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CNN on Lungs and Feathers (LONG)



Thought this may be of interest to the list:

Lung Fossils Suggest Dinos Breathed in Cold Blood


Science
25-DEC-97
By Ann Gibbons

When John Ruben first laid eyes on a high-quality photo of the so-called
"feathered" dinosaur from China last year, he was stunned. It wasn't the
featherlike structures that riveted his attention--he dismissed them as
collagen fibers (see sidebar)--but the theropod dinosaur's innards,
which were outlined in the slab of stone. "My eyes popped out," recalls
Ruben, a respiratory physiology expert at Oregon State University in
Corvallis. "I realized that here was the first evidence in the soft
tissue that theropods had the same kind of compartmentalization of
lungs, liver, and intestines that you would find in a crocodile"--and
not in a bird.

To prove that notion, Ruben and his graduate students sectioned
crocodiles and other reptiles and found that their lung structures
resembled the images of several flattened fossil dinosaurs from China.
On page 1267, Ruben uses this lung evidence to argue not only that
dinosaurs were incapable of the high rates of gas exchange needed for
warm-bloodedness, but also that their bellowslike lungs could not have
evolved into the high-performance lungs of modern birds. Thus, he
challenges two of the reigning hypotheses concerning dinosaurs: that
they were warm-blooded and that they gave rise to birds.

Coming hot on the heels of another controversial paper that concludes
that digits in bird wings could not have developed from dinosaur
forelimbs (Science, 24 October, p. 666), Ruben's report is part of a
"one-two punch to the dinosaur origins of birds hypothesis," says
paleontologist James Farlow of Indiana University-Purdue University in
Fort Wayne. But while many dinosaur experts say they welcome Ruben's
novel approach, few are willing to embrace his conclusions so far. "This
is exactly the kind of research we need," says Lawrence Witmer, an
evolutionary biologist at Ohio University College of Osteopathic
Medicine in Athens. And it's definitely weakening the case for
warm-blooded dinosaurs. But many researchers, including Farlow and
Witmer, think there's persuasive evidence that birds are descendants of
dinosaurs. Says Farlow: "[This] is like a breath of fresh air, but it's
going to ruffle a lot of feathers."

To test whether dinosaurs were really endotherms--warm-blooded animals
able to generate their own heat--Ruben and graduate students Terry Jones
and Nick Geist have sought to identify the signatures of endothermy,
such as a scroll-like structure in the nose, in the bones of living
animals. They have argued that dinosaurs lack such structures (Science,
30 August 1996, p. 1204). But what they really needed was improbable--a
look at a dinosaur's lungs to see if they were efficient enough to power
a warm-blooded animal.

The improbable happened last year, how ever, when Ruben saw photos of
several specimens of Sinosauropteryx, a small, meat-eating dinosaur from
the 120-million-year-old Yixian formation in northeastem China. The fine
silt from an ancient lake preserved the animals' soft structures,
including a clear "silhouette of the lungs" of one dinosaur, says
paleontologist Larry Martin of the University of Kansas, Lawrence, who
has seen the fossils.

When Ruben looked at the photos, it was "immediately apparent" to him
that the dinosaur's lungs were arranged in a way that closely matched
that of crocodiles. The theropods had two major cavities--the thoracic
cavity containing the lungs, liver, and heart; and the abdominal cavity
containing intestines and other organs. These were completely separated
from each other by the diaphragm, as is the case in crocodiles. Birds
have no such separation.

In living crocodilians, the function of this separation is to provide an
airtight seal between the cavities. Then, when the diaphragmatic muscles
contract, they pull back the liver and create negative pressure in the
thoracic cavity, allowing air to fill the bellows-type lungs. Birds
don't need such a separation between the cavities, because air in their
lungs moves one way through millions of tiny air passages, drawn by the
expansion and contraction of air sacs throughout their bodies.

