"New York Times"
May 22, 2001
Fossil Findings May Force Revisions in the History of Life
By CAROL KAESUK YOON

After the most devastating mass extinction swept the planet 250 million
years ago, the earth witnessed a nearly unabated increase in the variety of
living organisms leading to unparalleled heights of diversity or so
paleontologists have long thought.

Now a new study in The Proceedings of the National Academy of Sciences
suggests a radically different picture that, if correct, will require a
large-scale rewriting of the history of life.
In the first results from a huge new database of fossil records being
assembled on the World Wide Web by an international team of scientists,
researchers report findings that suggest there may have been no such
relentless increase in diversity. In fact, the new results suggest the
possibility that diversity levels quickly hit a plateau and stayed put and
that the real peak of life's diversity may have come and gone more than 400
million years ago.

But scientists, including the authors, cautioned that the results should be
viewed as preliminary. Even though the new study addresses what some feel
are critical flaws in the previous work showing steep increases in
diversity, scientists note the results are a first look at a complex new
database.

The current study focuses on fossil marine organisms, but scientists plan
to include records of fossils of all kinds from the span of the history of
life on earth in the database (flatpebble.nceas.ucsb.edu/public) at the
National Center for Ecological Analysis and Synthesis, which supported much
of the work.

But while adopting a wait-and-see attitude, scientists outside the study
acknowledged that if true, the findings would require a radical rethinking
of not only when diversity levels rose and fell, but why.
"This calls into question longstanding views of the diversity of life,"
said Dr. Douglas Erwin, a paleobiologist at the Smithsonian Institution,
adding it was too soon to draw firm conclusions. But he said, "It's very
exciting for paleontology."

For example, the many theoretical explanations for the steady increase in
diversity would become irrelevant and a whole new series of questions about
the relative constancy in levels of diversity would emerge.
"This is a very important enterprise," said Dr. Jeremy Jackson,
paleobiologist at Scripps Institution of Oceanography, though he was highly
skeptical of the new work. "If it were true, the implication would be that
there was some sort of ceiling on diversity, something limiting it, which
would be fascinating."

It was the pioneering work of Dr. J. John Sepkoski, a paleobiologist at the
University of Chicago, who died in 1999, that provided the first evidence
that diversity had been on a steady climb (with occasional minor setbacks
like the extinction that took the dinosaurs) ever since the mother of all
extinctions, known as the Permo- Triassic. Similar studies of plants,
insects and other animals followed and showed the same unending rise in the
variety of forms of life.

But there have always been nagging doubts. As it turns out, counting up
what different kinds of fossil organisms lived in any particular time
period is not as simple as it may sound. Because researchers draw on the
many published studies of fossils done over the years to fill their
databases, among the thorny problems is the fact that scientists have
studied some areas with much greater intensity than others.

In one example of true paleontological zeal, Dr. G. Arthur Cooper, a
paleobiologist at the Smithsonian Institution, led a 40-year effort
collecting more than 100,000 fossil specimens from the Glass and Guadalupe
Mountains in West Texas. The fossils, which are naturally made of glass,
include the clamlike marine organisms known as brachiopods.
Dr. Cooper, who died recently, "wanted to find every last species of
brachiopod," Dr. Erwin said.

Yet information from such exhaustive surveys from one time and place would
be compared with information from much more superficial surveys, which
would have missed most of the rarer species, from other time periods around
the world.

Even more problematic is the fact that newer rocks and fossils are easier
to get at and have been much more intensively studied by paleontologists.
So as scientists tally the organisms discovered in more than a century of
paleontological research, they will necessarily find a much greater
diversity of newer organisms than older ones, whether they were actually
more abundant in reality or not.

But even with consideration of the acknowledged problems, scientists said
the consensus remained that the increase in diversity was real.
Dr. John Alroy, paleobiologist at the National Center for Ecological
Analysis and Synthesis at the University of California at Santa Barbara,
and Dr. Charles Marshall, paleobiologist at Harvard, are the first two
authors on the 25-author paper in which researchers tried to get around
some of the problems by making a variety of statistical attempts to sample
fossil species equally from the different periods of time. The paper is
dedicated to Dr. Sepkoski, who is also an author on the study.
The result is a variety of possible chains of events for how diversity
waxed and waned, all different from the standard view, but all indicating
that the steep increase in diversity seen in previous studies may have been
influenced by the bias in information about newer fossils.

Scientists note also that the new study has its own biases. For example,
the study focuses on marine organisms from around North America and Europe,
and a different pattern could emerge as the database gains more geographic
breadth.

"The data's got a lot of dimensions, and there are a whole range of things
to be done," said Dr. Marshall, who said confidence versus wariness over
the new results varied greatly even among the 25 authors. He added, "We
ain't there yet."

And even as paleontologists applauded the Herculean efforts to work on this
bigger, better database, some suggest the approach itself may be flawed.
Some including Dr. Jackson say researchers may be better served by getting
out of the library and into the field, doing new fossil surveys. Rather
than fighting biases in data collected 100 years ago for other purposes,
they could collect the most appropriate data in a uniform and comparable way.
Likely to continue to spur as much criticism as support, the analyses of
the new database go on.

"I hope they're right," Dr. Erwin said of the new findings, "because life
will be more interesting for the next 10 or 20 years if they are. We'll
have to re-examine a lot of assumptions."

POWRÓT