KEY POINTS:
New Zealand's kiwi and other flightless birds of the southern continents - African ostriches, Australian emus and cassowaries, and South American rheas - do not share a common flightless ancestor, an American researcher says.
Instead, in research published online by the National Academy of Sciences, University of Florida zoology Professor Edward Braun says each species individually lost its flight after diverging from ancestors that did have the ability to fly.
So some of the group, known as ratites, are more closely related to their airborne cousins than they are to other ratites.
And it means the ratites are products of parallel evolution - different species in significantly different environments following the exact same evolutionary course.
Prof Braun and his fellow researchers studied the ratites after a discovery made while working on a larger-scale project.
They were trying to understand the evolution of birds and their genomes by analysing DNA from the tissue of many different bird species to determine how they related to one another.
They found the ratites did not form a natural group based on their genetic make-up, but belonged to multiple related but distinct groups that contained another group of birds, the tinamous, with the ability to fly.
Previously, the ratites were used as a textbook example of vicariance, the geographical dispersal of a single species, resulting in two or more very similar sub-groups that can then undergo further evolutionary change and eventually become very distinct from one another. Scientists assumed that a single flightless common ancestor of the ratites lived on the supercontinent of Gondwana.
Now that is no longer assumed, Prof Braun wants to know why the birds evolved into such similar organisms in different environments.
- NZPA
