Belemnites — a group of extinct cephalopods from the double-gill. The predators were likely to swim well; they had fins, large eyes, horny jaws, and an ink bag.
They had hooks on their tentacles. Inside the body was a massive carbonate rostrum similar to an arrowhead tip.The name of theе group of cephalopods is associated with these rostrums, which are often found in Mesozoic sediments.
Belemnites were very numerous in the Jurassic and Cretaceous periods. The oldest known finds of them belong to the beginning of the Jurassic (Schwegleria and a form close to Subhastites, Hettangian Age), and possibly to the late Triassic (family Sinobelemnitidae, Carnian Age). Some authors attributed to belemnites a number of forms from Сarboniferous and Permian periods, but later they were transferred to other groups.
The Belemnites probably died out on the border of the Cretaceous and Paleogene, but there were also suggestions that some Eocene forms (Bayanoteuthis, Styracoteuthis) belonged to them. The belemnites looked like squids, but, unlike them, they had a real inner shell consisting of three parts: a fragmocon, a proostracum, and a rostrum.
The most common fossilized remains of belemnites are found in marine Jurassic and Cretaceous sediments. The best preserved in the fossil state is the belemnite rostrum – the most strongest part of the inner shell. In exceptional cases, prints of the soft body of belemnites are found.