Humongous extinct bird egg up for auction. Where did it come from?

Larger than a rugby ball and several hundred years old, a giant, partly fossilized egg laid by an extinct bird is set to be auctioned by Christie's. The auction house expects the egg to fetch up to $45,000.

James Hyslop, the Christie's scientific specialist shown in the Magritte-esque photo above, told the BBC that the type of egg is "the largest egg ever laid by any animal."

The egg is "bigger than dinosaur eggs," said Hyslop.

Of course, phylogenetically speaking, birds are dinosaurs, a fact that is easier to believe when you consider the creature that dropped this particular ovum, the elephant bird.

The elephant bird, if you haven't guessed by its name and the size of the egg, was big. Bigger, in fact, than the biggest living bird, the African ostrich. Like the African ostrich, the elephant bird was flightless and from Africa – Madagascar to be exact. But unlike the African ostrich, it stood over 10 feet tall and weighed up to 800 lbs. In short, it's not the sort of creature you'd like to meet in a dark alley, unless you happen to be a paleoornithologist with a tranquilizer rifle.

Elephant birds, a term that comprises up to four species, were common on Madagascar through the 17th century. They are thought to have been driven out of existence by humans, either directly through hunting or indirectly through diseases carried by poultry brought to the island.

How did the elephant bird get so big? It's an example of island gigantism, a phenomenon by which animals on islands tend to evolve to be much larger than their mainland counterparts. Island gigantism often occurs when islands make poor habitats for large predatory mammals, either because they offer limited ranges or because the mammals can't cross the water to get there in the first place. In the absence of such predators, other animals can evolve to fill their niches. Either that, or the lack of predators allow them to grow larger, because there is no need to hide or escape. But when humans arrive on an island, its giants tend to go extinct.  

Examples of island gigantism can be found with Komodo dragons, Galapagos tortoises, and the Flores giant rat.  

In 1894, the science fiction author H.G. Wells published a short story about a man who discovers an ancient elephant bird egg, which subsequently hatches.