Search Results - Belemnoidea

Belemnites were numerous during the Jurassic and Cretaceous periods, and their fossils are abundant in Mesozoic marine rocks, often accompanying their cousins the ammonites. The belemnites become extinct at the end of the Cretaceous period along with the ammonites. The belemnites' origin lies within the bactritoid nautiloids, which date from the Devonian period; well-formed belemnite guards can be found in rocks dating from the Mississippian (or Early Carboniferous) onward through the Cretaceous. Other fossil cephalopods include baculites, nautiloids and goniatites.

Belemnites comprise a central phragmocone, made of aragonite and with negative buoyancy.^[4] To the rear of the creature is a heavy calcite guard, whose main role appears to have been to counterbalance the front of the organism; it positions the centre of mass below the centre of buoyancy, increasing the stability of the swimming organism.^[4] The guard would account for between a third and a fifth of the length of the complete organism, arms included.^[4]

Like some modern squid, 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 phosphatic hooks from the arms of cephalopods.