The Galapagos Island reptile was the last of the Pinta island giant tortoise subspecies and he was found dead in his pen on Sunday.
He had become an ambassador of sorts for the archipelago off Ecuador's coast whose unique flora and fauna helped inspire Charles Darwin's ideas on evolution.
Galapagos conservation official Washington Llerena says scientists suspect Lonesome George died of a heart attack. His was believed to be about 100 years old, not especially old for a giant tortoise.
Scientists from the U.S. were aiding in the autopsy by videoconference.