Long-held assumptions of flightless bird evolution challenged

Washington, September 4 : A new research has indicated that large flightless birds of the southern continents do not share a common flightless ancestor as once believed, thus challenging long-held assumptions of flightless bird evolution.

The research, conducted in part by University of Florida zoology professor Edward Braun, determines that birds like African ostriches, Australian emus and cassowaries, South American rheas and the New Zealand kiwi, don't share a common ancestor as was once believed.

Instead, each species individually lost its flight after diverging from ancestors that did have the ability to fly.

The new research, which appears in the online edition of the Proceedings of the National Academy of Sciences, has several important implications.

First, it means some ratites, like the emus, are much more closely related to their airborne cousins, the tinamous, than they are to other ratites, according to Braun.

Second, it means the ratites are products of parallel evolution - different species in significantly different environments following the exact same evolutionary course.

Braun and his fellow researchers began closely studying this group of flightless birds, known collectively as ratites, after a discovery made while working on a larger-scale effort to better understand the evolution of birds and their genomes by analyzing corresponding genetic material sampled from the tissue of many different bird species and determining how they relate to one another.

As they analyzed the genetic material, they noticed that the ratites did not form a natural group based on their genetic makeup.

Rather, they belonged to multiple related but distinct groups that contained another group of birds, the tinamous, with the ability to fly.

Scientists has earlier assumed that a single flightless common ancestor of the ratites lived on the supercontinent of Gondwana, which slowly broke up into Africa, South America, Australia and New Zealand.

"Once divided, the ancestor species evolved slightly in each new location to produce the differences among the present-day ratites," Braun said.

But in light of this new information, Braun said that it's more likely that the ratites' ancestors distributed themselves among the southern continents after the breakup of Gondwana, which began about 167 million years ago, in a much more obvious way.

As to why did these birds evolve into such similar organisms in such different environments, Braun said, "To know for sure, we'll have to go into the lab and really study the genetics underlying the ratites' developmental pathway."

ANI