from the University of Mississippi in the US.
The genetic evidence, reported in the journal Current Biology, suggests the tortoises inhabit the slopes of Wolf Volcano on Isabela Island, 200 miles from their ancestral home of Floreana Island.
During his historic voyage to the Galapagos in 1835, Charles Darwin noted that the shells of tortoises living on different islands had different shapes.
The shells of C. elephantopus on Floreana were saddle-shaped while tortoises on other islands had dome-shaped shells. It was partly this observation that inspired Darwin's theory of natural selection.
Not long after Darwin visited the Galapagos, C. elephantopus is thought to have been hunted into extinction by whalers and workers at a heating oil factory established on Floreana.