A giant egg laid by an extinct elephant bird will be auctioned during Christie's Travel, Science, and Natural History Sale on April 24 this year in London. The value of the rare egg is estimated to be $45,000 but could sell for much more at the fine art auctioner's event. The egg is one foot in length and 9 inches in diameter. In the photos, you will see a size comparison between a chicken egg and this mammoth, which is about 100 times larger. Elephant birds went extinct several hundred years ago. They usually grew to be around 11-feet high.