Belemnoids are an extinct group of marine
cephalopod
A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...
, very similar in many ways to the modern
squid
True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...
and closely related to the modern
cuttlefish
Cuttlefish or cuttles are marine molluscs of the order Sepiida. They belong to the class Cephalopoda which also includes squid, octopuses, and nautiluses. Cuttlefish have a unique internal shell, the cuttlebone, which is used for control of ...
. Like them, the belemnoids possessed an
ink sac
An ink sac is an anatomical feature that is found in many cephalopod mollusks used to produce the defensive cephalopod ink. With the exception of nocturnal and very deep water cephalopods, all Coleoidea (squid, octopus and cuttlefish) which dwell ...
, but, unlike the squid, they possessed ten
arms
Arms or ARMS may refer to:
*Arm or arms, the upper limbs of the body
Arm, Arms, or ARMS may also refer to:
People
* Ida A. T. Arms (1856–1931), American missionary-educator, temperance leader
Coat of arms or weapons
*Armaments or weapons
**Fi ...
of roughly equal length, and no
tentacle
In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...
s. The name "belemnoid" comes from the Greek word βέλεμνον, ''belemnon'' meaning "a dart or arrow" and the Greek word είδος, ''eidos'' meaning "form".
Belemnoids include belemnites (which belong to
order
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...
Belemnitida
Belemnitida (or the belemnite) is an extinct order of squid-like cephalopods that existed from the Late Triassic to Late Cretaceous. Unlike squid, belemnites had an internal skeleton that made up the cone. The parts are, from the arms-most to ...
proper), aulacocerids (order
Aulacocerida
Aulacocerida is an order of primitive coleoid cephalopods, possibly derived from michelinoceraitids ( Orthocerida) early in the Devonian, which in turn gave rise to the Belemnites.
Aulococerids are characterized by a straight, slim, conical sh ...
), phragmoteuthids (order
Phragmoteuthida
Phragmoteuthida is an order of extinct coleoid cephalopod
A cephalopod is any member of the molluscan class Cephalopoda ( Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals ar ...
), and diplobelids (order
Diplobelida).
Occurrence
Belemnoids were numerous during the
Jurassic
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
and
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
periods, and their
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
s are abundant in
Mesozoic
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...
marine rocks, often accompanying their cousins the
ammonite
Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...
s. The belemnoids become extinct at the end of the Cretaceous period along with the ammonites. The belemnoids' origin lies within the
bactritoid nautiloids, which date from the
Devonian
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...
period; well-formed belemnoid guards can be found in rocks dating from the
Mississippian (or Early
Carboniferous
The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...
) onward through the Cretaceous. Other fossil
cephalopod
A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...
s include
baculite
''Baculites'' ("walking stick rock") is an extinct genus of cephalopods with a nearly straight shell, included in the heteromorph ammonites. The genus, which lived worldwide throughout most of the Late Cretaceous, and which briefly survived the ...
s,
nautiloid
Nautiloids are a group of marine cephalopods ( Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and speciose, with over 2,500 recorded species ...
s and
goniatite
Goniatids, informally goniatites, are ammonoid cephalopods that form the order Goniatitida, derived from the more primitive Agoniatitida during the Middle Devonian some 390 million years ago (around Eifelian stage). Goniatites (goniatitids) survi ...
s.
Anatomy
Belemnoids possessed a central
phragmocone
The phragmocone is the chambered portion of the shell of a cephalopod. It is divided by septa into camerae.
In most nautiloids and ammonoids, the phragmocone is a long, straight, curved, or coiled structure, in which the camarae are linked by a ...
made of
aragonite
Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including prec ...
and with negative buoyancy.
To the rear of the creature was a heavy
calcite
Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
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.
[ The guard would account for between a third and a fifth of the length of the complete organism, arms included.][
Like some modern squid, belemnoid arms carried a series of small hooks for grabbing ]prey
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
. Belemnoids were efficient carnivore
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...
s that caught small fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
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
Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...
s such as Ichthyosaur
Ichthyosaurs (Ancient Greek for "fish lizard" – and ) are large extinct marine reptiles. Ichthyosaurs belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' – a designation introduced by Sir Richard Owen in 1842, altho ...
s, whose fossilized stomach
The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...
s frequently contain phosphatic hooks from the arms of cephalopods.
Ecology
Belemnoids were effectively neutrally buoyant, and swam in near-shore to mid-shelf oceans.[ 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.][
]
Preservation
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 the chambered portion of the shell of a cephalopod. It is divided by septa into camerae.
In most nautiloids and ammonoids, the phragmocone is a long, straight, curved, or coiled structure, in which the camarae are linked by a ...
''). 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 homologous with the shells of other cephalopods
A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, an ...
and are similarly composed of aragonite
Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including prec ...
, belemnoid guards are evolutionarily novel and are composed of calcite
Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
or aragonite
Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including prec ...
, thus tending to preserve well. Broken guards show a structure of radiating calcite fibers and may also display concentric growth rings
Dendrochronology (or tree-ring dating) is the scientific method of dating tree rings (also called growth rings) to the exact year they were formed. As well as dating them, this can give data for dendroclimatology, the study of climate and atmos ...
.
