Rare Fossil Reveals How Birds Lost Flight

The Ostrich’s Secret: How Flightless Birds Conquered the World

By lisa Park, Chief Editor

For centuries, the world has marveled at the ostrich, the emu, the rhea, the cassowary – grand, flightless birds scattered across continents separated by vast oceans. How did these creatures, seemingly bound to the earth, manage to colonize such disparate lands? The answer, it turns out, lies in a surprising twist of evolutionary history: their ancestors could fly.

The prevailing theory, suggesting that these birds, known as Palenognaths, originated on the supercontinent Pangaea and were simply separated as the landmass broke apart, has been challenged by genetic evidence. While Pangaea began fracturing around 195 million years ago, the last common ancestor of Palenognaths only emerged about 79.6 million years ago, with major lineages diverging between 70 and 62 million years ago. This timeline necessitates a different explanation.

Enter Lithornis promiscus,a 59-56 million-year-old fossil,the most complete Palenognath fossil discovered to date. Klara Widrig, a zoologist at the Smithsonian National museum of Natural History, has been meticulously studying this fossil to unlock the secrets of these birds’ past.

“We haven’t been able to confirm whether Lithornis is a direct ancestor of modern Palenognaths,” Widrig explains, “but its anatomy is the closest we’ve seen to what their ancestors might have looked like.”

Previous research had already established that a relative of lithornis, Calciavis grandis, possessed limited flight capabilities. In a groundbreaking study published in Biology Letters, Widrig and her team analyzed the Lithornis sternum (breastbone) using 3D scanning technology, comparing it to that of modern birds.The results were amazing: the Lithornis sternum closely resembled that of birds capable of long-distance flight, such as large herons and cranes.

“The fact that large herons are capable of crossing continents is remarkable,” says Peter Hosner,a bird curator at the Natural History Museum of Denmark. “Birds with such abilities are actually quite rare.”

This discovery suggests that the ancestors of today’s flightless giants were, in fact, capable of flying across oceans. Upon reaching new lands, they independently evolved into the large, flightless forms we know today – a process known as convergent evolution.

But what drove these birds to abandon flight? Widrig points to two key factors: