Editing Belemnoidea

{{Short description|Extinct group of squid-like animals}}
{{Automatic taxobox
| name = Belemnoids
| fossil_range = {{fossil range|Devonian|Cretaceous}}
| image = Phragmoteuthis conocauda.JPG
| image_caption = Well preserved diplobelid ''[[Clarkeiteuthis|Clarkeiteuthis conocauda]]'', showing arm hooks and outline of mantle
| taxon = Belemnoidea
| authority = 
| subdivision_ranks = Orders
| subdivision = [[Aulacocerida]]<br />
[[Phragmoteuthida]]<br />
[[Belemnitida]]<br />
[[Diplobelida]]
}}
[[Image:BelemniteDB2.jpg|thumb|right|[[Paleoart|Artist's reconstruction]] of belemnoids.]]

'''Belemnoids''' are an extinct group of marine [[cephalopod]], very similar in many ways to the modern [[squid]]. Like them, the belemnoids possessed an [[ink sac]],<ref>Lehmann, U. 1981. ''The Ammonites: Their life and their world''. London: Cambridge University Press.</ref> but, unlike the squid, they possessed ten [[Cephalopod arm|arms]] of roughly equal length, and no [[tentacle]]s.<ref>{{Cite journal| first1 = P.| first2 = E. V.| title = The Jurassic Belemnite Suborder Belemnotheutina| journal = Palaeontology| volume = 47| issue = 4| last1 = Doyle| pages = 983–998| year = 2004| doi = 10.1111/j.0031-0239.2004.00395.x| last2 =    Shakides| doi-access = | bibcode = 2004Palgy..47..983D| s2cid = 129794707}}</ref>  The name "belemnoid" comes from the Greek word βέλεμνον, ''belemnon'' meaning "a dart or arrow" and the Greek word είδος, ''eidos'' meaning "form".<ref>''Webster's New Universal Unabridged Dictionary.'' 2nd ed. 1979.</ref>

Belemnoids include [[Belemnitida|belemnites]] (which belong to the [[Order (biology)|order]] [[Belemnitida]]), aulacocerids (order [[Aulacocerida]]), phragmoteuthids (order [[Phragmoteuthida]]), and diplobelids (order [[Diplobelida]]). Belemnoidea has been suggested to be paraphyletic by some authors.<ref>{{Cite journal |last1=Fuchs |first1=Dirk |last2=Iba |first2=Yasuhiro |last3=Tischlinger |first3=Helmut |last4=Keupp |first4=Helmut |last5=Klug |first5=Christian |date=October 2016 |title=The locomotion system of Mesozoic Coleoidea (Cephalopoda) and its phylogenetic significance |url=https://www.idunn.no/doi/10.1111/let.12155 |journal=Lethaia |language=en |volume=49 |issue=4 |pages=433–454 |doi=10.1111/let.12155 |bibcode=2016Letha..49..433F |issn=0024-1164|url-access=subscription }}</ref>

==Occurrence==
Belemnoids were numerous during the [[Jurassic]] and [[Cretaceous]] periods, and their [[fossil]]s are abundant in [[Mesozoic]] marine rocks, often accompanying their cousins the [[ammonite]]s. The belemnoids become extinct at the end of the Cretaceous period along with the ammonites. The belemnoids' origin lies within the [[Bactritida|bactritoid]] nautiloids, which date from the [[Devonian]] period; well-formed belemnoid guards can be found in rocks dating from the [[Mississippian age|Mississippian]] (or Early [[Carboniferous]]) onward through the Cretaceous. Other fossil [[cephalopod]]s include [[baculite]]s, [[nautiloid]]s and [[goniatite]]s.

==Anatomy==
Belemnoids possessed a central rostrom/guard made of [[aragonite]] and with negative buoyancy.<ref name=Monks1996>{{cite journal|year= 1996|title= The function of the belemnite guard | first3= A. S.|last3= Gale|journal=Paläontologische Zeitschrift | first2= J. D.|pages=425–431|last1= Monks|last2= Hardwick|doi= 10.1007/BF02988082|issue= 3–4|volume= 70|first1= H. J. D.|bibcode= 1996PalZ...70..425M |s2cid= 129722176 }}</ref>  To the rear of the creature was a heavy [[calcite]] guard whose main role appears to have been to counterbalance the front (towards the head) of the organism; it positions the centre of mass below the centre of buoyancy, increasing the stability of the swimming organism.<ref name=Monks1996/>  The guard would account for between a third and a fifth of the length of the complete organism, arms included.<ref name=Monks1996/>

Like some modern squid, belemnoid arms carried a series of small hooks for grabbing [[prey]]. Belemnoids were efficient [[carnivore]]s that caught small [[fish]] and other marine animals with their arms and ate them with their [[cephalopod beak|beak-like jaws]]. In turn, belemnites appear to have formed part of the diet of marine [[reptile]]s such as [[Ichthyosaur]]s, whose fossilized [[stomach]]s frequently contain [[Phosphate mineral|phosphatic]] hooks from the arms of cephalopods.

