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 30-centimetre long, 23-centimetre diameter egg fetched £66,675 ($104,475). It had been valued at £20,000 to £30,000 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 3½ metres. Christie's says their eggs are 100 times the size of an average chicken's.