Sydney, January 26 (ANI): A new study has suggested that the flighted ancestor of birds such as the Australian emu and cassowary became too heavy to fly after the extinction of dinosaurs made it safer to forage for food.
According to a report by ABC News, the finding by Australian National University (ANU) biologist Dr Matthew Phillips and colleagues at Massey University in New Zealand, follows on from recent work that raised uncertainty about the "single ancestor" theory of the group of flightless birds, known as ratites.
Ratites are a group of flightless birds that include the Australian emu and cassowary, African ostrich, New Zealand's kiwi and now-extinct moa, rhea from South America and the extinct elephant birds of Madagascar.
The study used molecular dating of the mitochondrial DNA from the moa, which stood 2.5 metres tall and weighed up to 250 kilograms, and found its closest relative to be the tinamous - a flighted bird the size of quail, found in South America.
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, according to Phillips, the problem with this theory was that much of the continental break-up occurred well before the proposed common ancestor.
The study, which also included DNA sequencing of 22 bird species including flightless and flighted birds, shows ratites became flightless around 65 million years ago.
This coincides with the extinction of dinosaurs in the Cretaceous-Tertiary event.
"Our study suggests that the flighted ancestors of ratites appear to have been ground-feeding birds that ran well," said Phillips.
"In the absence of predators and with abundant food resources on the ground, there is a tendency for birds to evolve larger size and become flightless," he added.
"Larger ground-feeding birds can be more efficient at turning food into growth and reproduction, but with size increase, comes the cost of flight becoming less efficient," he said. (ANI)