Caihong juji, a 160 million-year-old bird-like dinosaur found in Hebei Province in China, which had an iridescent, rainbow crest.Credit...Velizar Simeonovski/University of Texas, Austin
Carl Zimmer has an interesting post on his Origins blog over at the New York Times. Scientists have long wondered how and when birds first take flight. It's long been established that birds are dinosaurs. Early birds evolved into two divergent groups. Modern birds belong to ornithuromorphs, while the other group, the enantiornithines, actually dominated the skies for millions of years. A new paper in the journal Cretaceous Research by lead author Dr. Jingmai O’Connor, a paleontologist at the Field Museum in Chicago, found that enantiornithine birds hatched with bare bodies, but with fully feathered wings. As adults, they molted and then replaced all their feathers at the same time. Before the new feather growth was complete, they had to survive without the usual insulation.
This lineage of birds survived until 66 million years ago, when an asteroid struck the Earth. Roughly three-quarters of all species on the planet were wiped out, including all feathered dinosaurs except the ornithuromorphs.
Dr. O’Connor and other paleontologists are investigating why those birds survived when all other feathered reptiles vanished. The debris from the impact caused widespread wildfires, followed by darkness and a plunge in temperatures. Terrestrial ecosystems collapsed. Feathered dinosaurs that ate leaves or small animals might have starved. But birds had evolved beaks that allowed them to eat the vast quantities of seeds buried in the ground.
Dr. O’Connor thinks other factors may have also been at play. After thriving for 70 million years or more, enantiornithines may have suddenly become vulnerable in the cold weather after the asteroid when they molted all their feathers at once.
“You throw them in an impact winter, where now global temperatures have decreased and there’s resource scarcity, it’s just going to push them over the edge,” Dr. O’Connor said.