An intact elephant bird egg is to cross the block at Christie's London with a valuation of £40,000-60,000 ($59,280-88,920).
The elephant bird was native to Madagascar and died out sometime between the 14th and 17th centuries.
It's unknown what caused this, but it's probable they were hunted to extinction by humans.
Christie's comments: "The Elephant Bird was thought to be the giant flying beast known as the Roc (or Ruhk) in the tales of Sinbad and accounts of Marco Polo's voyages.
"The bird grew to around 10 or 11 feet in height and whilst probably unable to devour an elephant, as the Roc was reputed to do, it certainly was the largest bird ever to have lived."
The egg itself stands at 12 inches tall. It will form part of Christie's April 23 travel, science and natural history auction.
They are highly sought after among collectors, with one specimen selling for £66,675 ($101,613) at Christie's in 2013.
The fossilised skull and neck of a Plesiosaur is likely to prove another highlight, with a valuation of £20,000-30,000 ($29,640-44,460).
The lot dates to the late Cretaceous period (100.5m-66m years ago) - around the time dinosaurs were wiped out by a comet.
Please sign up to our free newsletter to receive exciting news about auctions of unique items.