zeke
Member
I know that bird respiratory systems "stands in stark contrast to that of other animals". I know that theropod dinosaurs did not have avian lungs. I know that avian respiration is a tricky question and not likely to be preserved in the fossil record. I know that we do not have enough evidence to say ‘x’ is really derived from ‘y'. I know that birds have always been birds just as dogs have always been dogs.
Are birds dinosaurs? New evidence muddies the picture
A bird’s respiratory system stands in stark contrast to that of other animals, Quick says. Flying requires a lot of energy and oxygen. As a result, over time, birds have developed a highly efficient lung and respiratory system that allows them to take in enough oxygen and exchange carbon dioxide efficiently enough to allow them to fly. “The way they move air across their lungs is really different from the way we do it,†she says. “It’s very special. We use a diaphragm to change the volume of our lungs. They don’t change the volume at all, because they have these really specialized collapsible structures, really thin-walled, compliant air sacs.†Birds also have a special skeleton, Quick says, that keeps the air sac from collapsing when the bird inhales.
In the study, Quick and Ruben detailed new findings about this specialized skeleton, including an immobile thigh bone that is locked into the body wall and provides extra skeletal support for the birds’ flabby air sac. But the more controversial news was the underlying implication: that if dinosaurs are the ancestors of birds, it seems unlikely that scientists would have found no trace of this highly specialized system in any dinosaur fossils.
“We’re suggesting that theropod dinosaurs did not have a bird-like lung,†Quick says. That, in turn, suggests that theropods may not be the ancestors of birds, she says, but instead may represent an extinct lineage. “I don’t think it’s clear what theropods are at all, as far as what they gave rise to or what gave rise to them.†One possibility, she says, is that theropods and birds might both be derived from a common ancestor.
The evolution of avian respiration is a tricky question, Varricchio says, because it’s a complex system that’s not likely to be preserved in the fossil record. “We’re really trying to predict what the lungs [of dinosaurs] look like, and they don’t leave any trace on any bone.†Even in birds, it’s not necessarily straightforward, he adds: For example, birds brooding on a clutch of eggs can’t use their sternums as a bellows — they have to use their abdominal muscles, suggesting that although the sternum is important, it may not be absolutely necessary for birds to breathe. Still, in their paper, Quick and Ruben do make a good point that the abdominal structure of most theropod dinosaurs is distinct from that of birds, Varricchio says. So, he adds, that structure is “probably not doing the exact same thing†when it comes to breathing.
Quick insists that she didn’t set out to disprove a bird-dinosaur link. “I just don’t think we have enough information to make a definitive conclusion,†she adds. “[It’s] the nature of the fossil record — it’s so spotty. While we can have some good preservation, we don’t have the whole picture to say that ‘x’ is really derived from ‘.’â€
Full article here
A bird’s respiratory system stands in stark contrast to that of other animals, Quick says. Flying requires a lot of energy and oxygen. As a result, over time, birds have developed a highly efficient lung and respiratory system that allows them to take in enough oxygen and exchange carbon dioxide efficiently enough to allow them to fly. “The way they move air across their lungs is really different from the way we do it,†she says. “It’s very special. We use a diaphragm to change the volume of our lungs. They don’t change the volume at all, because they have these really specialized collapsible structures, really thin-walled, compliant air sacs.†Birds also have a special skeleton, Quick says, that keeps the air sac from collapsing when the bird inhales.
In the study, Quick and Ruben detailed new findings about this specialized skeleton, including an immobile thigh bone that is locked into the body wall and provides extra skeletal support for the birds’ flabby air sac. But the more controversial news was the underlying implication: that if dinosaurs are the ancestors of birds, it seems unlikely that scientists would have found no trace of this highly specialized system in any dinosaur fossils.
“We’re suggesting that theropod dinosaurs did not have a bird-like lung,†Quick says. That, in turn, suggests that theropods may not be the ancestors of birds, she says, but instead may represent an extinct lineage. “I don’t think it’s clear what theropods are at all, as far as what they gave rise to or what gave rise to them.†One possibility, she says, is that theropods and birds might both be derived from a common ancestor.
The evolution of avian respiration is a tricky question, Varricchio says, because it’s a complex system that’s not likely to be preserved in the fossil record. “We’re really trying to predict what the lungs [of dinosaurs] look like, and they don’t leave any trace on any bone.†Even in birds, it’s not necessarily straightforward, he adds: For example, birds brooding on a clutch of eggs can’t use their sternums as a bellows — they have to use their abdominal muscles, suggesting that although the sternum is important, it may not be absolutely necessary for birds to breathe. Still, in their paper, Quick and Ruben do make a good point that the abdominal structure of most theropod dinosaurs is distinct from that of birds, Varricchio says. So, he adds, that structure is “probably not doing the exact same thing†when it comes to breathing.
Quick insists that she didn’t set out to disprove a bird-dinosaur link. “I just don’t think we have enough information to make a definitive conclusion,†she adds. “[It’s] the nature of the fossil record — it’s so spotty. While we can have some good preservation, we don’t have the whole picture to say that ‘x’ is really derived from ‘.’â€
Full article here
. 