New theory on the origin of flightless birds

New DNA studies by Royal Ontario Museum (ROM) researchers indicate that two opposing views on the origin of ratites, large flightless birds originating on the southern supercontinent Gondwana, might both be correct.

Allan Baker, Vice President/Senior Curator (Ornithology) Natural History Department with Dinornis robustus or the “South Island Giant” [Credit: Oliver Haddrath]

Dr. Allan J. Baker, Head of the ROM’s Department of Natural History and Oliver Haddrath, Research Technician, Ornithology Division, Department of Natural History at the ROM, studied the ancient DNA of New Zealand moas (extinct flightless birds), using molecular dating. The study showed that three of the ratite lineages diverged at around the same time as the northern and southern continents fragmented, however, two of the lineages had subsequently flown to the continents they now live on.

This study provides important evidence to the ongoing controversial debate on whether or not flightless birds, such as the ostrich, emu, cassowary, kiwi, rhea or the extinct moa and elephant bird, are descended from a once flying ancestor. Charles Darwin thought that these ratites probably flew to the southern continents where they can be found today and later independently lost their power of flight. However, morphologists have argued that the common ancestor to these birds was already flightless.

They believe that instead of flying to the southern continents, ratites likely floated on continental fragments as Gondwana broke apart.

Past DNA studies have supported Darwin’s hypothesis. The flying tinamou of South America was found to be most closely related by DNA to the flightless giant moa of New Zealand, meaning the common ancestor was most likely a flying bird, as Darwin had supposed.

Through molecular dating, Baker and Haddrath were also able to date the origin of modern birds to the early Cretaceous Period, which is much earlier than the oldest fossils of modern birds that have been discovered to date. Further research into unexplored places such as Antarctica or sites where much older fossils have yet to be discovered might provide further insight into why both theories may be able to coexist. 

Source: Royal Ontario Museum [October 22, 2012]