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{{Automatic taxobox |
{{Automatic taxobox |
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| name = Belemnites |
| name = Belemnites |
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| fossil_range = [[ |
| fossil_range = [[Carnian]]–[[Maastrichtian]] <br>234–66 Ma<ref name="Iba2012">{{Cite journal | last1 = Iba | first1 = Y. | last2 = Sano | first2 = S. -I. | last3 = Mutterlose | first3 = J. | last4 = Kondo | first4 = Y. | title = Belemnites originated in the Triassic—A new look at an old group | doi = 10.1130/G33402.1 | journal = Geology | year = 2012 }}</ref> |
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| image = Passaloteuthis bisulcata.JPG |
| image = Passaloteuthis bisulcata.JPG |
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| image_caption=''[[Passaloteuthis|Passaloteuthis bisulcata]]'' |
| image_caption=''[[Passaloteuthis|Passaloteuthis bisulcata]]'' showing soft anatomy |
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| taxon =Belemnitida |
| taxon =Belemnitida |
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| authority = [[Karl Alfred Ritter von Zittel|Zittel]], 1895 |
| authority = [[Karl Alfred Ritter von Zittel|Zittel]], 1895 |
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[[Belemnotheutina]] |
[[Belemnotheutina]] |
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}} |
}} |
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'''Belemnitida''' (or '''belemnites''') is an [[extinct]] [[order (biology)|order]] of [[cephalopod]]s |
'''Belemnitida''' (or '''belemnites''') is an [[extinct]] [[order (biology)|order]] of [[squid]]-like [[cephalopod]]s that existed from the [[Late Triassic]] to [[Late Cretaceous]]. The belemnite is the [[state fossil]] of [[Delaware]]. |
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==Taxonomy== |
==Taxonomy== |
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===Evolution=== |
===Evolution=== |
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[[File:Opale3 (Australie).jpg|thumb|left|[[Opalized]] ''[[Peratobelus]]'' guard]] |
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Belemnites were traditionally thought to have evolved in northern Europe in the [[Hettangian]] stage of the [[Early Jurassic]]. However, Hettangian-age belemnites also have been found in Japan. There are some Chinese specimens that may date to the [[Carnian]] stage of the [[Late Triassic]], though it is possible these were merely deposited in a different [[stratum]] and actually date to the [[Middle Jurassic]]. Early belemnites were generally considered to be small, with the earliest European forms, ''[[Schwegleria]]'' and ''[[Subhastites]]'', having a cone diameters of {{cvt|4|and|10|mm}} respectively. However, a Japanese cone had a {{cvt|33|mm}} diameter.<ref name="Iba2012"/> |
Belemnites were traditionally thought to have evolved in northern Europe in the [[Hettangian]] stage of the [[Early Jurassic]]. However, Hettangian-age belemnites also have been found in Japan. There are some Chinese specimens that may date to the [[Carnian]] stage of the [[Late Triassic]], though it is possible these were merely deposited in a different [[stratum]] and actually date to the [[Middle Jurassic]]. Early belemnites were generally considered to be small, with the earliest European forms, ''[[Schwegleria]]'' and ''[[Subhastites]]'', having a cone diameters of {{cvt|4|and|10|mm}} respectively. However, a Japanese cone had a {{cvt|33|mm}} diameter.<ref name="Iba2012"/> |
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==Description== |
==Description== |
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[[File:BelemnitesJurassicWyoming.jpg|thumb|Fossil belemnite guards from the [[Jurassic]] of Wyoming]] |
[[File:BelemnitesJurassicWyoming.jpg|thumb|Fossil belemnite guards from the [[Jurassic]] of Wyoming]] |
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===Hard structures=== |
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The belemnite cone is composed of three parts: the initial pro-ostracum which is similar to the [[gladius (cephalopod)|gladius]] of squid, then the chambered [[phragmocone]], and finally the guard at the very tip. The space between the phragmocone and the rostrum is known as the alveolus. The cone, in life, would have been encased in muscle and [[connective tissue]]. They had [[calcite|calcitic]] guards,<ref name=klug/> and [[aragonite|aragonitic]] pro-ostracum and phragmocone.<ref name=monks/> The pro-ostracum served a similar function to the [[gladius (cephalopod)|gladius]] of squid. The phragmocone was divided into chambers, much like the shells of [[cuttlefish]] and [[nautilus]]es.<ref name=wani/> |
