A giant semi-fossilised egg that is almost 100 times larger than a chicken's egg and still has the tiny skeleton of a bird inside is to go on sale for more than £50,000. The rare egg, which is 12 inches long and more than eight inches in diametre, belonged to the now extinct elephant bird that lived on Madagascar. The flightless birds, which stood nearly 10 feet (three metres) tall and weighted half a tonne, died out in the 17th century after heavy hunting. Scroll down for video . This 12 inch long elephant bird egg - just one of 25 known to remain intact around the world - is going on sale . There are thought to be just 25 preserved intact elephant bird eggs left in existence, with most in museums. Now one owned by a German marine biologist Professor Hubert Caspers, who worked at the Institute for Hydrobiology and Fisheries Science before his death in 1998, is to go on sale in Bruges, Belgium. Genetic material has been extracted from the shells of ancient elephant bird eggs. It has raised hopes that it may be possible to use cloning techniques to resurrect the extinct species. By injecting the genetic material into the unfertilised eggs of other large flightless birds like the ostrich, it may be possible to recreate the elephant bird. However, scientists face significant challenges that need to be overcome before this is possible. Cloning birds is considered to be particularly challenging. Extracting enough DNA from eggshells is also thought to be another limiting factor. Finally much of the habitat the the elephant birds once inhabited has now changed, so there may be few places where such a large species could now live. Scans taken of the egg, which is at least 400 years old, have also revealed the tiny bones of an embryo that had started to grow inside along with dehydrated organic material. Scientists were recently able to extract DNA from a similar egg, raising hopes that it may be possible to bring the elephant bird back to life using cloning techniques. Auctioneers Rob Michiels, who is selling the egg along with other items from Dr Caspers collection, said the egg appeared to be older than other eggs that have been sold recently. He said: 'The eggs of elephant birds are extremely rare - there are probably 25 of them in the world. 'This once comes from the collection of Dr Caspers and we have been asked to sell it by his children who thought it was a dinosaur egg. 'The children didn't know a lot about their father's collection. 'I was invited to Hamburg to look at a collection of antique tiles that he owned and I spotted the egg. It was just sat in a box. 'We have had a CT scan of the egg and it showed there is still organic, dehydrated material inside in the form of fetal bones. 'Technically, you could extract DNA from it and if you have a very large ostrich you could re-create a form of an elephant bird. 'The mother either ran away from the nest or was killed.' A CT scan of the elephant bird egg revealed dehydrated organic matter, shown as pink in the image above, and fragments of fetal bone still preserved inside the egg, shown by the small white mark in the pink material . The egg that has come up for sale (left) is one of the largest in the world and was laid by the now extinct elephant bird (right) which grew to around ten feet tall and lived in Madagascar until the 17th Century . The elephant bird, or Aepyornis maximus, was one of the largest birds to have ever lived. They are thought to have been common in Madagascar until they wre hunted into extinction during the 17th century. Fossilised egg fragments can still be found on the ground in some parts of Madagascar. David Attenborough, the natural history broadcaster, owns an almost complete eggshell that he pieced together from fragments collected by locals while he filmed Zoo Quest to Madagasar in 1961. The CT scans took slices through the egg and revealed dehydrated organic material and bone fragments inside . Another elephant bird egg was sold in 2013 for £66,675 - more than twice its expected value. Douglas G. D. Russell, senior curator of birds, eggs and nests at the Natural History Museum in London, said the elephant bird eggs were now very rare. He said: 'The export of their eggs from Madagascar is now strictly forbidden by the country’s legislation and complete eggs are relatively rare. 'As a rare, complete egg of an extinct species with some, albeit minimal, foetal bone it is noteworthy and all additional information on this enormous enigmatic bird is exciting.' Broadcaster David Attenborough is one of the few people to won a giant elephant bird egg after he pieced one together from fragments brought to him by locals while he was filming in Madagascar for the BBC in 1961 . This fossilised elephant bird egg, shown next to a hen's egg, sold for £66,000 during an auction in 2013 .
The egg, which belonged to a German biologist, has an eight inch diametre . CT scans have revealed dried organic material and bone fragments inside . It is thought to be one of only 25 intact elephant bird eggs left in the world . The egg is expected to sell for more than £50,000 at an auction in Belgium . Elephant birds died out during the 17th century after being heavily hunted .