Ammonite Goniatite

AMMONITE–AN EXTINCT SUBCLASS OF THE CEPHALOPOD CLASS OF THE PHYLUM MOLLUSCA (Mollusks). Present-day cephalopods include the octopus, squid and nautilus, which is the closest in appearance to the ammonite. Ammonites ranged in time from approximately 400 million years(Devonian) until about 65 million years.(late Cretaceous). Their chambered shells are found today, while their soft bodies, which occupied the largest and outermost chambers, are gone. The septa, plates which divide the chambers, are highly visible in cut fossilized ammonite specimens.

Ammonites had a tube called a siphuncle, which carried water from outside the shell to the chambers, and was used to propel the ammonite as well as to change its depth in the water. Cephalopods, such as the ammonite, were swimming mollusks, rather than attached (pelecypods) or bottoms dwelling(gastropods) mollusks.

The ammonites showed an increasingly complex pattern of sutures on their shells as time went by. Sutures are the intersections of the septa and the outer shells.

Ammonite shells: originally composed of aragonite; after fossilization, the shell
becomes calcite.
Ammolite: some of the original shells retained their mother of pearl nacre over the centuries, which during fossilization, was chemically transformed into an iridescent material called ammolite (aragonite with varying
mineral impurities).
Localities: include Russia, England, Morocco, U.S., and Madagascar.