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Belemnites (or belemnoids) are an extinct collection of marine cephalopod, very parallel in many ways to the modern squid and closely related to the modern cuttlefish. Like squid and cuttlefish, belemnites had an ink sac, but dissimilar the squid, they have no tentacles. Instead, they possessed ten arms of approximately equal length. Unlike the contemporary squid, whose arms have suckers, belemnite arms carried a series of little hooks for grabbing prey.

Belemnites were well-organized carnivores that caught small fish and other marine animals with their arms and ate them with their beak-like jaws. In turn, belemnites emerge to have formed part of the diet of marine reptiles such as Ichthyosaurs, whose fossilized stomachs regularly contain many phosphatic hooks from the arms of cephalopods.

Belemnites were many during the Jurassic and Cretaceous periods and their fossils are plentiful in Mesozoic marine rocks where they are joined by their cousins, the Ammonites. They originated during the Devonian age and well-formed belemnite guards can be found in rocks dating from the near the beginning Carboniferous period onward through to the Cretaceous age. Towards the end of the Cretaceous period, Belemnites became extinct along with Ammonites.

Usually with fossil belemnites, only the back part of the shell (called the guard or rostrum) is found. The guards is bullet-shaped and elongated and are curved and pointed at one end. The hollow region at the front of the guard is termed the alveolus and this houses a chambered conical-shaped fraction of the shell (called the phragmocone). The phragmocone is regularly only found with the better preserved specimens. Projecting forwards from one side of the phragmocone is the thin pro-ostracum. The guard, phragmocone and pro-ostracum were all interior to the belemnite, forming a skeleton which was enclosed completely by soft muscular tissue. The belemnite would have been larger than the fossilized shell, with a long streamlined body and famous eyes. The guard would have been in place toward the rear of the belemnite, with the phragmocone behind the head and the sharp end of the guard facing backward.

The guard of the belemnite, which is found in Europe and Asia, can gauge up to 46 cm in length (18 inches), giving the living animal an anticipated length of 3 metres (10 feet).

Very outstanding belemnite specimens have been found showing the potted soft parts of the animal. Some belemnites serve as index fossils, mainly in the Cretaceous Chalk Formation of Europe, enabling geologists to date the age the rocks in which they are found. Scientific Classification: Kingdom: Animalia Phylum: Mollusca Class: Cephalopoda Subclass: Coleoidea

Scientific Classification:

Kingdom: Animalia

Phylum: Mollusca

Class: Cephalopoda

Subclass: Coleoidea