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 ammonites
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.