==Ecology==
Belemnoids were effectively neutrally buoyant, and swam in near-shore to mid-shelf oceans.<ref name=Monks1996/>  Their fins could be used to their advantage in all water speeds; in a gentle current they could be flapped for propulsion; in a stronger current they could be held erect to generate lift; and when swimming rapidly by jet propulsion they could be tucked in to the body for streamlining.<ref name=Monks1996/>

==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>

==Uses==
The [[isotope geochemistry|stable isotope]] composition of a belemnoid rostrum from the [[Peedee Formation]] ([[Cretaceous]], southeast USA) has long been used as a global standard (Peedee Belemnite, "PDB") against which other [[isotope geochemistry]] samples are measured, for both [[isotopes of carbon|carbon isotopes]] and [[isotopes of oxygen|oxygen isotopes]].

Some belemnoids (such as ''Belemnites'' of [[Belemnitida]]) serve as [[index fossil]]s, particularly in the Cretaceous [[Chalk Formation]] of Europe, enabling [[geologist]]s to date the age the [[rock (geology)|rocks]] in which they are found.

== Classification ==
<small>Note: all families extinct</small>
[[File:Hard parts of the Phragmoteuthida, Belemnitida and Diplobelida.png|thumb|Comparation of hard parts of Phragmoteuthida, Belemnitida and Diplobelida.]]
[[Image:ZoharBelemnite.JPG|thumb|Belemnoid from the very top bedding plane of the [[Zohar Formation]] (Jurassic) near [[Neve Atif]], the [[Golan]]. The central fold along the axis is characteristic of some genera.]]
[[File:Peratobelus sp., LW UVL.jpg|thumb|[[Opal]]ized belemnite rostrum under [[ultraviolet|UV]] illumination, from Cairn Hill mine, [[Coober Pedy]], [[South Australia]]]]
[[File:Hybodus with belemnites.JPG|thumb|Fossil of ''[[Hybodus]]'', with belemnites in the stomach region]]

*'''Clade Belemnoidea'''
** [[Basal (phylogenetics)|Basal]] and unresolved
*** Genus ''[[Jeletzkya]]''<!-- Palaeontology43(5): 919-926 -->
*** Genus ''[[Belemnotheutis]]''
** Order [[Aulacocerida]]
*** Family [[Aulacoceratidae]]
*** Family [[Dictyoconitidae]]
*** Family [[Hematitidae]]
*** Family [[Palaeobelemnopseidae]]
*** Family [[Xiphoteuthidae]]
** Order [[Belemnitida]]
*** Suborder [[Belemnitina]]
**** Family [[Cylindroteuthidae]]
**** Family [[Hastitidae]]
**** Family [[Oxyteuthidae]]
**** Family [[Passaloteuthidae]]
**** Family [[Salpingoteuthidae]]
*** Suborder [[Belemnopseina]]
**** Family [[Belemnitellidae]]
**** Family [[Belemnopseidae]]
**** Family [[Dicoelitidae]]
**** Family [[Dimitobelidae]]
**** Family [[Duvaliidae]]
*** Suborder [[Belemnotheutina]]
**** Family [[Belemnotheutidae]]
**** Family [[Chitinobelidae]]
**** Family [[Sueviteuthidae]]
** Order [[Diplobelida]]
*** Family [[Chondroteuthidae]]
*** Family [[Diplobelidae]]
** Order [[Phragmoteuthida]]
*** Family [[Phragmoteuthidae]]
*** Family [[Rhiphaeoteuthidae]]

== See also ==
* [[Nautiloidea]]
* [[Ammonoidea]]
* [[List of belemnites]]
{{Clear}}

==References==
{{Reflist}}

==External links==
{{Commons category|Belemnoidea}}
*[http://www.tonmo.com/science/fossils/fossilsjump.php TONMO.com Cephalopod Fossils articles and discussion forums]

{{Fossil cephalopods}}
{{Taxonbar|from=Q14900832}}

[[Category:Belemnoidea| ]]
[[Category:Mesozoic cephalopods]]
[[Category:Paleozoic cephalopods]]
[[Category:Cephalopods by classification]]
[[Category:Cretaceous cephalopods]]
[[Category:Carboniferous cephalopods]]
[[Category:Devonian cephalopods]]
[[Category:Permian cephalopods]]
[[Category:Jurassic cephalopods]]
[[Category:Triassic cephalopods]]
[[Category:Devonian first appearances]]
[[Category:Maastrichtian extinctions]]