But they aren’t the ancestors of the modern ones. They died out, but why? From ScienceDaily:
“We know that birds in the early Cretaceous, about 115 to 130 million years ago, were capable of flight but probably not as well adapted for it as modern birds,” said Atterholt, who is now an assistant professor and human anatomy instructor at the Western University of Health Sciences in Pomona, California. “What this new fossil shows is that enantiornithines, though totally separate from modern birds, evolved some of the same adaptations for highly refined, advanced flight styles.”
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If enantiornithines in the late Cretaceous were just as advanced as modern birds, however, why did they die out with the dinosaurs while the ancestors of modern birds did not?
“This particular bird is about 75 million years old, about 10 million years before the die-off,” Atterholt said. “One of the really interesting and mysterious things about enantiornithines is that we find them throughout the Cretaceous, for roughly 100 million years of existence, and they were very successful. We find their fossils on every continent, all over the world, and their fossils are very, very common, in a lot of areas more common than the group that led to modern birds. And yet modern birds survived the extinction while enantiornithines go extinct.”
One recently proposed hypothesis argues that the enantiornithines were primarily forest dwellers, so that when forests went up in smoke after the asteroid strike that signaled the end of the Cretaceous — and the end of non-avian dinosaurs — the enantiornithines disappeared as well. Many enantiornithines have strong recurved claws ideal for perching and perhaps climbing, she said.
“I think it is a really interesting hypothesis and the best explanation I have heard so far,” Atterholt said. “But we need to do really rigorous studies of enantiornithines’ ecology, because right now that part of the puzzle is a little hand-wavey.”
We know we are getting somewhere with the science part of it all when “hand-wavey” is seen as a problem.
“What is most exciting, however, are large patches on the forearm bones. These rough patches are quill knobs, and in modern birds they anchor the wing feathers to the skeleton to help strengthen them for active flight. This is the first discovery of quill knobs in any enantiornithine bird, which tells us that it was a very strong flier.” Paper. (open access) – Jessie Atterholt, J. Howard Hutchison, Jingmai K. O’Connor. The most complete enantiornithine from North America and a phylogenetic analysis of the Avisauridae. PeerJ, 2018; 6: e5910 DOI: 10.7717/peerj.5910
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See also: Mystery: ENST comments on the fossil African turaco found in North America at 52 mya …
Shaking the bird family tree: African-type bird fossil from 52 mya found in North America. In this case, what the fossil record tells us poses a problem for biogeography (the distribution of life forms worldwide over time). At 52 million years ago, North America was thousands of kilometres from Africa. Did the birds migrate? Could they?
Reptile had bird-like head 100 million years before birds