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Belemnites (or belemnoids) are an extinct group of marine cephalopod
Cephalopod

The cephalopods are the mollusc class Cephalopoda characterized by bilateral symmetry, a prominent head, and a modification of the mollusk foot, a muscular hydrostat, into the form of cephalopod arms or tentacles....
, very similar in many ways to the modern squid
Squid

Squid are marine cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, Symmetry #Bilateral_symmetry, a mantle , and cephalopod arms....
 and closely related to the modern cuttlefish
Cuttlefish

Cuttlefish are Marine animals of the order Sepiida belonging to the Cephalopoda class . Despite their common name, cuttlefish are not fish but molluscs....
. Like them, the belemnites possessed an ink sac
Ink sac

With the exception of nocturnal and very deep water cephalopods, all coeloids which dwell in light conditions have an ink sac, which can be used to expel a cloud of dark cephalopod ink to confuse predators....
, but, unlike the squid, they possessed ten arms of roughly equal length and no tentacles.

Belemnites were numerous during the Jurassic
Jurassic

The Jurassic is a geologic period that extends from about annum to  Ma, that is, from the end of the Triassic to the beginning of the Cretaceous....
 and Cretaceous
Cretaceous

The Cretaceous , usually abbreviated K for its German translation Kreide, is a geologic period from circa to million years ago . In the geologic timescale, the Cretaceous follows on the Jurassic period and is followed by the Paleogene period....
 periods, and their fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
s are abundant in Mesozoic
Mesozoic

The Mesozoic Era is one of three Geologic time scale of the Phanerozoic eon . The division of time into eras dates back to Giovanni Arduino, in the 18th century, although his original name for the era now called the 'Mesozoic' was 'Secondary' ....
 marine rocks, often accompanying their cousins the ammonite
Ammonite

Ammonites are an Extinction group of marine animals of the Subclass Ammonoidea in the class Cephalopoda, phylum Mollusca. They are excellent index fossils, and it is often possible to link the rock layer in which they are found to specific Geologic time scale....
s.






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Belemnites (or belemnoids) are an extinct group of marine cephalopod
Cephalopod

The cephalopods are the mollusc class Cephalopoda characterized by bilateral symmetry, a prominent head, and a modification of the mollusk foot, a muscular hydrostat, into the form of cephalopod arms or tentacles....
, very similar in many ways to the modern squid
Squid

Squid are marine cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, Symmetry #Bilateral_symmetry, a mantle , and cephalopod arms....
 and closely related to the modern cuttlefish
Cuttlefish

Cuttlefish are Marine animals of the order Sepiida belonging to the Cephalopoda class . Despite their common name, cuttlefish are not fish but molluscs....
. Like them, the belemnites possessed an ink sac
Ink sac

With the exception of nocturnal and very deep water cephalopods, all coeloids which dwell in light conditions have an ink sac, which can be used to expel a cloud of dark cephalopod ink to confuse predators....
, but, unlike the squid, they possessed ten arms of roughly equal length and no tentacles.

Belemnites were numerous during the Jurassic
Jurassic

The Jurassic is a geologic period that extends from about annum to  Ma, that is, from the end of the Triassic to the beginning of the Cretaceous....
 and Cretaceous
Cretaceous

The Cretaceous , usually abbreviated K for its German translation Kreide, is a geologic period from circa to million years ago . In the geologic timescale, the Cretaceous follows on the Jurassic period and is followed by the Paleogene period....
 periods, and their fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
s are abundant in Mesozoic
Mesozoic

The Mesozoic Era is one of three Geologic time scale of the Phanerozoic eon . The division of time into eras dates back to Giovanni Arduino, in the 18th century, although his original name for the era now called the 'Mesozoic' was 'Secondary' ....
 marine rocks, often accompanying their cousins the ammonite
Ammonite

Ammonites are an Extinction group of marine animals of the Subclass Ammonoidea in the class Cephalopoda, phylum Mollusca. They are excellent index fossils, and it is often possible to link the rock layer in which they are found to specific Geologic time scale....
s. The belemnites become extinct at the end of the Cretaceous period along with the ammonites. The belemnites' origin lies within the bactritoid
Bactritida

