Virtual Ammonites - Time Machines - page 160

paleontologists, he compiled and published massive monographic treat-
ments on his specialty. But unlike many of his colleagues, Westermann
began to wonder not only when his fossils lived but also how they lived. He
began to delve deeply into the structures and possible workings of these most
enigmatic of fossil invertebrates.
In 1971 Westermann published a landmark and revolutionary paper
about ammonite paleobiology. By incorporating newly available information
about the function of the nautilus shell based on breakthrough work con-
ducted by Eric Denton and John Gilpin-Brown in the mid-1960s, Wester-
mann proposed that the relative habitation depth of any ammonite could be
determined by a simple measurement of two parameters found within every
ammonite shell. Although the method did not reveal the actual measured
depth at which a given species of ammonite resided, it yielded the relative
depths of various ammonite taxa: that species A was capable of inhabiting
deeper water than species B, and that B lived deeper than C, and so on. A
corollary to this discovery was that those ammonites with the most complex
sutures generally showed the deepest depth ranges. All of the paleontologists
back to Buckland seemed vindicated. Ammonites with complex sutures
lived deeper than those with simpler sutures.
During the 1970s Westermann kept making discoveries that painted a
whole new picture of how these ancient creatures lived and "worked." He
used innovations, employed a variety of engineering techniques, and in pio-
neering fashion even co-authored a paper with a member of the engineering
faculty at his university. One of his findings was that ammonites with highly
complex septa had thinner septa than those with simpler morphologies—
and far thinner septa than any of the nautiloids, the supposedly most primi-
tive forms with the simplest septa of all, watch-glass-like structures slung
between the shell walls. There was only one snag in all of this: Nautilus,
with the simplest of septa, managed to live in very deep water. Nevertheless,
a general model seemed to be emerging. Ammonites evolved ever more
complex septa that were thinner than those with less complex morphologies.
Simple but strong septa would have to be very thick, and making thick septa