Bones of giant birds pose mating mystery

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The Independent Online

A study of the fossilised bones of a giant bird which died out about 800 years ago has revealed that the female was three times the size of the male.

Scientists discovered that the largest giant moa birds were not a separate species, as originally thought, but an extreme example of sexual dimorphism. A study of the DNA extracted from the bones of large and small moas revealed that the females were huge, weighing up to 250kg and standing up to three metres tall. The males were puny, weighing as little as 60kg, and were about one metre tall.

This raises the question of how the moa cocks were able to mate with their huge hens.

Professor Alan Cooper, director of Oxford University's Ancient Biomolecules Centre, said the findings were unexpected because it was widely thought that large, small and medium-sized moa belonged to separate species that did not interbreed.

He said: "Such a large difference between the sexes has never been seen before, and consequently nobody considered that these different groups of bones could actually belong to the same species. It raises concerns about the logistics of mating - but in the emu for example, the female sits during mating. If this was the case with the moa, it would have looked like a horse and jockey."

The study, published today in the journal Nature, analysed DNA extracted from the bones of moa that lived in swamps and caves in New Zealand. Moa died out after the arrival of the Maori, around AD1100, who hunted the birds to extinction.

Professor Cooper said: "When we examined genes that evolve very rapidly we could find no consistent differences between tiny and giant [moa] specimens. When we looked at sex-linked genes all the medium and giant individuals showed up as femaleswhile the males were the little ones."

It is the first time that scientists have identified the sex of an extinct animal using DNA.