A new twist on how flightless birds spread across continents
For generations, scientists have wondered how flightless giants like ostriches, emus, and kiwis ended up on continents as distant as Africa, Australia, and South America. The traditional view tied this broad dispersal to the ancient supercontinent Gondwana, arguing that its breakup around 150 million years ago carried lineages apart and set the stage for flightlessness. A fresh mix of genetic data and fossil evidence now points to a different story: these birds may have mastered long-distance flight in their ancestors and crossed oceans before adapting to land life on new shores.
Fossil clues rewrite the timeline
A team of researchers examined a comparatively well-preserved fossil sternum, or breastbone, of an early flightless bird ancestor. The sternum is a key anchor for flight muscles, and the team found features indicating that this ancestor could fly long distances — similar to modern pigeons and parrots. The idea is that these ancestors reached new continents while still capable of flight; once there, lineages gradually grew larger and lost the ability to take to the skies. In short, oceanic dispersal happened first, followed by terrestrial life and the eventual loss of flight in many descendants.
Why flight was eventually abandoned
Scientists propose two main drivers for the shift from flight to flightlessness. First, when food on the ground was plentiful and predators were scarce, there was little evolutionary pressure to stay airborne. The extinction of large predators, including dinosaurs, created ecological space for ground-dwelling birds to thrive. Over countless generations, traits suited to running, powerful kicking defenses, and robust legs were selected, making flight unnecessary or even disadvantageous. Over time, wings shortened and bodies grew heavier, cementing a flightless lifestyle in many lineages.
The ongoing mystery and the broader picture
Even as the fossil record and genetics illuminate a path for oceanic dispersal before terrestrial life, researchers acknowledge remaining puzzles. Co-author and zoologist Helen James notes the paradox of today’s doughy, flight-limited birds: Paleognathae — which includes ostriches, emus, cassowaries, kiwis, and extinct giants like moas and elephant birds — show a complex mix of dispersal histories and survival strategies. The new findings imply that ancient birds could traverse vast distances by air, only to settle, diversify, and lose flight when ecological conditions favored land-based existence. This challenges a simplistic view that continental drift alone dictated where these birds ended up and how they evolved.
What this means for evolution and future research
The study highlights how evolution can flip a once-ornament of the skies into a landbound powerhouse, driven by ecological opportunities and constraints. By integrating fossils with modern genomics, scientists can reconstruct past biogeography with greater nuance, revealing how ancient flying ancestors possibly seeded remote regions before shifting toward terrestrial life. The tale of flight and flightlessness in these birds offers a vivid example of evolution’s versatility in the face of shifting ecosystems and climates.
Key terms in context
Paleognathae: the wildlife group that includes ostriches, emus, kiwis, cassowaries, and some extinct giants; Gondwana: the southern supercontinent whose breakup has long framed bird dispersal theories; sternum: the breastbone, a critical site for flight muscle attachment used to infer flight capability in fossils.
Looking ahead
Researchers advocate for more fossil discoveries and intensified comparative genomics across paleognath lines. Pinpointing the timing and routes of ancient ocean crossings will deepen our understanding of how flightless birds emerged, adapted, and endured through sweeping ecological shifts over millions of years.