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The chambered phragmocone increased buoyancy by reducing density, and the denser guard served to counteract this, [[analogy (biology)|analogous]] to the [[camera (cephalopod)|camera]] of [[nautiloid]]s. However, the guard may have served to cut through waves while swimming at the surface, though modern cephalopods generally stay completely submerged. Though unlikely, it is possible fossilization increased the density of the guard, and it may have been up to 20% more porous in life. Fins may have been attached to the guard, or the guard may have lent support for large fins. Including arms, guards can account for one fifth to one third of the total length of a belemnite. Belemnites may have behaved much like modern [[ram's horn squid]], having the chambers of the phragmocone flooded and slowly releasing more seawater as the animal increases in size over its lifetime to maintain [[neutral buoyancy]].<ref name=monks>{{cite journal|first=N.|last=Monks|first2=D.|last2=Hardwick|first3=A. S.|last3=Gale|year=1996|title=The function of the belemnite guard|journal=Paläontologische Zeitschrift|volume=70|issue=3|pages=425–431|doi=10.1007/BF02988082|url=https://www.researchgate.net/publication/226471454}}</ref> |
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| ⚫ | At the tip of the phragmocone beneath the rostrum is a tiny, spherical or cup-like nodule known as the "protoconch," the remains of the [[embryo]]nic shell. At the forward part of the phragmocone is a thin, fragile structure known as the "proostracum". It is usually spoon-like in shape and extends over the dorsal part of the [[Mantle (mollusc)|mantle]].{{cn|date=January 2019}} |
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| ⚫ | |||
| ⚫ | At the tip of the phragmocone beneath the rostrum is a tiny, spherical or cup-like nodule known as the "[[protoconch]]," the remains of the [[embryo]]nic shell.<ref name=wani>{{cite journal|first=R.|last=Wani|first2=A.|last2=Tajiki|first3=K.|last3=Ikuno|first4=T.|last4=Iwasaki|year=2017|title=Ontogenetic trajectories of septal spacing in Early Jurassic belemnites from Germany and France, and their palaeobiological implications|journal=The Depositional Record|volume=61|issue=1|pages=77–88|doi=10.1111/pala.12327}}</ref> At the forward part of the phragmocone is a thin, fragile structure known as the "proostracum". It is usually spoon-like in shape and extends over the dorsal part of the [[Mantle (mollusc)|mantle]].{{cn|date=January 2019}} |
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===Soft anatomy=== |
===Soft anatomy=== |
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| ⚫ | Belemnites had a [[radula]]–the mouth–embedded in the [[buccal mass]]–the first part of a [[gastropod]] digestive system–similar to open ocean predatory cephalopods. The radula had rows of seven teeth, consistent with modern predatory squid. The [[statocyst]]s–which give a sense of [[equilibrioception|balance]] and function much like the [[cochlea]] of the ear–were large, much like in modern fast-moving squid.<ref name=klug>{{cite journal|last=Klug|first=C.|last2=Schweigert|first2=G.|last3=Fuchs|first3=D.|last4=Kruta|first4=I.|last5=Tischlinger|first5=H.|year=2016|title=Adaptations to squid-style high-speed swimming in Jurassic belemnitids|journal=Biology Letters|volume=12|issue=1|doi=10.1098/rsbl.2015.0877|pmid=26740564|pmc=4785926}}</ref> |
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| ⚫ | |||
| ⚫ | Belemnites had a [[radula]]–the mouth–embedded in the [[buccal mass]]–the first part of a [[gastropod]] digestive system–similar to open ocean predatory cephalopods. The radula had rows of seven teeth, consistent with modern predatory squid. The [[ |
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In cephalopods, water is siphoned into the [[mantle cavity]] and expelled for [[jet propulsion]] using the [[hyponome]]. Though the hyponome was well-developed in belemnites,<ref name=klug/> the phragmocone was large, implying a small mantle cavity and thus less jet propulsion efficiency. Like some modern squid, belemnites may have mainly used large fins to coast along currents.<ref name=monks/> Two ''[[Acanthoteuthis]]'' specimens with preserved soft anatomy elements had a pair of fins near the top of their guards which were rhomboid in shape; however, they had different sized fins, possibly owing to [[sexual dimorphism]], age, or distortion during fossilization. These adaptations indicate an approximate swimming speed of {{cvt|1.1|to|1.8|kph}} for belemnites.<ref name=klug/> |
