University of Bristol logo Fossil group banner, with title and coposite picture of fossils


Belemnites


Belemnites are known from the Jurassic and Cretaceous. In the typical genus Belemnites the shell has three parts; the guard is the largest and most posterior of these. It is solid calcite and forms a massive bullet-shaped cylinder, which tapers posteriorly to a point. The surface of the guard is usually smooth but can be granular or pitted, while the anterior end is indented by a conical cavity called the alveolus. The second part of the shell is the phragmocone and this lies within the alveolus. This is homologous to the nautiloid shell and has a slender siphuncle that threads through the septa at the ventral margin. The pro-ostracum is the third component and is a long flat expanded tongue that projects forwards and protects the anterior part of the body. However this is rarely preserved.


Argonautidae
Major Subclasses
Return to index page
Websites produced by students on the MSc Palaeobiology programme in the Department of Earth Sciences at the University of Bristol for academic year 2004-5