Reviewing the birth of feathered flight
My daughter has only known a world where birds are considered dinosaurs. My first impressions of dinosaurs barely even hinted at that idea, and it’s been interesting for the two of us to feel our way through some of the assumptions this lineage brings up from our two perspectives. One thing that has come up (not just with dinosaurs, but with all evolution) is how there’s rarely a bright line separating one animal from their descendants. For instance, what traits make a bird something unique from other animals?
With so many other animals using supposed trademarks of birds, like dry eggs, body fluff, and air sacs in the respiratory system, it’s hard to pick something firm to specify ‘birdiness.’ But feathered flight seems like a nice place to look, since while other animals could fly, and may have had fluff, it looks like you could say that only birds used as the foundation for their flight. Even birds that no longer fly have ancestry that carry traits of flight-friendly plumage.
What counts as flight-friendly feathers? A paper out of Yale honed in on asymmetric feathers, similar to the primaries on modern bird wings. This shape helps create lift, so it seems like as clear a deliminator as we’re going to get.
A survey of feather impressions ended up putting species like Confuciusornis and Eopengornis at the head of the pack. They also happen to have other structural traits that further support their ability to fly. Long-time celebrity species like Archaeopteryx and Microraptor came close, but their feathers just didn’t come close enough on their trailing edges to be capable of modern bird flight.
This is not to say that the famous “first bird” was grounded. They very likely at least glided, and were possibly capable of some sort of powered flight. But with this new comparison in feather structure, that form of flight wouldn’t have matched modern flight. If we can model what flight they were doing, it may help us figure out how and why it isn’t (apparently) around today.
Source: When Did Dinosaurs Learn to Fly? by Brian Switek, Laelaps