Travel Reference
In-Depth Information
cephalopods—is through the disciplines of systematics and taxonomy. Com-
bined, they are another powerful type of time machine.
The story of how the nautilus has been classified is an example of how
these particular time machines operate. It is detective work, and as the work
progresses and the family tree is discerned, one feels great satisfaction, fot
any view of a family tree always brings new knowledge and a new perspective
on the past.
Imagine that you
did
have access to a time machine capable of whisk-
ing you (along with a good set of scuba gear) back to the last days of the
Mesozoic Eta—to 65 million years ago, just before the asteroid strike that
was to end the Age of Dinosaurs. What would you see? On land, of course,
you would sooner or later encounter dinosaurs in great variety and profusion.
But in the sea, would it be as immediately apparent that you were not in our
time, that you were indeed back in the Mesozoic Era? Actually, as you settled
onto a Cretaceous sea bottom 50 feet deep, it might be even more apparent
that you had arrived in a foreign, long-ago place, for in any Cretaceous ocean
you would quickly encounter a fantastic assemblage of large, alien-looking
shelled cephalopod mollusks acting and swimming like fish. By the Mesozoic
Era, the chambered cephalopods were already ancient. As the first latge,
swimming carnivores in the world's oceans, they have been among the domi-
nant marine predators for much of the last 500 million years; there are over
10,000 known fossil species. Ranging in shell size from less than an inch to
mote than 12 feet across, and in shape from coiled to straight to elabotate,
candy-cane contraptions, the great armored dreadnoughts of the Mesozoic
world that you would see would be of two kinds: ammonites and nautiloids.
The former, by far the more abundant and diverse of the two groups, would
be easily distinguishable by their more ornate shells and peculiar shapes. But
the latter, more conservative group, bereft of the rococo ribs and spines,
keels, and knobs that characterize the ammonite lineage, would look quite
familiar to most of us. Who has not seen the shell of the nautilus?
Following the 65-million-year-old Chicxulub comet impact (the
"K/T" extinction), all of the ammonites (like the dinosaurs on land) were
quickly exterminated. Yet there were nautiloids that survived this great