The Bactritida form a small order of more or less straight-shelled cephalopods that first appeared during the Emsian Stage of the Devonian Period and persisted until the Carnian Stage of the Triassic Period ....
 nautiloids, which date from the Devonian
Devonian

The Devonian is a geologic period of the Paleozoic era spanning from . It is named after Devon, England, where rocks from this period were first studied....
 period; well-formed belemnite guards can be found in rocks dating from the Mississippian (or Early Carboniferous
Carboniferous

The Carboniferous is a geologic period that extends from the end of the Devonian period, about 359.2 ? 2.5 annum , to the beginning of the Permian period, about 299.0 ? 0.8 Ma ...
) onward through the Cretaceous. Other fossil cephalopod
Cephalopod

The cephalopods are the mollusc class Cephalopoda characterized by bilateral symmetry, a prominent head, and a modification of the mollusk foot, a muscular hydrostat, into the form of cephalopod arms or tentacles....
s include baculite
Baculite

Baculites is a genus of Extinction marine animals in the phylum Mollusca and class Cephalopoda. They are a nearly straight-shelled type of heteromorph ammonite that lived worldwide throughout the Late Cretaceous period....
s, nautiloid
Nautiloid

Nautiloids are a group of marine mollusks in the subclass Nautiloidea, which all possess an external shell, the best-known example being the modern nautiluses....
s and goniatite
Goniatite

Goniatites are an extinction group of ammonite, which are shelled cephalopods related to squids, belemnites, octopuses, and cuttlefish, and more distantly to the nautiloids....
s.

Belemnit
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
Phragmocone

The phragmocone is the chambered portion of the Animal shell of a cephalopod. It is divided by Septa into camerae.In most nautiloids and Ammonoideas, the phragmocone is a long, straight, curved, or coiled structure, in which the camarae are linked by a siphuncle which determines buoyancy by means of gas exchange....
). 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 homologous with the shells of other cephalopods and are similarly composed of aragonite
Aragonite

Aragonite is a carbonate mineral, one of the two common, naturally occurring polymorphism of calcium carbonate, calciumcarbonoxygen3....
, belemnite guards are evolutionarily novel and are composed of calcite
Calcite

Calcite is a Carbonate minerals and the most stable Polymorphism of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite....
, thus tending to preserve well. Broken guards show a structure of radiating calcite fibers and may also display concentric growth rings. The bulk geochemical
Isotope geochemistry

Isotope geochemistry is an aspect of geology based upon study of the relative and absolute concentrations of the chemical element and their isotopes in the Earth....
 signature contained within belemnite guards of the Peedee Formation (Cretaceous
Cretaceous

The Cretaceous , usually abbreviated K for its German translation Kreide, is a geologic period from circa to million years ago . In the geologic timescale, the Cretaceous follows on the Jurassic period and is followed by the Paleogene period....
, southeast USA) has long been used as a global standard ("PDB") against which all other geochemical
Isotope geochemistry

Isotope geochemistry is an aspect of geology based upon study of the relative and absolute concentrations of the chemical element and their isotopes in the Earth....
 samples are measured, for both carbon isotopes
Isotopes of carbon

Carbon Standard atomic mass: 12.0107 unified atomic mass unit...
 and oxygen isotopes
Isotopes of oxygen

There are three stable isotopes of oxygen that lead to oxygen having a standard atomic mass of 15.9994 unified atomic mass unit. There are also 14 other isotopes that have unstable nuclei....
.

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 belemnite Megateuthis gigantea
Megateuthis gigantea

Megateuthis gigantea is the largest known belemnite species. The guard of M. gigantea, which has been found in Europe and Asia, can measure up to 46 centimetres in length , giving the living animal an estimated length of 3 metres ....
, which is found in Europe
Europe

Europe is, conventionally, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural , the Caspian Sea, and by the Caucasus Mountains to the southeast....
 and Asia
Asia

Asia is the world's largest and most populous continent. It covers 8.6% of the Earth's total surface area and, with over 4 billion people, it contains more than 60% of the world's current human population....
, can measure up to 46 cm in length (18 inches), giving the living animal an estimated length of 3 metres (10 feet).