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| ⚫ | These remains also indicate the presence of an [[ink sac]], hard beaks, and large eyes |
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[[File:Belemnotheutis 3d.jpg|thumb|upright|''[[Belemnotheutis]]'']] |
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| ⚫ | These remains also indicate the presence of an [[ink sac]], hard beaks, and large eyes. Well preserved specimens have even retained evidence of strong muscular fibers in the mantle, indicating that they were powerful swimmers like modern squid and unlike other cephalopods of their time such as [[Ammonoidea|ammonoids]] and cymatoceratid nautiloids.{{cn}} |
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Belemnites had [[chitin]]ous, tactile, hooked tentacles with suckers. The hooks were fish-hook shaped, though curvature varied species to species, and probably only the tip was exposed. The hooks were likely also chitinous. Most belemnites probably had ten tentacles, and the males, like in modern squid, probably had one or two [[hectocotyli]]–long, modified arms used in copulation. The hectocotyli feature a pair of enlarged hooks to latch onto the female at a safe distance to prevent getting stuck with one of her hooks. Like squid, the positioning of the large hooks could have been either at the tip or origin of the tentacle depending on the species. Copulation probably involved the male depositing [[spermatophore]] into the female's internal mantle chamber. The small hooks were used to catch prey, having two rows of hooks covering the entire breadth of the tentacle. A belemnite could have had between 100 and 800 hooks in total.<ref name=stevens/> |
Belemnites had [[chitin]]ous, tactile, hooked tentacles with suckers. The hooks were fish-hook shaped, though curvature varied species to species, and probably only the tip was exposed. The hooks were likely also chitinous. Most belemnites probably had ten tentacles, and the males, like in modern squid, probably had one or two [[hectocotyli]]–long, modified arms used in copulation. The hectocotyli feature a pair of enlarged hooks to latch onto the female at a safe distance to prevent getting stuck with one of her hooks. Like squid, the positioning of the large hooks could have been either at the tip or origin of the tentacle depending on the species. Copulation probably involved the male depositing [[spermatophore]] into the female's internal mantle chamber. The small hooks were used to catch prey, having two rows of hooks covering the entire breadth of the tentacle. A belemnite could have had between 100 and 800 hooks in total.<ref name=stevens/> |
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===Pathology=== |
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[[File:Gonioteuthis quadrata (Blainville, 1827) guard with a zigzag-like deformation - photo vs. MRI.png|left|upright|thumb|[[MRI]] of a deformed ''[[Gonioteuthis]]'' guard]] |
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Belemnite guards have sometimes been found with fractures with signs of healing. It has been interpreted in the past that these are evidence of digging, with belemnites using their guard to dig up prey on the seafloor; however, belemnites are now generally interpreted to have been open ocean predators. A deformed, zigzag-like guard of a ''[[Gonioteuthis]]'' was likely the result of a failed predation attempt. Two other ''Gonioteuthis'' guard specimens exhibit a double-pointed tip, probably stemming from some traumatic event. One belemnite guard also presents a double-pointed tip, with one points projecting higher than the other, probably a sign of an infection or settlement of a parasite. A ''[[Neoclavibelus]]'' guard features a large growth on the side likely stemming from a parasitic infection. A ''[[Hibolithes]]'' guard shows a large ovoid bubble near the base, likely deriving from a parasitic [[cyst]].<ref>{{cite journal|url=https://hal.archives-ouvertes.fr/hal-00297517/document|first=D.|last=Mietchen|first2=H.|last2=Keupp3|first3=B.|last3=Manz|first4=F.|last4=Volke|year=2005|title=Non-invasive diagnostics in fossils – Magnetic Resonance Imaging of pathological belemnites|journal=Biogeosciences|volume=2|pages=133–140|doi=10.5194/bg-2-133-2005}}</ref> |
