A 176-year-old tortoise, believed by some to have been owned by Charles Darwin, has died at the Australian zoo owned by "Crocodile Hunter" Steve Irwin.

The giant tortoise, known as Harriet and pictured with Irwin and his wife Terri, was long reputed to have been one of three tortoises taken from the Galapagos Islands by Darwin on his historic 1835 voyage aboard the HMS Beagle.

Some scientists have cast doubt on the story, with DNA tests confirming Harriet's age but showing she came from an island that Darwin never visited.

TV star Irwin said he considered Harriet a member of the family.

"Harriet has been a huge chunk of the Irwin family's life," he said.

"She was possibly one of the oldest living creatures on the planet and her passing is not only a great loss for the world, but a sad day for my family. She was a grand old lady."