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"
Orthoceras

Orthoceras is a genus of extinct nautiloid cephalopod. This genus is sometimes called Orthoceratites. Note it is sometimes misspelled as Orthocera, Orthocerus or Orthoceros ....
). It remains unclear whether these deposits represent post-mating mass death events as are common among modern cephalopods and other semelparous creatures.

Some belemnites (such as Belemnites) serve as index fossil
Index fossil

Index fossils are fossils used to define and identify geologic columns . They work on the premise that, although different sediments may look different depending on the conditions under which they were laid down, they may include the remains of the same species of fossil....
s, particularly in the Cretaceous Chalk Formation
Chalk Formation

The Chalk Group is a lithostratigraphy in the northwestern part of Europe. It is characterised by thick deposits of chalk, a soft porous white limestone, deposited in a marine environment during the Upper Cretaceous period ....
 of Europe, enabling geologist
Geologist

For other uses, see Geologist .A geologist is a contributor to the science of geology, studying the physical structure and processes of the Earth and planets of the solar system ....
s to date the age the rocks
Rock (geology)

In geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock....
 in which they are found.

Like some modern squid, belemnite arms carried a series of small hooks for grabbing prey. Belemnites were efficient carnivore
Carnivore

A carnivore , meaning 'meat eater' , is any animal with a diet consisting mainly of meat, whether it comes from animals living or dead .In a more general sense, an animal may be considered a carnivore if it prefers feeding on animal matter over plant matter....
s that caught small fish
Fish

A fish is any marine biology vertebrate animal that is typically ectothermic , covered with scale , and equipped with two sets of paired fins and several unpaired fins....
 and other marine animals with their arms and ate them with their beak-like jaws. In turn, belemnites appear to have formed part of the diet of marine reptile
Reptile

Reptiles, or members of the class Reptilia, are air-breathing, cold-blooded vertebrates that have skin covered in scale as opposed to hair or feathers....
s such as Ichthyosaur
Ichthyosaur

Ichthyosaurs were giant marine reptiles that resembled fish and dolphins. Ichthyosaurs thrived during much of the Mesozoic era; based on fossil evidence, they first appeared approximately 245 million years ago and disappeared about 90 million years ago, about 25 million years before the dinosaurs became extinct....
s, whose fossilized stomach
Stomach

In most mammals, the stomach is a hollow muscular organ of the gastrointestinal tract involved in the second phase of digestion, following mastication....
s frequently contain phosphatic
Phosphate minerals

Phosphate minerals are those minerals that contain the tetrahedrally coordinated phosphate anion along with the freely substituting arsenate and vanadate ....
 hooks from the arms of cephalopods.

Classification

Note: all families extinct
  • Cohort Belemnoidea
    • Basal
      Basal (phylogenetics)

      In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group form an outgroup to the rest of the clade, such as in the following example:...
       and unresolved
      • Genus Jeletzkya
    • Order Aulacocerida
      Aulacocerida

      Aulacocerida is an extinct order of belemnoids....
      • Family Aulacoceratidae
      • Family Dictyoconitidae
      • Family Hematitidae
      • Family Palaeobelemnopseidae
      • Family Xiphoteuthididae
    • Order Belemnitida
      • Suborder Belemnitina
        • Family Cylindroteuthididae
        • Family Hastitidae
        • Family Oxyteuthididae
        • Family Passaloteuthididae
        • Family Salpingoteuthididae
      • Suborder Belemnopseina
        • Family Belemnitellidae
        • Family Belemnopseidae
        • Family Dicoelitidae
        • Family Dimitobelidae
        • Family Duvaliidae
    • Order Belemnoteuthina
      • Family Belemnotheutididae
      • Family Chitinobelidae
      • Family Sueviteuthididae
    • Order Diplobelida
      • Family Chondroteuthididae
      • Family Diplobelidae
    • Order Phragmoteuthida
      • Family Phragmoteuthididae


See also

  • Nautiloidea
  • Ammonoidea


External links