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==Paleoecology== |
==Paleoecology== |
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Belemnites were likely an abundant and important food source to many sea-going creatures of the Mesozoic. Belemnite hook remains have been found in the stomach contents of [[crocodilia]]ns, [[plesiosaur]]s, and [[icthyosaur]]s; and the [[coprolite]] remains of icthyosaurs and the extinct [[thylacocephala]]n crustaceans. A {{cvt|1.6|m}} shark had around 250 belemnite radulas in its stomach.<ref name=stevens>{{cite journal|url=https://www.tandfonline.com/doi/pdf/10.1080/00288306.2010.526548|first=G. R.|last=Stevens|year=2010|title=Palaeobiological and morphological aspects of Jurassic ''Onychites'' (cephalopod hooks) and new records from the New Zealand Jurassic|journal=New Zealand Journal of Geology and Geophysics|volume=53|issue=4|pages=395–412|doi=10.1080/00288306.2010.526548}}</ref> |
Belemnites inhabited the [[nearshore]] and mid-[[continental shelf|shelf]] zones. They were likely an abundant and important food source to many sea-going creatures of the Mesozoic. Belemnite hook remains have been found in the stomach contents of [[crocodilia]]ns, [[plesiosaur]]s, and [[icthyosaur]]s; and the [[coprolite]] remains of icthyosaurs and the extinct [[thylacocephala]]n crustaceans. A {{cvt|1.6|m}} shark had around 250 belemnite radulas in its stomach.<ref name=stevens>{{cite journal|url=https://www.tandfonline.com/doi/pdf/10.1080/00288306.2010.526548|first=G. R.|last=Stevens|year=2010|title=Palaeobiological and morphological aspects of Jurassic ''Onychites'' (cephalopod hooks) and new records from the New Zealand Jurassic|journal=New Zealand Journal of Geology and Geophysics|volume=53|issue=4|pages=395–412|doi=10.1080/00288306.2010.526548}}</ref> |
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Belemnites had a great diversification over the course of 130 million years before becoming extinct in the [[Cretaceous–Paleogene extinction event]], around 66 mya. Squid, cuttlefish, and [[octopus]]es experienced a diversification by the [[Middle Jurassic]], and began to outcompete and eventually replace belemnites at the beginning of the [[Cretaceous]].<ref>{{cite journal|url=http://ibayasuhiro.com/Publications_files/Iba_et_al_2011_Geology.pdf|first=Y.|last=Iba|first2=J.|last2=Mutterlose|first3=K.|last3=Tanabe|first4=S.|last4=Sano|first5=A.|last5=Misaki|first6=K.|last6=Terabe|year=2011|title=Belemnite extinction and the origin of modern cephalopods 35 m.y. prior to the Cretaceous−Paleogene event|journal=Geological Society of America|volume=39|issue=5|pages=483–486|doi=:10.1130/G31724.1}}</ref><ref>{{cite journal|first=A. R.|last=Tanner|first2=D.|last2=Fuchs|first3=I. E.|last3=Winkelmann|first4=M.|last4=Thomas|first5=P.|last5=Gilbert|year=2017|title=Molecular clocks indicate turnover and diversification of modern coleoid cephalopods during the Mesozoic Marine Revolution|journal=Proceedings of the Royal Society B: Biological Sciences|volume=284|issue=1850|page=20162818|doi=10.1098/rspb.2016.2818|pmc=5360930|pmid=28250188}}</ref> |
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==See also== |
==See also== |
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==References== |
==References== |
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{{Commons category| |
{{Commons category|Belemnitida}} |
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{{Wikisourcehas|2=[[s:Philosophical Transactions/Volume 54/An Attempt to Account for the Origin and the Formation of the Extraneous Fossil commonly called the Belemnite|An Attempt to Account for the Origin and the Formation of the Extraneous Fossil commonly called the Belemnite]]}} |
{{Wikisourcehas|2=[[s:Philosophical Transactions/Volume 54/An Attempt to Account for the Origin and the Formation of the Extraneous Fossil commonly called the Belemnite|An Attempt to Account for the Origin and the Formation of the Extraneous Fossil commonly called the Belemnite]]}} |
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{{Reflist}} |
{{Reflist}} |
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Revision as of 19:36, 26 January 2019
| Belemnites | |
|---|---|
| |
| Passaloteuthis bisulcata showing soft anatomy | |
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Superorder: | †Belemnoidea |
| Order: | †Belemnitida Zittel, 1895 |
| Suborders | |
Belemnitida (or belemnites) is an extinct order of squid-like cephalopods that existed from the Late Triassic to Late Cretaceous. The belemnite is the state fossil of Delaware.
