[meteorite-list] Were the Dinosaurs Done in by Fungus?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Feb 23 16:15:45 2005
Message-ID: <200502232115.j1NLFSE29539_at_zagami.jpl.nasa.gov>

http://www.boston.com/news/globe/health_science/articles/2005/02/22/were_the_dinosaurs_done_in_by_fungus/

Were the dinosaurs done in by fungus?
By Carolyn Y. Johnson
The Boston Globe
February 22, 2005

In the still unsolved mystery of how the dinosaurs died, there's a new
suspect -- fungus.

After a meteor slammed into the Earth 65 million years ago, "the great
dying" began, decimating life in the oceans and killing off the
dinosaurs -- with mysteriously little effect on mammals. Conjecture over
what did in the reptiles has long fascinated everyone from school
children to paleontologists, but a new theory suggests that a less
earth-shaking possibility could have played a role.

"The forests went out. The fungi proliferated, and the Earth became a
giant compost pile. An enormous number of spores were released," said
Dr. Arturo Casadevall, an infectious disease researcher who proposed
last month that air thick with fungal spores after the meteor hit could
have overwhelmed animals' immune systems, causing sickness and death. If
he's right, the large numbers of warm-blooded mammals and birds that
survived the mass extinction might have had a natural advantage -- body
temperatures too hot for fungal infections to take hold.

"It's just a beautifully creative suggestion," said Nicholas Money, a
mycologist, or mold expert, from Miami University of Ohio and author of
"Carpet Monsters and Killer Spores: A Natural History of Toxic Mold."

Casadevall, of Albert Einstein College of New York, laid out his
suggestion in this month's issue of Fungal Genetics and Biology when
considering a much larger question: "I ask you, why are we so hot?"

He has long been troubled by the lives of warm-blooded animals, who must
live a virtual food-finding mission because they burn so many calories
each day just heating their bodies. Cold-blooded animals, on the other
hand, need only eat once every few days. Where, he wondered, is the
advantage in a life of constant scurrying, foraging, and saving up food
for the winter?

That question coincided with another puzzling trend: Fungal infections
rarely give mammals more than a mildly irritating case of athlete's foot
or a yeast infection but are often deadly to plants, fish, and insects.

At a crucial time in natural history, the world's 1.5 million species of
molds, yeasts, rusts, and mushrooms, also might have been a vehicle for
natural selection.

In the aftermath of the meteor that carved out the Chicxulub crater on
the Yucatan Peninsula, the Earth probably was a cool, shady place.
Researchers last year discovered fossil evidence of a post-collision
"fungal spike," and in a world dense with potentially pathogenic fungi,
warm-blooded animals might have had a unique advantage.

In such a situation, "every warm-blooded generation has a little
advantage, and when the dust settles and the sun comes out again . . .
the warm-blooded find themselves in a world with a lot more space,"
Casadevall said.

Other evidence shows that the mass die-off didn't occur immediately
after the collision, but about 300,000 years afterward -- raising the
possibility that an intermediary factor, like fungi, could have played a
part.

The trouble with the theory, experts said, is that no one is sure
whether the dinosaurs were warm- or cold-blooded. Smaller cold-blooded
animals like turtles, lizards, snakes, and frogs were able to weather
the mass extinction, indicating that size, not body temperature, may
have been a deciding factor.

And, while there is wide agreement that a massive meteor struck the
Earth 65 million years ago, other theories suggest that increased
volcanic activity could have played a role in the extinction.

Stephen McLoughlin, a geologist from Queensland University of Technology
in Australia who discovered evidence of the long-ago fungal explosion,
said the spores that his group studied, which were preserved in a layer
of coal in New Zealand, probably did not harm animals.

He stated in an e-mail that he finds Casadevall's idea "intriguing" but,
"while this may have been the case, it is virtually impossible to test."

Nonetheless, the main idea behind Casadevall's research -- that deadly
fungi could have helped establish the age of the mammals -- is timely.

Fungal infections are now emerging as an important force in nature
again: Fungal diseases also may be contributing to the worldwide decline
of the coral reefs, and appear to play a poorly understood role in the
steady decline of amphibians.

A study last year reported that a third of all amphibian species
worldwide are facing extinction -- and while climate change, pollution,
and habitat loss are all thought to play a role, many of the extinct and
endangered frog species have been infected with the chtyrid fungus,
which may interfere with their delicate, breathable skin, produce a
toxin, or something else.

"Like everything in life, it wasn't just one thing" that killed the
dinosaurs, Casadevall said. In the case of the amphibians, "you can
imagine [the culprit] could be a weakening of their immunity caused by a
fungus."
Received on Wed 23 Feb 2005 04:15:28 PM PST