New genetic data reshapes the story of flightless birds
Birds are often celebrated for their ability to conquer the skies, but a growing body of research suggests the opposite may be true for the ancestors of today’s flightless giants. A new study points to a surprisingly recent shift from flying ancestry to ground-dwelling endurance, proposing that ancestors of ostriches, emus, kiwis, and their relatives once crossed oceans and later became land-bound giants. This challenges long-standing ideas about how these birds reached distant continents such as Africa, Australia, and South America, and it reframes the timing of one of evolution’s most dramatic transformations.
A fossil clue that hints at flying ancestors
Scientists examined a remarkably well-preserved fossil breastbone from an early flightless-bird ancestor, a key piece in understanding how these birds moved and dispersed. The evidence suggests that these ancient birds possessed flight apparatus capable of sustained flight, similar in some respects to modern pigeons and parrots. The researchers argue that such flying capabilities would have enabled long-distance oceanic travel, allowing these birds to colonize new lands long before they became the terrestrial giants we associate with ostriches and their kin today.
The findings, published in Biology Letters, imply a more dynamic picture of bird biogeography. Rather than departing from a single landmass when Gondwana began to break apart, these birds could have moved across oceans, establishing populations on distant shores while their descendants gradually shifted toward larger sizes and flightlessness once they faced different ecological pressures on land.
How ocean journeys likely unfolded
Ocean crossing by flight-capable ancestors would have required endurance, navigational ability, and access to reliable food sources during travel. The fossil evidence supports the possibility that early flight-capable birds could traverse hundreds or thousands of kilometers before taking root on new continents. Once on a new landmass, geographic isolation and local ecological opportunities would facilitate diversification, with some lineages remaining flight-capable for longer than others or losing flight altogether over evolutionary timescales.
Why flight was abandoned in some lineages
Two central drivers are proposed for the loss of flight. First, a dependable food supply on the ground reduces the pressure to retain flight for foraging. Second, a relaxing of predation pressure—particularly after the extinction of large dinosaurs—lessened the survival advantage of staying airborne. Under these conditions, natural selection favored strong legs for running, powerful kicks for defense, and other ground-adapted traits, gradually eroding the features needed for flight. Over millions of years, these flight-capable ancestors evolved into the diverse, robust flightless birds we recognize today, from towering ostriches to flightless rails and kiwis.
What remains mysterious for scientists
Even as this study clarifies the mechanism of global dispersal, it raises fresh questions about survival and diversification. How did flightless clades persist across continents with such reduced dispersal abilities? Why do some lineages stay flightless while others retain flight or re-evolve it under certain ecological circumstances? The research places Paleognathae—an ancient group that includes ostriches, emus, cassowaries, and the extinct moas and elephant birds—at the center of a larger puzzle about evolution, dispersal, and the balance between mobility and local adaptation.
Broader implications for evolution and biogeography
By illuminating a scenario in which flightlessness arises after successful oceanic dispersal, scientists gain a more nuanced view of how ancient birds navigated shifting ecosystems. This perspective helps explain how flight, once a defining trait, could be exchanged for land-based advantages like speed, power, and resilience on varied terrains. The study’s insights contribute to the broader field of biogeography—how species spread across the globe—and highlight the intricate and often surprising paths evolution can take in response to changing climates, predators, and food webs.
