What are Belemnites?
Belemnites are the internal shells of an extinct type
of cephalopod mollusc related to modern octopus and
Like these living marine animals, they would have used
jet propulsion to chase their prey and to avoid being
eaten themselves by larger predatory animals such as
sharks and ichthyosaurs.
More complete belemnite fossils preserve not
only the pointed guard made of the resistant mineral
calcite, but also the fragile, chambered part of the
shell called the phragmocone, which
is made of the mineral aragonite. The crushed phragmocone
can be seen fitting within a conical depression in the
blunt end of the guard in this sectioned example.
Because of its close similarity to the chambered shells
found in other cephalopod molluscs, including the living
nautilus, the phragmocone provides crucial evidence
for the true biological affinities of belemnites.