The study used molecular dating of the mitochondrial DNA from the moa, which stood 2.5 meters (6.7 feet) tall and weighed up to 250 kilograms (551 pounds), and found its closest relative to be the tinamous -- a flighted bird the size of quail, found in South America.Most of these had no natural predators or could run faster than the ones they did have until humans came on the scene.
Previously it was thought ratites all shared a common flightless ancestor about 80 million years ago and their worldwide dispersal occurred before the supercontinent of Gondwanaland broke up.
But Phillips says the problem with this theory was that much of the continental break-up occurred well before the proposed common ancestor.
Their study, which also included DNA sequencing of 22 bird species including flightless and flighted birds, shows ratites became flightless around 65 million years ago, he says.
This coincides with the extinction of dinosaurs in the Cretaceous-Tertiary event.
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