{{Taxobox
| name = Belemnites
| fossil_range = Devonian-Cretaceous
| image = Belmnites.jpg
| image_width = 250px
| image_caption = Small Belemnite fossils
| regnum = Animalia
| phylum = Mollusca
| classis = Cephalopoda
| subclassis = Coleoidea
| unranked_ordo = Cohort †'''Belemnoidea'''
| subdivision_ranks = Extinct Orders
| subdivision = 
Aulacocerida<br>
Phragmoteuthida<br>
Belemnitida<br>
Diplobelida<br>
Belemnoteuthina
}}

'''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 them, the belemnites possessed an ink sac, but, unlike the squid, they possessed ten arms of roughly equal length and no tentacles.

Belemnites were numerous during 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.

left|thumb|A belemnite fossil from the [[Franconian Jura.]]

Normally with fossil belemnites only the back part of the shell (called the ''guard'' or ''rostrum'') is found. The guard is elongated and bullet-shaped, being cylindrical and either pointed or rounded 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''.

While belemnite phragmocones are geochemical signature contained within belemnite guards of the Peedee Formation (geochemical samples are measured, for both carbon isotopes and oxygen isotopes.

The guard, phragmocone and pro-ostracum were all internal to the living creature, forming a skeleton which was enclosed entirely by soft muscular tissue. The original living creature 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 creature, with the phragmocone behind the head and the pointed end of the guard facing backward. 
thumb|left|Belemnites 
The guard of the belemnite ''Megateuthis gigantea'', 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).

thumb|right|Belemnite fossils at [[Bristol City Museum and Art Gallery|Bristol City Museum, Bristol, England. Found in the Lower Lias strata, Gloucestershire, England.]]

Very exceptional belemnite specimens have been found showing the preserved soft parts of the animal.  Elsewhere in the fossil record, bullet-shaped belemnite guards are locally found in such profusion that such deposits are referred to semi-formally as "belemnite battlefields" (cf. "orthocone orgies").  It remains unclear whether these deposits represent post-mating mass death events as are common among modern cephalopods and other semelparous creatures.

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|nome=Belemniti
|statocons=fossile
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|superphylum=
|phylum=Mollusca
|subphylum=
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|superclasse=
|classe=Cephalopoda
|sottoclasse=	Coleoidea
|infraclasse=
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|ordine='''Belemnoidea'''
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Le '''Belemniti''' sono fossili comparsi nel estinti nel Cretacico (135-65 milioni di anni fa).

Erano cefalopodi marini, lontani parenti di polpi, seppie e calamari, caratterizzati da una fossilizzata.</br>
Nella conchiglia si distinguono 3 parti: il ''pro-ostraco'' (lamina cornea coperta di aragonite e raramente conservata), si prolunga dorsalmente nel ''fragmocono'' (a cono appuntito, arcuato e composto di aragonite) che s' inserisce nel ''rostro'' (cilindro-conico, molto robusto e costituito di calcite), che si fossilizza più facilmente.
Questo genere ha un rostro cilindrico di 5-10 cm., con un solco profondo per tutta la lunghezza.
Le belemniti, carnivore, forse simili al calamaro, si nutrivano di crostacei e pesci e forse vivevano in gruppo.