The mystery of how related flightless birds ended up so far apart on different continents may have been solved.
Ostriches in Africa, emus in Australia, rheas in South America, and other large, flightless birds live on continents separated by vast oceans. For decades, scientists puzzled over how these related birds managed to spread so widely without the ability to fly.
One early explanation suggested their ancestors simply walked across land when Earth’s continents were fused into the supercontinent Pangaea. But the timeline doesn’t fit: Pangaea split apart about 195 million years ago, while genetic studies show the common ancestor of today’s paleognaths lived only ~80 million years ago.
To solve this mystery, researchers turned to an exceptionally preserved fossil of Lithornis promiscuus, an ancient paleognath that lived about 59–56 million years ago. By digitally analyzing its sternum (breastbone) and comparing it with modern birds, the team discovered that Lithornis likely had strong flight muscles and could fly long distances — much like today’s herons or egrets, which regularly travel across continents.
This finding suggests the ancestors of ostriches, emus, and rheas weren’t always land-bound. Instead, they probably flew across oceans to colonize new regions, where their descendants later evolved flightlessness independently.
“This looks like a striking example of convergent evolution,” said Peter Hosner of the Natural History Museum of Denmark, who was not involved in the study.
Today, about 60 paleognath species survive. These include tinamous (still capable of short flights), kiwis, cassowaries, ostriches, emus, and rheas. The shift to flightlessness happened under particular conditions: ground-based food sources and the absence of predators.
Right after the Cretaceous–Paleogene extinction 66 million years ago, predators were scarce, giving many birds the chance to abandon the costly effort of flight. Later, when predators did return, these flightless lineages survived by evolving other defenses — such as sheer size and aggression (cassowaries) or incredible speed (ostriches).
In other words, ostriches, emus, and their relatives didn’t inherit flightlessness from a single ancestor. Instead, each lineage lost flight on its own after spreading across the globe — rewriting the story of how some of the world’s most iconic birds came to be.