Hi Ellen and all,
Ammonites are not the ancestors of the modern Nautilus.  In fact, the
ammonites may have evolved from earlier nautiloid ancestors becoming a
separate group.  The ammonites, which were primarily shallow water
predators, became extinct at the end of the Cretaceous.  The nautiloids,
being deep water inhabitants, survived and evolved into the few modern
species we have today.

The major difference between ammonites and nautiloids is the position of the
siphuncle.  It is centered in Nautilus, but is located close to the outer
edge of ammonite shells.

John

John & Cheryl Jacobs
Seffner, FL
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