Flying before they couldn't fly: scientists reveal the past of ostriches and emus

Today, ostriches and emus do not fly, but a new study shows that their ancient ancestors were capable travellers, crossing vast distances by air.

Scientists have found that 56 million years ago they could fly long distances and that's how they spread across continents.

A team of international researchers, including Clara Widrig from the University of Oslo, published the work in the journal Biology Letters.

The scientists analysed a unique fossil specimen of the sternum of the ancient bird Lithornis promiscuus, found in the collections of the Smithsonian Institution. This bird was comparable in size to a modern heron.

After comparing the shape of the Lithornis sternum with more than 150 species of modern birds, the researchers found that it most closely resembled the bone structure of long-distance flying species such as herons and white ibises. This suggests that Lithornis was adapted to long flights, unlike modern non-flying ostriches, emus, casuars and kiwis.

This conclusion refutes an early theory that the ancestors of all modern flightless birds were originally incapable of flight and simply "spread" across different continents following the movement of the continents. However, genetic studies have shown that the separation of palaeognaths - the group to which they belong - occurred after the breakup of the supercontinent Pangaea. This means that the birds could only have travelled to South America, Africa, Australia and New Zealand by air.

Interestingly, flightless birds are not the result of a common evolutionary event, but an example of parallel evolution: different species independently gave up flying. The conditions under which this is possible are usually found on isolated islands, where there are no predators and food is easily accessible from the ground. But 50-60 million years ago, after the extinction of the dinosaurs, such conditions also existed on continents.

The researchers suggest that the extinction of predators after the catastrophe that wiped out the dinosaurs created a safe environment where birds could safely evolve on the ground. Lithornis also developed an olfactory apparatus that allowed it to efficiently search for food in the soil rather than in the crown of trees, further reducing the need for flight.