Galapagos National Park/AP Photo

The giant tortoise known as Lonesome George died Sunday, according to officials at the Galapagos National Park in Ecuador.

He was found Sunday morning in his pen by his longtime keeper, Fausto Llerena, the park said in a statement. Lonesome George was the last remaining tortoise of its kind and was estimated to be about 100 years old. Despite what seems like old age for humans, scientists had expected him to live a few more decades.

Lonesome George was found on Pinta Island in 1972, although Pinta tortoises were believed to be extinct. In an attempt to keep the species alive, mates had been provided for Lonesome George. All mating attempts failed, and the tortoise continued to live at a breeding center on the island of Santa Cruz in Ecuador. Lonesome George became a symbol of Ecuador's Galapagos Islands.

"The plight of Lonesome George provided a catalyst for an extraordinary effort by the government of Ecuador to restore not only tortoise populations throughout the archipelago but also improve the status of other endangered and threatened species," according to the statement posted on the park's website.

The park said the cause of death will be investigated.

The Associated Press contributed to this report.