Taxonomy
Evolution
Belemnites were traditionally thought to have evolved in northern Europe in the Hettangian stage of the Early Jurassic. However, Hettangian-age belemnites also have been found in Japan. There are some Chinese specimens that may date to the Carnian stage of the Late Triassic, though it is possible these were merely deposited in a different stratum and actually date to the Middle Jurassic. Early belemnites were generally considered to be small, with the earliest European forms, Schwegleria and Subhastites, having a cone diameters of 4 and 10 mm (0.16 and 0.39 in) respectively. However, a Japanese cone had a 33 mm (1.3 in) diameter.[1]
In light of this, it is now thought that belemnites were common during the early Jurassic. It is more likely they evolved around 234 million years ago in the Carnian stage of the Late Triassic in a cephalopod radiation alongside the octopus-like Prototeuthina and the squid-like Phragmoteuthida. Considering belemnites likely were an important and abundant food source to marine reptiles and sharks, their early evolution probably contributed to the reconstruction of the marine ecosystem following the Triassic–Jurassic extinction event.[1]
Phylogeny
Belemnites are cephalopods. Before preserved soft body parts were discovered, it was unknown whether it belonged to the superorder Octopodiformes or Decapodiformes, but it is now thought to belong to the latter.[2]
| Cephalopoda |
Their preserved fossil guards are used to measure the ancient isotopic signature of the waters the individual inhabited in life, which gives information on the climate, habitat, and the carbon cycle.[2]
Description
Hard structures
The belemnite cone is composed of three parts: the initial pro-ostracum which is similar to the gladius of squid, then the chambered phragmocone, and finally the guard at the very tip. The space between the phragmocone and the rostrum is known as the alveolus. The cone, in life, would have been encased in muscle and connective tissue. They had calcitic guards,[2] and aragonitic pro-ostracum and phragmocone.[3] The pro-ostracum served a similar function to the gladius of squid. The phragmocone was divided into chambers, much like the shells of cuttlefish and nautiluses.[4]
The chambered phragmocone increased buoyancy by reducing density, and the denser guard served to counteract this, analogous to the camera of nautiloids. However, the guard may have served to cut through waves while swimming at the surface, though modern cephalopods generally stay completely submerged. Though unlikely, it is possible fossilization increased the density of the guard, and it may have been up to 20% more porous in life. Fins may have been attached to the guard, or the guard may have lent support for large fins. Including arms, guards can account for one fifth to one third of the total length of a belemnite. Belemnites may have behaved much like modern ram's horn squid, having the chambers of the phragmocone flooded and slowly releasing more seawater as the animal increases in size over its lifetime to maintain neutral buoyancy.[3]
At the tip of the phragmocone beneath the rostrum is a tiny, spherical or cup-like nodule known as the "protoconch," the remains of the embryonic shell.[4] At the forward part of the phragmocone is a thin, fragile structure known as the "proostracum". It is usually spoon-like in shape and extends over the dorsal part of the mantle.[citation needed]
Soft anatomy
Belemnites had a radula–the mouth–embedded in the buccal mass–the first part of a gastropod digestive system–similar to open ocean predatory cephalopods. The radula had rows of seven teeth, consistent with modern predatory squid. The statocysts–which give a sense of balance and function much like the cochlea of the ear–were large, much like in modern fast-moving squid.[2]
In cephalopods, water is siphoned into the mantle cavity and expelled for jet propulsion using the hyponome. Though the hyponome was well-developed in belemnites,[2] the phragmocone was large, implying a small mantle cavity and thus less jet propulsion efficiency. Like some modern squid, belemnites may have mainly used large fins to coast along currents.[3] Two Acanthoteuthis specimens with preserved soft anatomy elements had a pair of fins near the top of their guards which were rhomboid in shape; however, they had different sized fins, possibly owing to sexual dimorphism, age, or distortion during fossilization. These adaptations indicate an approximate swimming speed of 1.1 to 1.8 km/h (0.68 to 1.12 mph) for belemnites.[2]
These remains also indicate the presence of an ink sac, hard beaks, and large eyes. Well preserved specimens have even retained evidence of strong muscular fibers in the mantle, indicating that they were powerful swimmers like modern squid and unlike other cephalopods of their time such as ammonoids and cymatoceratid nautiloids.[citation needed]
