From Scientific Blogging:
Theropod Dinosaurs Evolved Into Birds? Not Likely, Says Study
By News Staff | June 9th 2009 01:00 AM
Paleontologists and some in biology have long believed that modern birds are the direct descendants of ancient, meat-eating dinosaurs.
Researchers at Oregon State University contend they have made a fundamental new discovery about how birds breathe and have a lung capacity that allows for flight – and the finding means it’s unlikely that birds descended from any known theropod dinosaurs.
It’s been known for decades that the femur, or thigh bone in birds is largely fixed and makes birds into “knee runners,” unlike virtually all other land animals, the OSU experts say. What was just discovered, however, is that it’s this fixed position of bird bones and musculature that keeps their air-sac lung from collapsing when the bird inhales.
Warm-blooded birds need about 20 times more oxygen than cold-blooded reptiles, and have evolved a unique lung structure that allows for a high rate of gas exchange and high activity level. Their unusual thigh complex is what helps support the lung and prevent its collapse. …
These studies were just published in The Journal of Morphology, and were funded by the National Science Foundation. …
The implication, the researchers said, is that birds almost certainly did not descend from theropod dinosaurs, such as tyrannosaurus or allosaurus. The findings add to a growing body of evidence in the past two decades that challenge some of the most widely-held beliefs about animal evolution.
“For one thing, birds are found earlier in the fossil record than the dinosaurs they are supposed to have descended from,” Ruben said. “That’s a pretty serious problem, and there are other inconsistencies with the bird-from-dinosaur theories.
“But one of the primary reasons many scientists kept pointing to birds as having descended from dinosaurs was similarities in their lungs,” Ruben said. “However, theropod dinosaurs had a moving femur and therefore could not have had a lung that worked like that in birds. Their abdominal air sac, if they had one, would have collapsed. That undercuts a critical piece of supporting evidence for the dinosaur-bird link. …
The newest findings, the researchers said, are more consistent with birds having evolved separately from dinosaurs and developing their own unique characteristics, including feathers, wings and a unique lung and locomotion system.
There are some similarities between birds and dinosaurs, and it is possible, they said, that birds and dinosaurs may have shared a common ancestor, such as the small, reptilian “thecodonts,” which may then have evolved on separate evolutionary paths into birds, crocodiles and dinosaurs. The lung structure and physiology of crocodiles, in fact, is much more similar to dinosaurs than it is to birds.
“We aren’t suggesting that dinosaurs and birds may not have had a common ancestor somewhere in the distant past,” Quick said. “That’s quite possible and is routinely found in evolution. It just seems pretty clear now that birds were evolving all along on their own and did not descend directly from the theropod dinosaurs, which lived many millions of years later.”
See also here.
The Problem With Selfish Gene Theory, By Gerhard Adam: here.
Fossil Solves Mystery of Dinosaur Finger Evolution: here.
Largest carnivorous dinosaur tooth in Spain described: here.