Diagenetic modifications of the shells are complex. Radiating calcitic crystals are thin, or very large, with a shape indicative of a strong alteration. In other samples, the aragonite - calcite boundary is not dependent on growth lines. 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
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
and Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...
, can measure up to in length, giving the living animal an estimated length of .
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. "orthocone orgies"). It remains unclear whether these deposits represent post-mating mass death events, as are common among modern cephalopods
A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, an ...
and other semelparous
Semelparity and iteroparity are two contrasting reproductive strategies available to living organisms. A species is considered semelparous if it is characterized by a single reproductive episode before death, and iteroparous if it is characteri ...
creatures.
Thunderstones
The name "thunderbolt
A thunderbolt or lightning bolt is a symbolic representation of lightning when accompanied by a loud thunderclap. In Indo-European mythology, the thunderbolt was identified with the 'Sky Father'; this association is also found in later Hell ...
" 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.[
]
Uses
The stable isotope
The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isotopes of the same element. The relative abundanc ...
composition of a belemnoid rostrum from the Peedee Formation
The Peedee Formation is a geologic formation in North and South Carolina. A marine deposit, named for exposures along the Great Peedee River, it preserves belemnites and foraminifera fossils dating from the Late Cretaceous. The formation is nota ...
(Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
, southeast USA) has long been used as a global standard (Peedee Belemnite, "PDB") against which other isotope geochemistry
Isotope geochemistry is an aspect of geology based upon the study of natural variations in the relative abundances of isotopes of various elements. Variations in isotopic abundance are measured by isotope ratio mass spectrometry, and can reveal ...
samples are measured, for both carbon isotopes
Carbon (6C) has 15 known isotopes, from to , of which and are stable. The longest-lived radioisotope is , with a half-life of years. This is also the only carbon radioisotope found in nature—trace quantities are formed cosmogenically by t ...
and oxygen isotopes
There are three known stable isotopes of oxygen (8O): Oxygen-16, , Oxygen-17, , and Oxygen-18, .
Radioactive isotope, Radioactive isotopes ranging from to have also been characterized, all short-lived. The longest-lived radioisotope is with a ...
.
Some belemnoids (such as ''Belemnites'' of Belemnitida
Belemnitida (or the belemnite) is an extinct order of squid-like cephalopods that existed from the Late Triassic to Late Cretaceous. Unlike squid, belemnites had an internal skeleton that made up the cone. The parts are, from the arms-most to ...
) serve as index fossil
Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock Stratum, strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictiona ...
s, particularly in the Cretaceous Chalk Formation
The Chalk Group (often just called the Chalk) is the lithostratigraphic unit (a certain number of rock strata) which contains the Upper Cretaceous limestone succession in southern and eastern England. The same or similar rock sequences occur acro ...
of Europe, enabling geologist
A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althou ...
s to date the age the rocks
In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its chemical composition, and the way in which it is formed. Rocks form the Earth's ...
in which they are found.
Classification
Note: all families extinct
*Clade Belemnoidea
** Basal and unresolved
*** Genus ''Jeletzkya
''Jeletzkya douglassae'' is a fossil coleoid from the early Pennsylvanian Mazon Creek lagerstätten and represents the earliest known crown-group squid. Non-mineralized anatomy is preserved and comprises ten hooked tentacles
In zoology, a ...
''
*** Genus '' Belemnotheutis''
** Order Aulacocerida
Aulacocerida is an order of primitive coleoid cephalopods, possibly derived from michelinoceraitids ( Orthocerida) early in the Devonian, which in turn gave rise to the Belemnites.
Aulococerids are characterized by a straight, slim, conical sh ...
*** Family Aulacoceratidae
*** Family Dictyoconitidae
*** Family Hematitidae
*** Family Palaeobelemnopseidae
*** Family Xiphoteuthidae
** Order Belemnitida
Belemnitida (or the belemnite) is an extinct order of squid-like cephalopods that existed from the Late Triassic to Late Cretaceous. Unlike squid, belemnites had an internal skeleton that made up the cone. The parts are, from the arms-most to ...
*** Suborder Belemnitina
Belemnitina is a suborder of belemnites, an extinct group of cephalopods. They have been identified as the oldest of all the belemnites and are likely the stockgroup for them. They were extant from the early Jurassic to the early Cretaceous. The ...
**** 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
Phragmoteuthida is an order of extinct coleoid cephalopod
A cephalopod is any member of the molluscan class Cephalopoda ( Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals ar ...
*** Family Phragmoteuthidae
*** Family Rhiphaeoteuthidae
See also
* Nautiloidea
Nautiloids are a group of marine cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and speciose, with over 2,500 recorded species. ...
* Ammonoidea
Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttle ...
* List of belemnites
This list of belemnite genera is an attempt to create a comprehensive listing of all genera that have ever been included in the extinct subclass Belemnoidea, excluding purely vernacular terms. The list includes all commonly accepted genera, as we ...
References
External links
TONMO.com Cephalopod Fossils articles and discussion forums
{{Taxonbar, from=Q14900832
Mesozoic cephalopods
Paleozoic cephalopods
Cephalopods by classification
Cretaceous cephalopods
Carboniferous cephalopods
Devonian cephalopods
Permian cephalopods
Jurassic cephalopods
Triassic cephalopods
Devonian first appearances
Maastrichtian extinctions