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Mollusca: Cephalopoda: Ammonoidea

Picture of Ammonoidea: Lytoceras fimbratum Black and white drawings of various ammonoid forms Picture of Ammonoidea: Descophyllities ebneri
Outer pictures are of Kerberites giganteus and Lytoceras fimbriatum taken with permission of the University of Bristol.
Centre plate displays a variety of ammonoid forms by Ernest Haeckel (1899) in his work Artforms of Nature (source: wikipedia).

The Cephalopods are the most advanced and complex form of the phylum mollusca; they have roamed the seas since the upper Cambrian 500 million years ago and can still be found in all the worlds' oceans today.

The Class cephalopoda can be separated into three subclasses consisting of:
Nautiloidea (Cambrian – Recent) e.g. nautilus
Coleoidea (Carboniferous – Recent) e.g. squid, cuttlefish, octopuses
Ammonoidea (Devonian – Cretaceous) e.g 

The Ammonoidea is the only extinct subclass of cephalopods, it was wiped out during the Cretaceous–Tertiary (K-T) mass extinction 65 million years ago.  Its wide distribution in specific environments and speed of evolution make it an ideal zone fossil. The high preservation potential of the ammonoid shell and relative abundance make its appearance in the sedimentary record invaluable for palaeoenvironmental and palaeobiological research. 

Author: Nick Loughlin
Last updated: 18/11/06
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