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"Oxygen Helped Mammals Grow, Study Finds"
From Yahoo (around 2:00 PM EDT):
The text follows:
WASHINGTON - Mammals, once tiny creatures scampering on the forest floor,
grew larger as the amount of oxygen in the air increased over millions of
years, a new study says.
Today mammals, ranging from dogs and cats to elephants, dolphins and people,
dominate the planet.
It's a success story Paul G. Falkowski of Rutgers University and colleagues
say was helped by the more than doubling of oxygen in the air over the last
205 million years. Their findings are published in Friday's issue of the
The researchers measured samples of material deposited on the seafloor going
back millions of years. By measuring the amount of carbon-13 in the samples
they were able to estimate the amount of oxygen in the atmosphere at a
They found that the air contained only about 10 percent oxygen at the time
of the dinosaurs.
By 50 million years ago the oxygen level had risen to 17 percent and it was
23 percent 40 million years ago, they reported. Currently the air contains
about 21 percent oxygen.
The rise of oxygen "almost certainly contributed to evolution of large
animals," the researchers reported. The oxygen needs of mammals and birds
are three to six times as high as reptiles.
The impact of an asteroid or meteorite about 65 million years ago is thought
to have contributed to the demise of the dinosaurs. Their elimination also
created an opportunity for the rise of mammals.
There was an increase in small and medium-sized mammals in the first few
million years after the end of the dinosaurs, the researchers reported. A
second surge, from medium to large sizes, was seen between 50 million and 40
million years ago, they reported.
The research was funded by the National Science Foundation.
This goes against earlier (somewhat flawed) studies that showed the O2
levels were very much higher during the Mid to Late Jurassic. I have
suggested that the increased O2 levels enabled (or "eased") the dinos to
growing larger, since you can generate more energy with more O2, easier.
I'd need to see the details of how amount of C13 in OCEAN deposits
correlates to O2 levels in the atmosphere.