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Chambers to the Past
| Article
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14920 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
10 / 1988 |
1,372 Words |
| Author
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Peter Douglas Ward
Peter Douglas Ward is professor of geological sciences at the
University of Washington. He has been investigating the late
Mesozoic extinction for over a decade, both documenting the
ranges of species that became extinct and studying the
survivors of this crisis. His most recent book, The
Methuselahs, dealing with the survivors of mass extinction,
will be published by the W.H. Freeman Company in September. |
When European civilization emerged from the Dark Ages, it began to send ships off to ever more distant shores. When and if these ships returned, they brought back unbelievable stories of strange men and creatures and lands. And sometimes they brought back treasures from these distant worlds. Three such treasures especially excited the Renaissance mind: the ostrich egg, the coconut, and the nautilus shell.
The nautilus shell is familiar to us all. Much less so is the creature that produced this wonder. We have marveled at its design, appreciating the difficulties and potentialities represented by such a construction. But the nautilus is far more than a beautiful creature. It is a link to the past, one of the earth's great survivors.
Nearly a decade after the celebrated meteoric hypothesis of the Alvarezes and their colleagues, the debate still rages over the causes of the great mass extinction occurring at the end of the Cretaceous period, some 66 million years ago. Yet, even if the cause is still unclear, be it meteoric impact or some international cause inherent in the earth such as rapid temperature or seal-level change, no one doubts that great mass extinctions occurred several times in the earth's past. During these short-lived events, significant percentages of the earth's biota disappeared. [See "The Mass Extinction Controversy," THE WORLD & I, Jan. 1988, pp.162-71.]
The major focus of scientific research dealing with the mass extinctions has classically dealt with those animals that died. But a recent trend among the paleontological specialists studying these intervals of mass death has been to focus on those that survived, rather than those that did not. Dinosaurs were certainly wondrous creatures, but perhaps there is more to be learned from the few species that survived the holocaust: the living, rather than the dead, are the objects of increasing scrutiny.
The nautilus is one such survivor. But this shellfish, so familiar to us in name and shape and yet so rarely seen alive, has a noble heritage. The nautiloids evolved from rather primitive snail-like mollusks early in the Paleozoic era, about 500 million years age, and had the distinction of being the first large carnivores and subsequent diversification of the nautiloids is a text-book example of the potentialities of the evolutionary process.
Nautiliods became so when they evolved a method of moving their fleshy body parts out of the back portions of
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