Most do not realize that in the last age of the dinosaurs the late Cretaceous period, more than 65 million years ago there were many species of birds, avian dinosaurs, and related small feathered dinosaurs. After the demise of the dinosaurs because of one or more meteor impacts only one lineage of birds survived.
From: https://phys.org/news/2018-11-rare-fossil-bird-deepens-mystery.html
During the late Cretaceous period, more than 65 million years ago, birds belonging to hundreds of different species flitted around the dinosaurs and through the forests as abundantly as they flit about our woods and fields today.
But after the cataclysm that wiped out most of the dinosaurs, only one group of birds remained: the ancestors of the birds we see today. Why did only one family survive the mass extinction?
A newly described fossil from one of those extinct bird groups, cousins of today's birds, deepens that mystery.
The 75-million-year-old fossil, from a bird about the size of a turkey vulture, is the most complete skeleton discovered in North America of what are called enantiornithines (pronounced en-an-tea-or'-neth-eens), or opposite birds. Discovered in the Grand Staircase-Escalante area of Utah in 1992 by University of California, Berkeley, paleontologist Howard Hutchison, the fossil lay relatively untouched in University of California Museum of Paleontology at Berkeley until doctoral student Jessie Atterholt learned about it in 2009 and asked to study it.
Atterholt and Hutchison collaborated with Jingmai O'Conner, the leading expert on enantiornithines, to perform a detailed analysis of the fossil. Based on their study, enantiornithines in the late Cretaceous were the aerodynamic equals of the ancestors of today's birds, able to fly strongly and agilely.
"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."
The fossil's breast bone or sternum, where flight muscles attach, is more deeply keeled than other enantiornithines, implying a larger muscle and stronger flight more similar to modern birds. The wishbone is more V-shaped, like the wishbone of modern birds and unlike the U-shaped wishbone of earlier avians and their dinosaur ancestors. The wishbone or furcula is flexible and stores energy released during the wing stroke.
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.
Read more at: https://phys.org/news/2018-11-rare-fossil-bird-deepens-mystery.html#jCp
From: https://phys.org/news/2018-11-rare-fossil-bird-deepens-mystery.html
During the late Cretaceous period, more than 65 million years ago, birds belonging to hundreds of different species flitted around the dinosaurs and through the forests as abundantly as they flit about our woods and fields today.
But after the cataclysm that wiped out most of the dinosaurs, only one group of birds remained: the ancestors of the birds we see today. Why did only one family survive the mass extinction?
A newly described fossil from one of those extinct bird groups, cousins of today's birds, deepens that mystery.
The 75-million-year-old fossil, from a bird about the size of a turkey vulture, is the most complete skeleton discovered in North America of what are called enantiornithines (pronounced en-an-tea-or'-neth-eens), or opposite birds. Discovered in the Grand Staircase-Escalante area of Utah in 1992 by University of California, Berkeley, paleontologist Howard Hutchison, the fossil lay relatively untouched in University of California Museum of Paleontology at Berkeley until doctoral student Jessie Atterholt learned about it in 2009 and asked to study it.
Atterholt and Hutchison collaborated with Jingmai O'Conner, the leading expert on enantiornithines, to perform a detailed analysis of the fossil. Based on their study, enantiornithines in the late Cretaceous were the aerodynamic equals of the ancestors of today's birds, able to fly strongly and agilely.
"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."
The fossil's breast bone or sternum, where flight muscles attach, is more deeply keeled than other enantiornithines, implying a larger muscle and stronger flight more similar to modern birds. The wishbone is more V-shaped, like the wishbone of modern birds and unlike the U-shaped wishbone of earlier avians and their dinosaur ancestors. The wishbone or furcula is flexible and stores energy released during the wing stroke.
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.
Read more at: https://phys.org/news/2018-11-rare-fossil-bird-deepens-mystery.html#jCp