Birds' flow-through lung system has plenty of surface area and is
especially efficient at exchanging oxygen for carbon dioxide. (Mammals
have yet another system that allows efficient gas exchange.) The
bellowslike reptilian lung, however, provides much less area for gas
exchange, and reptiles cannot absorb oxygen at the high rates needed to
sustain intense activity. Ruben also showed that theropods and
crocodiles share a distinct hip structure, linked to muscles that help
bring air into the bellows-like lungs. All in all, says Ruben, it's
"pretty solid evidence that theropods could not have had a modem,
high-performance avian-style lung ... and were stuck with an unmodified,
bellowslike lung." Says Martin: "Support for the hot-blooded dinosaur
hypothesis now has the rigidity of a marshmallow." The evolutionary
implications are even more far-reaching. Ruben argues that a transition
from a crocodilian to a bird lung would be impossible, because the
transitional animal would have a life-threatening hernia or hole in its
diaphragm. "There may well be a relationship between dinosaurs and
birds, but it's not the linear relationship you see in museum displays,"
he says.

Ruben's analysis is "another nail in the coffin of the warm-blooded
dinosaur theory," says paleontologist Peter Dodson of the University of
Pennsylvania, Philadelphia. But many other researchers say his case is
not airtight. They point out that Ruben relied on photos showing a lung
outline that is little more than "smudges on rock," says Witmer. What's
more, Ruben's inferences are based on a flattened, two-dimensional
fossil. "You would expect some deformation when the organs squish out,"
says Witmer, who suggests, only half-jokingly, that Ruben flatten his
alligators with a steamroller for comparison. And the evolutionary
transition from the actual theropod lung, rather than the modem
crocodilian analog, might be easier.

Indeed, even if Ruben's analysis of lung structure holds up, it would
have to be weighed against "a mountain" of other evidence supporting the
dinosaurian origin of birds, says Farlow. Still, he finds Ruben's
findings of a crocodilian-type lung for theropods "compelling."
Fortunately, the Yixian formation is so rich in fossils that more
specimens of Sinosauropteryx are likely to turn up. And if the same lung
structure appears in enough fossils, Ruben's case will gather
considerable weight.

RELATED ARTICLE: Plucking the Feathered Dinosaur

Exactly 1 year ago, paleontologists were abuzz about photos of a
so-called "feathered dinosaur," which were passed around the halls at
the annual meeting of the Society of Vertebrate Paleontology (Science, 1
November 1996, p. 720). The Sinosauropteryx specimen from the Yixian
Formation in China made the front page of The New York Times, and was
viewed by some as confirming the dinosautian origins of birds. But at
this year's vertebrate paleontology meeting in Chicago late last month,
the verdict was a bit different: The structures are not modern feathers,
say the roughly half-dozen Western paleontologists who have seen the
specimens.

The stiff, bristlelike fibers that outline the fossils lack the detailed
organization seen in modern feathers, says Alan Brush, an ornithologist
at the University of Connecticut, Storrs, who specializes in feather
structure. Brush was part of a "dream team" sent to China this spring by
The Academy of Sciences in Philadelphia to view the fossils.

But just what the structures are--and whether they link birds and
dinosaurs--is still under debate. Noting that the outline of the
dinosaur skin is hard to discern in the fossilized stone, another dream
team member, paleontologist Larry Martin of Kansas University, Lawrence,
thinks the structures are frayed collagenous fibers beneath the
skin--and so have nothing to do with birds. Zoologist John Ruben of
Oregon State University in Corvallis dissected a sea snake's tail to
show that such fibers can indeed look feathery (see photo). Others,
including Brush and Philip Currie, a paleontologist at the Royal Tyrrell
Museum of Palaeontology in Drumbeller, Canada, describe the bristlelike
fibers as "proto-feathers"--fibers that may be hollow and made of the
same kind of keratin as feathers.

Meanwhile, Ji Qiang, director of the Chinese Geology Museum in Beijing,
insists that the fibers are "obvious primitive feathers." But a paper in
press at Nature by another group of Chinese researchers doesn't make
that claim, says Currie. Measuring the width of the fibers under a
scanning electron microscope or testing whether they're made of collagen
or keratin could resolve the debate. Some of these tests are under way,
Currie adds.

Article Dated 24-DEC-97

COPYRIGHT 1997 American Association for the Advancement of Science


Bryan R. Stahl

"This was none of the good Lord's pleasure,
For the Spirit He breathed in Man is free;
But what comes after is measure for measure,
And not a God that afflicteth thee..."  Kipling