LONDON -- A massive, partly fossilized egg laid by a now-extinct elephant bird has sold for more than double its estimate at a London auction.

Christie's auction house said Wednesday that the foot-long, nearly nine-inches in diameter egg fetched 66,675 pounds ($101,813). It had been valued at 20,000 to 30,000 pounds pre-sale, and was sold to an anonymous buyer over the telephone after about 10 minutes of competitive bidding.

Elephant birds were wiped out several hundred years ago. The oversized ovum, laid on the island of Madagascar, is believed to date back before the 17th century.

Flightless, fruit-gobbling elephant birds resembled giant ostriches and could grow to be 11 feet high (3.4 meters). Christie's says their eggs are 100 times the size of an average chicken's.

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  • An employee of Christie's auction house poses with a complete sub-fossilised Elephant Bird egg (R) and a chicken's egg (L) in London on March 27, 2013 during a press preview of their April 'Travel, Science and Natural History' sale. This pre-17th century egg of the extinct Elephant Bird, the largest bird ever to have lived, is approximately 100 times larger than the average chicken's egg and is estimated to fetch 20,000 - 30,000 GBP when it goes on sale on April 24, 2013. (JUSTIN TALLIS/AFP/Getty Images)

  • An employee at Christie's auction house examines a complete sub-fossilised elephant bird egg on March 27, 2013 in London, England. The elephant bird egg is expected to fetch 30,000 GBP when it features in Christie's 'Travel, Science and Natural History' sale, which is to be held on April 24, 2013 in London. (Photo by Oli Scarff/Getty Images)

  • An employee at Christie's auction house examines a complete sub-fossilised elephant bird egg, next to a chicken's egg, on March 27, 2013 in London, England. The elephant bird egg is expected to fetch 30,000 GBP when it features in Christie's 'Travel, Science and Natural History' sale, which is to be held on April 24, 2013 in London. (Photo by Oli Scarff/Getty Images)

  • Alexander, aged 1, and his mother admire a complete sub-fossilised elephant bird egg at Christie's auction house on March 27, 2013 in London, England. The elephant bird egg is expected to fetch 30,000 GBP when it features in Christie's 'Travel, Science and Natural History' sale, which is to be held on April 24, 2013 in London. (Photo by Oli Scarff/Getty Images)

  • James Hyslop, a Scientific Specialist at Christie's auction house examines a complete sub-fossilised elephant bird egg, next to a chicken's egg, on March 27, 2013 in London, England. The elephant bird egg is expected to fetch 30,000 GBP when it features in Christie's 'Travel, Science and Natural History' sale, which is to be held on April 24, 2013 in London. (Photo by Oli Scarff/Getty Images)

  • An employee at Christie's auction house examines a complete sub-fossilised elephant bird egg on March 27, 2013 in London, England. The elephant bird egg is expected to fetch 30,000 GBP when it features in Christie's 'Travel, Science and Natural History' sale, which is to be held on April 24, 2013 in London. (Photo by Oli Scarff/Getty Images)

  • A chicken egg is displayed next to a sub-fossilised pre-17th century Elephant Bird egg to scale the size difference at Christie's auction house's premises in London, Wednesday, March 27, 2013. The Elephant Bird egg, which is estimated to fetch 20,000 to 30,000 pounds ($30,210 to $45,315 and 23,645 to 35,467 euro) in the forthcoming Travel, Science and Natural History sale on April 24, measures over 100 times the average size of a chicken egg, and stands at 21cm in diameter and 30cm in height. The extinct Elephant Bird species was native to Madagascar and among the heaviest known birds. (AP Photo/Matt Dunham)

  • Alexander Robinson, aged 16 months, is held up by his mother Alexandra to be photographed next to a sub-fossilised pre-17th century Elephant Bird egg at the auction house's premises in London, Wednesday, March 27, 2013. The Elephant Bird egg, which is estimated to fetch 20,000 to 30,000 pounds ($30,210 to $45,315 and 23,645 to 35,467 euro) in the forthcoming Travel, Science and Natural History sale on April 24, measures over 100 times the average size of a chicken egg, and stands at 21cm in diameter and 30cm in height. The extinct Elephant Bird species was native to Madagascar and among the heaviest known birds. (AP Photo/Matt Dunham)

  • In this Wednesday, March 27, 2013 file photo, Christie's scientific specialist James Hyslop poses for photographs with a sub-fossilized pre-17th century Elephant Bird egg at the auction house's premises in London. A massive partly fossilized egg laid by a now-extinct elephant bird has sold for more than double its estimate at a London auction. Christie’s auction house said Wednesday, April 24, 2013, the foot long, nearly nine-inches in diameter egg fetched 66,675 pounds ($101,813). It had been valued at 20,000 to 30,000 pounds pre-sale, and was sold to an anonymous buyer over the telephone after about ten minutes of competitive bidding. (AP Photo/Matt Dunham, File)