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. Sotheby's will offer the egg at an auction on Thursday. It said it was estimated at 30,000 - 50,000 pounds( $ 76,410). In the 19th century they were greatly prized as sort of natural history curios by collectors, so a lot of them were collected then. But it's very rare to find them intact as this one is, they're often reassembled from broken parts. They're often found in remnants of fires from early settlers of Madagascar, which indicates they were probably used for food, which has contributed to the bird's extinction.