Flightless birds owe their success to the demise of the dinosaurs.
Credit: Wikimedia
SYDNEY: Large, flightless birds such as ostriches and emus, originated in the northern hemisphere, according to an Australian study that suggests they became grounded after dinosaurs went extinct.
Reconstructed migration patterns have raised questions about whether flightless birds could have their evolutionary origins in the planet's north.
Until now, most scientists thought these birds originated in the southern behemoth Gondwanaland, according to the study published in Systematic Biology.
Birds were no longer eaten by dinos
Matthew Phillips of the Australian National University and his team have also dismissed previous theories that asserted all large, flightless birds - or 'ratites' - share a flightless common ancestor.
Instead, they propose that species lost the ability to fly independently of one another at around the time dinosaurs became extinct, about 65 million years ago.
Without predation and competition from larger dinosaurs, some species of bird were able to shed the limitations flight imposes on body size and weight to evolve into the species of the order Struthioniformes, which includes ostriches, emus, cassowaries and kiwis.
Flightless birds fattened up
The removal of dinosaur predation and competition for food resources allowed ratites to remain grounded. "Birds tend to lose flight," says Phillips, "Particularly in island situations, unless it is crucial for finding food or escaping predators."
A glut of food would have allowed individuals to grow larger, and the lack of predators meant that there would no longer have been the need to fly away from danger.
These factors, along with the high-energy requirements of flight and of maintaining associated wing and pectoral apparatus could have led to the loss of flight altogether, say the researchers.
New genetic evidence, including DNA from the extinct giant moa of New Zealand, has shown that the common ancestor of ratites was a bird similar to today's tinamous, a native of South America that resembles a quail.
