T. rex's bones contained large airspaces connected to air sacs within its body cavity. In fact, more than 10% of T. rex's body volume may have been made up of "inflatable" air space. In scientific jargon, this is called pneumaticity. Biologists have long known that theropods (...) had pneumatic bones.
(...) Matt got interested in pneumaticity as an undergrad in Oklahoma, where he spent his Saturdays running dinosaur bones through the CT scanner at his local hospital. There, he discovered that one of Sauroposeidon's four and a half foot vertebrae would have been surprisingly light and could reach 90% air by volume! Digging deeper into how the airspaces in these massive animals evolved pointed Matt towards a seemingly unlikely model organism: the chicken.
You may know that birds have hollow bones (...) — but you may not have considered how those airspaces work. First off, a bird's respiratory system is a bit different from ours: their lungs are ventilated by a set of forward air sacs and another set of rear air sacs. With this arrangement, birds can get oxygen out of air while both inhaling and exhaling — an efficient system, which allows birds to perform feats that mammals could never hope to accomplish, like flying over the Himalayas. As a baby bird grows, its air sacs develop a system of outgrowths and tubes that invade and pneumatize the bird's bones, forming hollows. The forward air sacs are connected to the hollow bones at the front of the bird's body, and the rear air sacs are connected to the hollow bones at the back of the bird's body. This system of pneumatized bones provides the bird with a skeleton that is both light and strong.
Matt wondered if the same sort of dual air sac system might be responsible for the airspaces in birds' dinosaur ancestors. But of course, air sacs are built from thin, soft tissue — and so, are not preserved in any known dinosaur fossils. How could fossilized pneumatic bones alone reveal which air sacs dinosaurs had?
After studying up on chicken development, Matt came up with a way to test the hypothesis that dinosaurs had a fore/rear air sac system. Birds' pneumatic bones always develop in the same way: soon after the bird hatches, the forward air sacs begin to invade the vertebrae in the neck, and later, the rear air sacs begin to invade the vertebrae towards the pelvis. Then the airspaces spread through the vertebrae until the hollows meet in the middle and the whole vertebral column is pneumatized...
Well, at least usually that's how it works — but Matt knew that occasionally, due to a small developmental glitch, the airspaces in the necks and the pelvises of some birds never quite meet up, leaving them with a few non-pneumatized vertebrae in the middle of their spine. Matt reasoned that if the same dual air sac system were present in dinosaurs, then some dinosaur skeletons should have the same "gap" in the pneumatization of their spines. But he had little hope of actually finding that key piece of evidence: "I didn't really expect to find such things in dinosaurs — not because they're not there, but because they don't seem to be common and our sample size is so small."
Matt decided to focus on other research instead of chasing an elusive piece of evidence — evidence that turned out to be not so elusive after all. While rereading some classic scientific papers from the early 1900s on sauropod dinosaurs, he noticed that the authors described pneumatized vertebrae in the fore and rear of the animals but solid vertebrae in the middle! The key evidence had been available for a century — but no one had even noticed the pattern until Matt came along with a hypothesis to explain it. And emailing a colleague about his "re"-discovery turned up yet another case of the telltale gap in a tyrannosaur.
For Matt, these examples sealed the deal: dinosaurs did have a fore/rear air sac system. As he puts it, "There was already plenty of evidence that saurischians [the dinosaur clade containing theropods and sauropods] had air sacs like birds — but this, to me, is the last stake in the coffin...There's just no other way you could get this pattern."
D'autres informations sur la respiration des oiseaux trouvées ici:
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