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Across the globe, there are around 40 species of birds that are incapable of flying.

For centuries, ornithologists have wondered how and why these species lost their flying skills and developed different bone structures to their flying counterparts.

Now, by tracing the lineage of a particular ground-dwelling bird in South America, scientists believe a number of these birds may have flown to different continents before evolving independently from each other. 

By tracing the lineage of the ground-dwelling tinamou bird in South America, pictured, scientists believe a number of flightless birds, known as ratites, descended from flying ancestors and may have flown to different continents before evolving independently from the rest of the group

Ostriches, emus, rheas, and kiwis are large flightless birds collectively known as ratites.

They differ from birds that fly because they have flat breastbones, smaller wings and reptile-style bones in their mouth.

This means they don't have the muscles or the wingspan to leave the ground, compared to flying birds.

However, the ground-dwelling tinamou is an exception, and doesn't fit in neatly to either group.

The South American bird has the palate bones of the ratites, but the sternums of flying birds - and can fly if it needs to.

To discover where the tinamou fits in the evolutionary history of flightless birds, Canadian Allan Baker analysed almost 1,500 DNA segments from tinamous, emus, ostriches and the extinct moas.

He extracted the sequence of the moa from a toe bone and compared this DNA to the other specieis using computer models to simulate different evolutionary changes.

To discover where the tinamou fits in the evolutionary history of flightless birds, Canadian Allan Baker analysed DNA segments from tinamous, emus, ostriches and the extinct moas, illustration pictured. He extracted the sequence of the moa from a toe bone to discover it was closely related to the tinamou

Ostriches, emus, pictured, rheas, and kiwis are large flightless birds collectively known as ratites

According to the results, Baker said the tinamou evolved within ratites, and confirmed it is closely related to moas, which lived in New Zealand around 1400 AD.

Baker continued that all ratites, including tinamous, must have therefore once had ancestors that were able to fly. 

Tinamous maintained this ability, while the other lineages each lost flight independently.

Previous research suggested that the flightless birds ended up on different continents when the Pangea's southern section separated 100 million years ago.

However, Baker's findings suggest the ratites evolved into separate lineages between 90 and 70 million years ago, while the tinamous and moas diverged around 30 million years later.

This new research suggests they could have flown to new lands and evolved independently from one another and, as Baker claims, puts the debate about flightless birds 'to rest.'

The findings are published in the journal Molecular Biology and Evolution.