The ammonites (Order Ammonoidea) are an extinct group in the phylum Mollusca and class Cephalopoda. These animals first appeared in the Devonian Period and became extinct at the close of the Cretaceous along with the dinosaurs. The closest living relative of the ammonites is the modern Nautilus. These creatures had a hollow chambered shell most often coiled. A few types do not have this regular form of coiling (these are called heteromorphs). A couple of examples can be seen in the specimens photographed below. Exiteloceras has a low coiled (some other genera are high coiled), loosely spiraled shell (some may be tightly spiraled). Baculites and Sciponoceras are straight ammonites with a small initial coil. Ammonite shells can be very smooth to those with high ornamentation (ridges, nodes, tubercles). Classification of ammonites is, in part, based on this ornamentation and structure of the septum (partitions dividing the chambers). The suture patterns derived from the shape of the septa define the division of this order into the eight known suborders. Here they are listed from most primitive to more advanced: Anarcestina (Devonian only), Clymeniina (Upper Devonian only), Goniatitina (Devonian to Upper Permian), Prolecanitinahotel a Malaga (Upper Devonian to Upper Triassic), Ceratitinaalberghi a Lyon (Permian to Triassic), Phylloceratina (Lower Triassic to Upper Cretaceous), Lytoceratina (Lower Jurassic to Upper Cretaceous), and Ammonitina (Lower Jurassic to Upper Cretaceous).

 
Illustration by D. S. Norton from Ammonites and the Other Cephalopodsof the Pierre Seaway by Neal Larson, Steven Jorgensen,Robert Farrar, and Peter Larson; Geoscience Press, 1997

barcelohotel SopotAmmonite background information provided by Andrew R. Milner;
Hanman's Fossils and Minerals
info@hanmansfossils.com   http://www.hanmansfossils.com