Fwd: Low Oxygen Could Have Benefited Dinosaurs
- Repeat post from P&C Nov 7, 2003
--- In Paleontology_and_Climate@yahoogroups.com, npat1@j... wrote:
WASHINGTON (Reuters) - Low oxygen levels could have triggered two
extinctions hundreds of millions of years ago, allowing the dinosaurs
reign supreme over the ancestors of mammals, U.S. researchers said on
Dinosaurs first appeared during a long period of low oxygen and
developed highly efficient breathing mechanisms that allowed them to
thrive while many other species became extinct.
The researchers arrived at the theory by tying in what is known about
physiology of dinosaurs with recent geological evidence suggesting
from 275 million to 175 million years ago, oxygen levels stayed very
-- comparable to levels found now at altitudes of 14,000 feet.
Peter Ward, a University of Washington paleontologist, said he
low oxygen and hot greenhouse conditions caused by intense volcanic
activity may have caused widespread extinctions 250 million years
the boundary between the Permian and Triassic periods, and about 200
million years ago, at the boundary between the Triassic and Jurassic
The Permian-Triassic extinction is believed to have eradicated 90
of all species on Earth, including most protomammals, the immediate
ancestors of true mammals.
The Triassic-Jurassic extinction killed more than half the species,
including many mammals and mammal-like reptiles. But dinosaurs
Ward said he put together three pieces of the puzzle -- the extremely
breathing systems of birds, the finding that many dinosaurs had
physiology, and a report that came out earlier this year showing that
oxygen levels were low during the two extinctions.
"Someone told me they had heard of or seen geese flying above (Mount)
Everest -- at 31,000 feet," said Ward, who presents his findings next
week to a meeting of the Geological Society of America.
The air is thin up there. "If you put a human at 30,000 feet they'd
very, very, quite dead. And the birds are not only up there, they are
doing major heavy exercise," Ward said
Birds and dinosaurs both have holes in their bones. And many of the
largest dinosaurs, such as brontosaurus or apatosaurus, seem to have
lungs attached to a series of thin-walled air sacs that may have acted
something like bellows to move air through the body.
"The reason the birds developed these systems is that they arose from
halfway through the Jurassic Period. They are how the dinosaurs
"The literature always said that the reason birds had sacs was so they
could breathe when they fly. But I don't know of any brontosaurus that
could fly," he added.
"However, when we considered that birds fly at altitudes where oxygen
significantly lower, we finally put it all together with the fact that
the oxygen level at the surface was only 10 percent to 11 percent at
time the dinosaurs evolved."
Currently at sea level, atmospheric oxygen levels are 21 percent. If
giant dinosaurs had to breathe in a low-atmosphere environment, then
an efficient breathing system would have given them a survival
"You'd be really favored for survival in very bad, nasty, low-oxygen
world," Ward said.
Dinosaurs dominated the world for hundreds of millions of years,
65 million years ago. Most scientists agree the impact of an asteroid
meteor was the catalyst.
Low Oxygen Could Have Benefited Dinosaurs
By Maggie Fox, Health and Science Correspondent
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