the boundary. Peter writes in a book just published:
Finally, on a rainy day, I found a fragment of an ammonite within inches
of the clay layer marking the boundary. Slowly, over the years, several
more were found in the highest levels of Cretaceous strata at Zumaya.
Ammonites appeared to have been present for Armageddon after all.
Peter then took the obvious next step: look elsewhere. Zumaya contained
ammonites right up to the end, but not copiously, perhaps for masons of
local habitat rather than global abundance. Peter had looked in sections
west of Zumaya and found no latest Cretaceous ammonites (another reason
for his earlier acceptance of gradual extinction). But now, he extended
his fieldwork to the east, toward the border of Spain and France. (Again,
these eastern sections were known and had always been available for study,
but Peter needed the impetus of Alvarez to ask the right questions and
to develop a need for making these further observations.) Peter studied
two new sections, at Hendaye on the Spanish-French border and right on
the yuppie beaches of Biarritz in France. He found an abundance of ammonites
just below the boundary line of the great extinction. He writes in his
new book:
After my experience at Zumaya, where years of searching yielded only
the slightest evidence. . .near the Cretaceous-Tertiary boundary, I was
overjoyed to find a source of ammonites within the last meter of Cretaceous
rock during the first hour at Hendaye.
We professionals may care more about ammonites, but dinosaurs fire the
popular imagination. No argument against Alvarez has therefore been more
prominent, or more persuasive, than the persistent claim by most (but
not all) dinosaur specialists that the great beasts, with the possible
exception of a straggler or two, were gone long before the supposed impact.
I well remember the dinosaur men advancing their supposed smoking gun
of a "three-meter gap"--the barren strata between the last-known
dinosaur bone and the impact boundary. And I recall Luis Alvarez exploding
in rage and with ample justice (for I felt a bit ashamed of my paleontological
colleagues and their very bad argument). The last bone, after all, is
not the last animal, but rather a sample from which we might be able to
estimate the probable later survival of creatures not yet found as fossils.
After all, if my colleague throws a thousand bottles overboard and I later
pick up one on an island fifty miles away, I do not assume that he only
tossed a single bottle. But if I know the time of his throw and the pattern
of currents, I might be able to make a rough estimate of how many he originally
dropped overboard. The chance of any animal becoming a fossil is surely
much smaller than the probability of my finding even one bottle. All science
is intelligent inference: excessive literalism is a delusion, not a humble
bowing to evidence.
Again, as with Peter Ward and the ammonites, the best empirical approach
would order a stop to the shouting and organize a massive effort to dismember
the haystack by looking for dinosaur bones in every inch of latest Cretaceous
rocks. Peter means "rock" in Latin, so maybe men of this name
are predisposed to a paleontological career. Another Peter, my friend
and colleague Peter Sheehan of the Milwaukee Public Museum, has been guiding
such a project for years. Just last month (I write this essay in December
1991), he published his much awaited results (see "Sudden
Extinction of the Dinosaurs: Latest Cretaceous, Upper Great Plains, U.S.A.,"
by P M. Sheehan, D. E. Fastovsky, R. G. Hoffmann, C. D. Berghaus, and
D. L Gabriel, Science, November 8, 1991, pp. 835-39).
Dinosaurs are almost always rarer than marine creatures, and this haystack
really has to be pulled apart fragment by fragment and over a broad area.
The National Science Foundation and other funding agencies simply do not
supply grant money at such a scale for projects that lack experimental
glamor, whatever their importance. So Peter (Sheehan this time) availed
himself of a wonderful resource that mere ammonites could never command.
I will tell this story in his words:
We co-opted the longstanding volunteer-based "Dig-a-Dinosaur"
program at the Milwaukee Public Museum. Sixteen to 25 carefully trained
and closely supervised volunteers and 10 to 12 staff members were present
during each of 7 two-week field sessions during three summers. The primary
objective of each volunteer was to search a predetermined area for all
bone visible on the surface. The volunteers were arrayed in "search
party" fashion across exposures so that all outcrops were surveyed
systematically. Associated with the field parties were geologists whose
function was to measure stratigraphic sections and identify facies.
I cannot think of a more efficient and effective way to tackle a geological
haystack. Peter's personnel logged 15,000 hours of fieldwork and have
provided our first adequate sampling of dinosaur fossils in uppermost
Cretaceous rocks. They worked in the Hell Creek Formation in Montana and
North Dakota, the classic strata for latest Cretaceous dinosaurs. They
studied each environment separately, with best evidence available from
stream channels and floodplains. They divided the entire section into
thirds, with the upper third extending right up to the impact boundary,
and asked whether a steady decline occurred through the three units, leaving
an impoverished fauna when the asteroid struck. Again, I will let their
terse conclusion, summarizing so much intense effort, speak for itself:
Because there is no significant change between the lower, middle, and
upper thirds of the formation, we reject the hypothesis that the dinosaurian
part of the ecosystem was deteriorating during the latest Cretaceous.
These findings are consistent with an abrupt extinction scenario.
You can always say, "So what; T. S. Eliot was wrong; some worlds
at least end with a bang, not a whimper." But this distinction makes
all the difference, for bangs and whimpers have such divergent consequences.
Peter Ward sets the right theme in his final statement on the non-necessary
demise of ammonites:
Their history was one of such uncommon and clever adaptation that they
should have survived, somewhere, at some great depth. The nautiloids did.
It is my prejudice that the ammonites would have, save for a catastrophe
that changed the rules 66 million years ago. In their long history they
survived everything else the earth threw at them. Perhaps it was something
from outer space, not the earth, that finally brought them down.
The true philistine may still say, "So what; no impact and we still
have both ammonites and nautiloids. What do I care. I had never even heard
of nautiloids before reading this essay." Think about dinosaurs and
start caring. No impact to terminate their still-vigorous diversity and
perhaps they survive to the present. (Why not? They had done well for
more than 100 million years, and the earth has only added another 66 million
since then.) If they survive, mammals almost surely remain as small and
insignificant as they were during the entire 100 million years of dinosaurian
domination. And if mammals stay so small, restricted, and unendowed with
consciousness, then surely no humans emerge to proclaim their indifference.
Or to name their boys Peter. Or to wonder about the heavens and the earth.
Or to ponder the nature of science and the proper interaction between
fact and theory. Too dumb to try and too busy scrounging for the next
meal and hiding from that nasty Velociraptor.
Stephen Jay Gould teaches biology, geology, and the history of science
at Harvard University.
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