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Belemnites:

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belemnite - phragmocone

What are Belemnites?

Belemnites are the internal shells of an extinct type of cephalopod mollusc related to modern octopus and squid.

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.

Structure
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.

   
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