Belemnites had chitinous, tactile, hooked tentacles with suckers. The hooks were fish-hook shaped, though curvature varied species to species, and probably only the tip was exposed. The hooks were likely also chitinous. Most belemnites probably had ten tentacles, and the males, like in modern squid, probably had one or two hectocotyli–long, modified arms used in copulation. The hectocotyli feature a pair of enlarged hooks to latch onto the female at a safe distance to prevent getting stuck with one of her hooks. Like squid, the positioning of the large hooks could have been either at the tip or origin of the tentacle depending on the species. Copulation probably involved the male depositing spermatophore into the female's internal mantle chamber. The small hooks were used to catch prey, having two rows of hooks covering the entire breadth of the tentacle. A belemnite could have had between 100 and 800 hooks in total.[5]
Pathology
Belemnite guards have sometimes been found with fractures with signs of healing. It has been interpreted in the past that these are evidence of digging, with belemnites using their guard to dig up prey on the seafloor; however, belemnites are now generally interpreted to have been open ocean predators. A deformed, zigzag-like guard of a Gonioteuthis was likely the result of a failed predation attempt. Two other Gonioteuthis guard specimens exhibit a double-pointed tip, probably stemming from some traumatic event. One belemnite guard also presents a double-pointed tip, with one points projecting higher than the other, probably a sign of an infection or settlement of a parasite. A Neoclavibelus guard features a large growth on the side likely stemming from a parasitic infection. A Hibolithes guard shows a large ovoid bubble near the base, likely deriving from a parasitic cyst.[6]
Paleoecology
Belemnites inhabited the nearshore and mid-shelf zones. They were likely an abundant and important food source to many sea-going creatures of the Mesozoic. Belemnite hook remains have been found in the stomach contents of crocodilians, plesiosaurs, and icthyosaurs; and the coprolite remains of icthyosaurs and the extinct thylacocephalan crustaceans. A 1.6 m (5 ft 3 in) shark had around 250 belemnite radulas in its stomach.[5]
Belemnites had a great diversification over the course of 130 million years before becoming extinct in the Cretaceous–Paleogene extinction event, around 66 mya. Squid, cuttlefish, and octopuses experienced a diversification by the Middle Jurassic, and began to outcompete and eventually replace belemnites at the beginning of the Cretaceous.[7][8]
See also
- Belemnoidea – Extinct group of squid-like animals
- Cuttlebone – Hard, brittle internal structure found in all members of the family Sepiidae
References
- ^ a b c Iba, Y.; Sano, S. -I.; Mutterlose, J.; Kondo, Y. (2012). "Belemnites originated in the Triassic—A new look at an old group". Geology. doi:10.1130/G33402.1.
- ^ a b c d e f Klug, C.; Schweigert, G.; Fuchs, D.; Kruta, I.; Tischlinger, H. (2016). "Adaptations to squid-style high-speed swimming in Jurassic belemnitids". Biology Letters. 12 (1). doi:10.1098/rsbl.2015.0877. PMC 4785926. PMID 26740564.
- ^ a b c Monks, N.; Hardwick, D.; Gale, A. S. (1996). "The function of the belemnite guard". Paläontologische Zeitschrift. 70 (3): 425–431. doi:10.1007/BF02988082.
- ^ a b Wani, R.; Tajiki, A.; Ikuno, K.; Iwasaki, T. (2017). "Ontogenetic trajectories of septal spacing in Early Jurassic belemnites from Germany and France, and their palaeobiological implications". The Depositional Record. 61 (1): 77–88. doi:10.1111/pala.12327.
- ^ a b Stevens, G. R. (2010). "Palaeobiological and morphological aspects of Jurassic Onychites (cephalopod hooks) and new records from the New Zealand Jurassic". New Zealand Journal of Geology and Geophysics. 53 (4): 395–412. doi:10.1080/00288306.2010.526548.
- ^ Mietchen, D.; Keupp3, H.; Manz, B.; Volke, F. (2005). "Non-invasive diagnostics in fossils – Magnetic Resonance Imaging of pathological belemnites". Biogeosciences. 2: 133–140. doi:10.5194/bg-2-133-2005.
{{cite journal}}: CS1 maint: numeric names: authors list (link) CS1 maint: unflagged free DOI (link) - ^ Iba, Y.; Mutterlose, J.; Tanabe, K.; Sano, S.; Misaki, A.; Terabe, K. (2011). "Belemnite extinction and the origin of modern cephalopods 35 m.y. prior to the Cretaceous−Paleogene event" (PDF). Geological Society of America. 39 (5): 483–486. doi::10.1130/G31724.1.
{{cite journal}}: Check|doi=value (help) - ^ Tanner, A. R.; Fuchs, D.; Winkelmann, I. E.; Thomas, M.; Gilbert, P. (2017). "Molecular clocks indicate turnover and diversification of modern coleoid cephalopods during the Mesozoic Marine Revolution". Proceedings of the Royal Society B: Biological Sciences. 284 (1850): 20162818. doi:10.1098/rspb.2016.2818. PMC 5360930. PMID 28250188.