Travel Reference
In-Depth Information
Sudden loss of buoyancy is certainly fatal to a nautilus. In most places
where it lives, the surface of the sea is simply too warm for a nautilus to live.
Surely, there must be numerous adaptations—such as rapid chamber
refilling—to compensate for this hazard. But there are not! The rate of refill-
ing in a nautilus is very slow. And that characteristic, which I discovered in
the mid 1980s, may be a clue to why ammonites evolved more complicated
sutures.
Tom Daniel has looked at this problem and has concluded that the
complications of septa within the chambered cephalopod shell would favor
the
readmittance
of water to an already emptied chamber. Because of surface
tension properties, such complications actually make it easier for an am-
monite to refill chambers. Because any bite by a predator would cause a sud-
den
increase
in buoyancy, this type of adaptation would be selected for. It is a
simple and elegant solution. Ammonites with more complicated sututes
would be better able to refill chambers rapidly—and thus become less
buoyant—following a predatory attack. As ever more predators evolved in
the Mesozoic world, including a whole army of new types of shell-breaking
predators, ammonites "retaliated" by evolving ever more elegant and sophis-
ticated ways of compensating for sudden buoyancy. If our view is correct,
that meant more complicated sutures.
Microcomputers have thus transported us back into Mesozoic oceans.
They have served as powerful time machines.
Where are they now, these elegant ammonites? Could not a few, at
least, still grace our planet? Sadly, I know the answer to that question. They
are gone, long gone, never to be resurrected, driven into extinction by the
collision of a giant comet with the earth 65 million years ago. But some ves-
tige of them persists in the fertile imaginations of a few paleontologists, for
surely I am not alone in contemplating deep, calm bottoms where these an-
cient creatures evolved structures whose startling regularity and grace so
long haunted my dreams.
