An intact elephant bird egg is valued at £30,000-50,000 ($45,792-76,320) ahead of a natural history auction at Christie's London on October 8.
The elephant bird was a species of flightless bird that lived on Madagascar up until around the 14th to 17th centuries.
Intact elephant bird eggs are extremely rare
It stood at around 10 or 11 feet tall and weighed around 1,100 lbs. Their eggs are the largest known of any animal, including the dinosaurs.
They are believed to have been hunted to extinction by humans.
The extremely rare eggs are strongly in demand and regularly beat their estimates at auction. One specimen made £66,675 ($101,613) at Christie's London in 2013.
Other lots in the sale include a juvenile ichthyosaur fossil that carries an estimate of £25,000-35,000 ($38,160-53,424).
The lot was found in Lyme Regis, where the first specimen was uncovered in the early 19th century.
The auction house comments: "The first complete Ichthyosaur skeleton was found at Lyme Regis in 1811 by Mary Anning (of 'she sells sea-shells on the seashore' fame) .
"The order Ichthyosauria was introduced in 1840 by Sir Richard Owen, and today about 80 species are recognised."
Please sign up to our free newsletter to receive exciting news about unique items auctions.