It may be a curlew or a kakapo. It may be the baiji, or a bat. But no one knows for sure, now, what is the rarest creature on the planet.
For the title is going begging this week, after the death of Lonesome George, a giant tortoise from the Galapagos Islands who was the last remaining member of his subspecies.
George was thought to be about 100 years old – which makes his death tragically premature, as giant tortoises are thought to live to about 200.
He was from Pinta island, and there are no more members of the Pinta subspecies of the giant tortoise to be found anywhere.
Indeed, scientists believed that Chelonoidis nigra abingdoni had become extinct until George was discovered on Pinta in 1972.
Subsequently, he became part of the Galapagos National Park tortoise breeding programme and was encouraged to mate with females of a closely related subspecies but never succeeded in reproducing.
National Park officials said George was found dead in his corral by his keeper, Fausto Llerena, who had looked after him for 40 years.
Lonesome George became a tourist symbol of the Galapagos, the Pacific archipelago visited by Charles Darwin in 1835 which receives 180,000 visitors a year.