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global catastrophe. But which ones, and how many? Was it some distant an-
cestor of our familiar chambered nautilus (technically Nautilus pompilius)! Or
was it the very same species that is living today, whose shells can be pur-
chased in any curio or shell shop? And did only a single nautiloid survive, or
might several types (either several species or higher taxonomic groupings,
such as several genera or even several families) have dodged the bullet of this
mass extinction? Even several years ago, paleontologists who study the fossil
record of shelled cephalopods (which include the ammonites and nautiloids)
would have told you that the nautiloid cephalopods living in the Cretaceous
were only distant ancestors of the Nautilus of our world, in the same way that
early apes are related to humans.
According to this evolutionary hypothesis, the single genus Nautilus,
with its four or five living species, is the sole surviving remnant of this ancient
group. Increasingly, however, this time-honored view of cephalopod evolution
appears to be a hypothesis that must be rejected. New methodologies (such as
advances in DNA sequencing techniques and a new way of tracking the course
of evolution called phylogenetic systematics (also known as cladism, it is de-
scribed in more detail below) and recent discoveries of previously unknown
living and fossil nautiloid specimens have drastically changed our understand-
ing of these ancient animals. Our current knowledge would have been paleon-
tological heresy even a decade ago: The nautilus not only dates back to (and
lived through) the great K/T calamity but also became the rootstock for an
evolutionary radiation of new nautiloid genera in the ensuing Cenozoic Era.
And (heresy of heresies!) our world is graced with not one but two genera of
living nautiloid cephalopods. How we arrived at these new understandings is
perhaps as fascinating as the animal itself, for the recent elucidation of the
nautilus's great feat of survival—it has lasted at least 100, and perhaps 200, mil-
lion years—is a saga of how science often works. It frequently progresses in fits
and starts, is shaped the influence of forceful personalities and chance discov-
eries, and is hampered by many decades of mistaken identity.
The pearly nautilus, with its spiraled, chambered shell, is often grouped
with the coelacanth, the opossum, and the dragonfly as living fossils—
archaic creatures that have somehow survived to the present. In Charles
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