Belemnites - (pronounced 'BEL-EM-NIGHT')

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

 

 

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

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

Normally 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 rounded 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 part of the shell (called the phragmocone). The phragmocone is usually 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 internal to the belemnite, forming a skeleton which was enclosed entirely by soft muscular tissue. The belemnite would have been larger than the fossilized shell, with a long streamlined body and prominent eyes. The guard would have been in place toward the rear of the belemnite, with the phragmocone behind the head and the pointed end of the guard facing backward.

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

Very exceptional belemnite specimens have been found showing the preserved soft parts of the animal. Some belemnites serve as index fossils, particularly 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

Extinct Orders:
Aulacocerida
Phragmoteuthida
Belemnitida
Diplobelida
Belemnoteuthina