Ammonites
An ammonite is an extinct inkfish-like animal with chambers in its shell. The order of Ammonidea belongs to the class of inkfish like animals (Cephalopoda) and the phylum Mollusca. The name comes from the Egyptian god Ammon. Ammonites look like the curled rams horns which depicted Ammon.
The shell was made of aragonite, and mostly the shell itself is not fossilized. Small ammonites occasionally are completely made of pyrite. Ammonites were free swimming animals in the oceans. They could regulate there depth by pumping nitrogen gas in the old chambers of its shell. The chambers are connected with a "sipho" in which the gas was transported from the body fluids.
The size of ammonites varies between less than a centimetre to 2.5 metres diameter! Many species of ammonites existed. Most ammonites were winded, but also unwinded ammonites occurred.
The chambers of the ammonite are separated by complex "suture lines". Ammonites first occur in upper Silurian period. They became extinct at the end of the Cretaceous period. The only living family member is the nautilus .
Ammonites have evolved quickly in the course of history. Together with the fact that they fossilize very well, makes them perfect guide fossils. The stratigraphy of the Mesozoic is largely bases on the occurrence of certain species of ammonites. Especially in the Jurassic and Cretaceous periods the ammonites were abundant.
Example of an Ammonite.
Description of the suturelines occurring in goniatites, ceratites and ammonites.
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 Go to the Photo page to view photographs of Ammonites. |
