Editing Belemnoidea (section)

==Preservation==
[[File:Fossil-Belemnoidea-complete.jpg|thumb|left|A belemnoid fossil with preserved guard, [[mantle (mollusc)|mantle]] remnants, and arm hooks]]
[[File:Hibolites barnacle borings.JPG|thumb|left|Guard of ''[[Hibolites|Hibolites hastatus]]'' from the Jurassic near Moneva Teruel, Spain. The barnacle borings (''[[Rogerella]]'') show that it spent considerable time on the seafloor after death.]]

Normally with fossil belemnoids only the back part of the shell (called the ''guard'' or ''rostrum'') is found. The guard is usually elongated and bullet-shaped (though in some subgroups the rostrum may only exist as a thin layer coating the phragmocone). 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 belemnoid phragmocones are [[Homology (biology)|homologous]] with the shells of other [[cephalopods]] and are similarly composed of [[aragonite]], belemnoid guards are evolutionarily novel and are composed of [[calcite]] or [[aragonite]], thus tending to preserve well. Broken guards show a structure of radiating calcite fibers and may also display concentric [[growth rings]].

Diagenetic modifications of the shells are complex.<ref>{{Cite journal|last=Dauphin|first=Y.|date=1988|title=Diagenèse aragonite-calcite chez les Céphalopodes Coleoides : exemples des rostres d'Aulacoceras (Trias de Turquie) et Belopterina (Eocène de France)|journal=Bull. Mus. Natn. Hist. Nat. Paris|volume=4è série, 10 C|pages=107–135}}</ref><ref>{{Cite journal|last=Dauphin Y., Williams C.T. Barskov I.S.|date=2007|title=Aragonitic rostra of the Turonian belemnitid Goniocamax: arguments from diagenesis|journal=Acta Palaeontol. Pol.|volume=52|pages=85–97}}</ref> Radiating calcitic crystals are thin, or very large, with a shape indicative of a strong alteration.<ref>{{Cite journal|last=Dauphin|first=Y.|date=1984|title=Etude de la variabilite microstructurale des rostres de belemnites a partir de specimens provenant d'un sondage D.S.D.P. (leg 36 site 330) de l'Atlantique sud|journal=Revue de Paléobiologie|volume=3|pages=191–203}}</ref><ref>{{Cite journal|last=Dauphin|first=Y.|date=1988|title=Microstructure versus mineralogical and chemical data to estimate the state of preservation of fossil shells : a belemnitid example (Cephalopoda - Coleoidea)|journal=Revue de Paléobiologie|volume=7|pages=1–10}}</ref> In other samples, the aragonite - calcite boundary is not dependent on growth lines.<ref>{{Cite journal|last1=Barskov I.S.|first1=Kiyashko S.I.|last2=Dauphin Y.|first2=Denis A.|date=1997|title=Microstructures des zones calcitiques et aragonitiques des rostres de Goniocamax (Cephalopoda, Belemnitida) du Turonien de Sibérie du Nord|journal=Geodiversitas|volume=19|pages=669–680}}</ref> In a given fossil sites, some specimens are calcite, others are aragonite.

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.

The guard of the belemnoid ''[[Megateuthis gigantea]]'', which is found in [[Europe]] and [[Asia]], can measure up to {{convert|46|cm}} in length, giving the living animal an estimated length of {{convert|3|m|ft|0}}.

Very exceptional belemnoid 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. [[orthoceras|"orthocone orgies"]]). It remains unclear whether these deposits represent post-mating mass death events, as are common among modern [[cephalopods]] and other [[semelparous]] creatures.

===Thunderstones===
The name "[[thunderbolt]]" or "thunderstone" has also been traditionally applied to the fossilised rostra of belemnoids. The origin of these bullet-shaped stones was not understood, and thus a mythological explanation of stones created where lightning struck has arisen.<ref>
{{cite web|url= http://www.ucmp.berkeley.edu/taxa/inverts/mollusca/cephalopoda.php |title= The Cephalopoda: Squids, octopuses, nautilus, and ammonites |last= Vendetti |first= Jan |year= 2006 |publisher= UC Berkeley |access-date= 2013-06-07}}</ref>