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Embargoed until 2 p.m. Eastern Time
NSF PR 03-57 - May 15, 2003
Fossil Record Accurately Reflects Recent Flowering of Marine Biodiversity
Arlington, Va.-The apparent increase in marine biodiversity over
the past 50 million to 100 million years is real and not just a
false reading produced by the inconsistencies of the fossil
record, says a team of paleontologists led by the University of
Chicago's David Jablonski. This finding, published in the May 16
issue of the journal Science, may help scientists place the
future of global biodiversity in its proper context.
"If you want to understand what's going to come in the future you
need to understand the dynamics that led up to the biodiversity
we see now," said Jablonski.
By some measures, up to 50 percent of the increase in marine
animal biodiversity during the past 50 million years can be
attributed to what paleontologists call "the Pull of the Recent."
This is the idea, posed in 1979 by University of Chicago
paleontologist David Raup, that the level of biodiversity is
inflated in younger fossil deposits because sampling of the
modern world is so much more complete than in the geologic past.
But the Pull of the Recent accounts for as little as 5 percent of
the biodiversity increase, at least for one well-preserved group.
"The results of this exciting study show how a thorough
understanding of deep-time biotas and diversity places modern
life into the correct perspective and provides a predictive
capability for the future," said H. Richard Lane, director of the
National Science Foundation (NSF)'s paleontology program, which
funded the research. "These results can be applied to the study
of natural processes and climate cycles in deep time, relating
that to the modern situation, and using that knowledge to predict
the future."
Scientists have long believed that diversity proliferated
dramatically after the Paleozoic Era, which ended 250 million
years ago, to the late present day. The work of James Valentine
of the University of California, Berkeley, and a co-author of the
Science article, pointed to a 10-fold increase.
Joining Jablonski and Valentine on the project were Kaustuv Roy,
University of California, San Diego, and University of Chicago
graduate students Rebecca Price and Philip Anderson.
The team studied bivalves (clams, scallops, oysters and mussels)
to address the issue because they are one of the major
contributors to marine animal biodiversity. In order to screen
out a potential false reading for Cenozoic biodiversity, the team
inventoried bivalve diversity in the youngest part of the
geologic record. This would allow for assessment of the impact of
the living bivalves by ignoring the biodiversity in modern oceans
and building a diversity history based only on the fossil
occurrences.
"This involved churning through a massive amount of the published
paleontological literature of marine bivalves that lived during
the last five million years," Jablonski said.
Complicating the task were the nomenclature changes that affected
some types of bivalves. A single species might have been
classified differently in each of four different papers published
during the last 100 years as paleontologists' understanding of
its evolutionary relationships improved, Jablonski said. Once the
team members had standardized the classifications, they found
that 906 of the 958 types (95 percent) of living bivalves they
examined left a fossil record within the past 5 million years, as
well as earlier in many cases.
The possibility still existed that rocks deposited 5 million
years ago were unusually rich and that they were distorting the
fossil record. So the team conducted a second inventory of
bivalves that plunged much deeper into the fossil record, back 65
million years ago to the days of the dinosaurs. The
paleontologists still were able to recover 87 percent of the
types of bivalves that lived through that interval, when some
thought the record might be poorer. The high recovery rate
supports claims that the lower diversity levels observed from
this time are genuine and not artificially depressed by sampling
or preservation.
"Skeptics would say, well, that's just bivalves. Maybe they're
somehow unique," Jablonski said. But a similar recovery figure,
89 percent, applies to sea urchins, which researchers at London's
Natural History Museum inventoried for the same period.
"We've been talking about putting together a consortium of people
to do exactly this kind of study with essentially all the major
groups that make up the biodiversity increase," Jablonski said.
"It'd be a real boon for the field if we can get this under way,
because it will simultaneously tackle the sampling question and
put a huge chunk of the fossil record into a standardized
evolutionary framework."
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