Phylum: Mollusca
Class: Cephalopoda
Subclass: Coleoidea
Cohort: Belemnoidea
Diagram with labelled features of belemnites
'Bullet' shape
Phragmocone: chambers divided by aragonitic septa (often preserved as conical cavity)
Radial calcite crystals form the guard
Nektonic
Predatory
Marine
Exceptional preservation of belemnites showing soft parts has shown them to be very similar to squid in shape. The guard and phragmocone were held inside the soft parts of the animals, acting as a kind of backbone.
Because the phragmocone is made of aragonite it is often not preserved. In contrast the calcitic guard is very often preserved. This means that a common preservation of belemnites is of the guard with a conical hole where the phragmocone once was. This empty conical chamber is often crushed.
Phylum: Mollusca
Class: Cephalopoda
Subclass: Coleoidea
Cohort: Belemnoidea
Diagram with labelled features of belemnites
'Bullet' shape
Phragmocone: chambers divided by aragonitic septa (often preserved as conical cavity)
Radial calcite crystals form the guard
Nektonic
Predatory
Marine
Exceptional preservation of belemnites showing soft parts has shown them to be very similar to squid in shape. The guard and phragmocone were held inside the soft parts of the animals, acting as a kind of backbone.
Because the phragmocone is made of aragonite it is often not preserved. In contrast the calcitic guard is very often preserved. This means that a common preservation of belemnites is of the guard with a conical hole where the phragmocone once was. This empty conical chamber is often crushed.
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
[See labelled diagram above]
Aragonite shell
Septa
Suture (different for goniatites, ceratites and ammonites, see second diagram above)
Chambers
Siphuncle
Planispiral shape, involute or evolute (see third diagram on right hand side)
Devonian to Cretaceous
Nektonic (jet propelled)
Predatory
Marine
Internal mould
Learn about types of preservation
Ammonoids could passively remove or add water to chambers via the siphuncle. This allowed them to change their density, and maintain neutral buoyancy with the surrounding seawater. This meant that they were able to swim as efficiently as possible.
Ammonoids are extremely good index fossils on account of their diverse morphologies, good preservation potentials and widespread fossil locations.
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
[See labelled diagram above]
Aragonite shell
Septa
Suture (different for goniatites, ceratites and ammonites, see second diagram above)
Chambers
Siphuncle
Planispiral shape, involute or evolute (see third diagram on right hand side)
Devonian to Cretaceous
Nektonic (jet propelled)
Predatory
Marine
Internal mould
Learn about types of preservation
Ammonoids could passively remove or add water to chambers via the siphuncle. This allowed them to change their density, and maintain neutral buoyancy with the surrounding seawater. This meant that they were able to swim as efficiently as possible.
Ammonoids are extremely good index fossils on account of their diverse morphologies, good preservation potentials and widespread fossil locations.