Lonesome George, a giant tortoise who was the last of his kind, has died on the Galapagos Islands.
The Galapagos National Park confirmed the reptile was found dead in his corral by his long-time keeper Fausto Llerena.
He lived at a tortoise breeding centre on the archipelago's island of Santa Cruz and was discovered on Sunday morning in his pen.
A spokesman said the tortoise, who is believed to have been around 100 years old, had died of unknown causes.
Scientists had expected him to live another few decades at least.
Lonesome George was found in 1972 and had become a symbol of Ecuador's Galapagos Islands, which attracted some 180,000 visitors last year.
He was the last member of a species of giant tortoise from La Pinta, one of the smallest islands in the Galapagos. With no offspring and no other known survivors of his species, he was considered the rarest creature in the world.
The giant Galapagos tortoises, which can live up to 200 years old, were among the species that helped Charles Darwin formulate his theory of evolution in the 19th century.
The Galapagos National Park will carry out a necroscopy to determine the cause of death and is considering embalming George's body so that it can be displayed in the park.
Scientists had been trying unsuccessfully to get George to mate since 1993.
The Pinta Island species of tortoise had been declared extinct but in December 1971, a scientist studying snails spotted a lone tortoise on the island.
A search was launched and the following year, National Park wardens located the male who went on to be named Lonesome George.
Various mates were provided for him after the discovery but attempts to keep his sub-species alive failed.
Two female tortoises from Wolf Volcano lived with him but the eggs produced were infertile. Then two females from Spanish island's tortoise population, the species most closely related to Pinta tortoises, were placed with him last year.
Tortoises were numerous on the islands until the late 19th century when humans arrived and hunted them for their meat. They also suffered when goats were introduced to the area.
But a recovery program run by the park and the Charles Darwin Foundation has increased the overall population from 3,000 in 1974 to 20,000 today.