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.
Phillips and his team also found that the moa's closest living genetic relatives were the tinamous, rather than kiwis, emus or any other ratite as was previously thought.
Phillips' study examined mitochondrial DNA - short strands of DNA inherited only through the mother and not found in the nucleus - extracted from preserved moa birds, as well as from extant ratites and species of tinamous, and subjected the data to phylogenetic analyses.
Closest relatives are birds that fly
Molecular dating was carried out to determine the approximate points in time when each species began to diverge, and showed they must have had different ancestors.
Phillips and his team reconstructed possible migration patterns that could have allowed ratites to expand their ranges to include Africa, Antarctica, Australia, New Zealand and South America.
Until now, it was thought that all ratites ultimately stem from the southern super-continent Gondwana, which slowly broke up between 130 and 80 million years ago.
Flightless birds have origins in Europe
Further research is needed, but strong the theory already has some strong support, given that some of the earliest ratite fossils - dated at around 40 to 50 million years old - have been found in central Europe.
The fossils themselves were not considered sufficient evidence to rethink the origins of ratites, as they can be difficult to indisputably identify.
Trevor Worthy of the University of New South Wales, a palaeozoologist known for his research on the moa, says that although it is no surprise that ratites are not closely related to one another, confirmation that several species became flightless independently is an important development.
"Ratites aren't all closely related," he says. "People just assume that because they're all big and flightless; but in fact they haven't shared a common ancestor in 60 to 70 million years."
Worthy was also aware of the fossilised "flying ostriches in Eurasia," and was excited to discover more concrete evidence in favour of ostriches and other ratites having first emerged from the northern continents.
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