Although their non-avian equivalents have long since died out, the dinosaurs are alive and well in the form of birds. These modern-day feathered flying animals still belong to the same evolutionary group – the Coelurosauria – that once included the Dromaeosauridae, the family that includes the famous Velociraptor.
A new study published in the journal PLOS ONE reveals that contemporary baby birds may be showing us how their distant, Cretaceous-age ancestors developed the ability to fly in the first place. Using high-resolution X-ray imagery of our young feathered friends trying to take flight, researchers have discovered that they coordinate their legs and wings to give themselves little boosts, just like adult birds.
The team suspects that this mechanism is how ancient feathered dinosaurs first learned to shake off the chains of gravity and take to the skies – if only very briefly. Despite the fact that they possessed underdeveloped flight muscles and skeletal systems, just like their juvenile descendants, they were probably able to generate significant amounts of lift.
“Baby birds anatomically look a lot like some of the dinosaur fossils that we see,” lead author Ashley Heers, a postdoctoral researcher in the American Museum of Natural History's Division of Paleontology, said in a statement. “And so, by studying baby birds and looking at how they actually use these dinosaur-like anatomies, we can get a better sense of how these long-extinct animals might have been using their wings.”
The Munich Archaeopteryx specimen, a bird-like dinosaur that clearly had feathers, was perhaps capable of very small amounts of lift. Luidger/Wikimedia Commons; CC BY-SA 3.0
Birds as we know them today first appeared about 100 million years ago, during the last chapter in the story of the non-avian dinosaurs. Their immediate ancestors were not yet equipped for true flight: Instead of large wings, they had smaller feathered arms, or “protowings,” along with poorly developed, non-rigid forelimb skeletal networks.
However, modern baby birds with similar anatomies have been seen to flap their wings as they run up slopes, sometimes giving them the ability to briefly fly – a behavior known as wing-assisted incline running (WAIR). The team of researchers wondered how their skeleton was behaving as they did this, so they viewed them through X-rays as they scarpered around.
As they ran around and engaged in a bit of WAIR, the researchers could see that their wing strokes were very similar to those of adult birds. This means that, despite their underdeveloped skeleton, they can still produce all the elements of adult, advanced flight.
A baby bird flaps its wings to give itself a little boost as it runs up a slope. American Museum of Natural History via YouTube
Taking everything into consideration, the researchers make the not-unreasonable assumption that the birds’ ancient predecessors, with their similarly underdeveloped adult anatomies, could manage basic flight in the same way. If true, researchers may have stumbled across the original mechanism that allowed full flight to eventually evolve in birds.
“The transition from ground-living dinosaurs to flight-capable birds is one of the major evolutionary transitions in vertebrate history, because flight is the most physically demanding form of locomotion,” Heers noted.
The ability to fly isn’t the only characteristic that makes something a bird: bats, insects, pterosaurs, and even a species of snail can all do this, and they aren’t classified within the group Aves. However, this does suggest that the evolution of flight has evolved on only a select few occasions, so understanding how it comes about in distally related groups – a process known as “convergent evolution” – is an important task for researchers.