The Buffalo Museum of Science has discovered a true treasure in its collection, mislabelled for years as a model due to human error. The discovery is an intact elephant bird egg. The extinct elephant bird (Aepyornis maximus) was not just one of the largest birds ever to live, it also laid eggs larger than almost any dinosaur, let alone modern birds.

Elephant birds roamed the forests of Madagascar until about 800 years ago. The name covers seven species related to modern emus and cassowaries, although their closest living relatives are kiwis. As the name suggests, the largest of these, indeed a contender for the largest ever bird was Aepyornis maximus, growing up to 3 meters (9.8 feet) high and weighing as much as 500 kilograms (1,100 pounds).

Elephant birds in general, but A. maximus in particular, laid enormous eggs – the largest known specimen being 33 centimeters (13 inches) long. Human consumption of these eggs may well have caused their extinction – they had a volume similar to 150 chicken eggs – and even centuries after they were gone travelers reported the Malagasy people using elephant bird eggshells as bowls. Today the eggs are so highly valued David Attenborough made a documentary just on the quest to find them, and the egg he glued together from shattered pieces.

Therefore, the museum is understandably thrilled to discover one in its collection. Records indicate it was purchased in 1939 and filed as a model for display to give visitors a sense of how large these eggs were. Generations of staff accepted this, but on conducting a check of their collection, Paige Langle, collections manager of zoology, thought the specimen was just a little too realistic in its weight and surface texture.

Langle also found an actual model, which was far less convincing. Radiographing the semi-fossilized egg confirmed it was not only real, but had been fertilized and contained fragments of a partially developed bird. The results confirmed the museum has one of just 40 intact elephant bird eggs held by public institutions. Astonishingly, two of these rare objects were found in dunes in Western Australia, apparently having floated across the Indian Ocean.

“Lost, hidden or misidentified artifacts and specimens are not uncommon in museums that have been collecting for centuries, and we are thrilled to rediscover this rare egg in our collection,” Buffalo Museum's Director of Collections, Kathryn Leacock, told local news outlet WKBW Buffalo.

This egg is not quite the largest elephant bird egg ever found, but at 30 centimeters (12 inches) long and 70 centimeters (28 inches) in circumference, it is still among the largest eggs ever found – weighing almost 1.5 kilograms (3 pounds).

The egg will go on display from May 1. No one tell Daenerys Targaryen.