Belemnitida

This is a good article. Click here for more information.
Source: Wikipedia, the free encyclopedia.
"Belemnite" redirects here. For the genus, see Belemnites (genus).

Belemnites
Temporal range:
Ma
[1]
The Early Jurassic Passaloteuthis bisulcata showing soft anatomy
Scientific classification Edit this 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. Unlike squid, belemnites had an internal skeleton that made up the cone. The parts are, from the arms-most to the tip: the tongue-shaped pro-ostracum, the conical phragmocone, and the pointy guard. The calcitic guard is the most common belemnite remain. Belemnites, in life, are thought to have had 10 hooked arms and a pair of fins on the guard. The chitinous
hooks were usually no bigger than 5 mm (0.20 in), though a belemnite could have had between 100 and 800 hooks in total, using them to stab and hold onto prey.

Belemnites were an important food source for many Mesozoic marine creatures, both the adults and the planktonic juveniles and they likely played an important role in restructuring marine ecosystems after the

open ocean, whereas others resided in the calmer littoral zone (nearshore) and fed off the seafloor. The largest belemnite known, Megateuthis elliptica
, had guards of 60 to 70 cm (24 to 28 in).

Belemnites were coleoids, a group that includes squid and octopuses, and are often grouped into the superorder Belemnoidea, though the higher classification of cephalopods is volatile and there is no clear consensus on how belemnites are related to modern coleoids. Guards can give information on the climate, habitat, and carbon cycle of the ancient waters they inhabited. Guards have been found since antiquity and have become part of folklore.[2][3]

Description

Shell

Cone diagram:
   r pro-ostracum,
   a alveolus,
   p phragmocone,
   g guard

The belemnite cone is composed of three parts. Going from arms to tip, these are the tongue-shaped pro-ostracum; the conical, chambered phragmocone; and the spear-shaped guard at the very tip.[4][5] The guard is attached to the phragmocone in a socket called the alveolus.[5][6] The cone, in life, would have been encased in muscle and connective tissue. They had calcite guards,[7] and aragonite pro-ostraca and phragmocones,[4] though a few belemnites also had aragonite guards,[8] and the alveolar side of the guards of belemnitellids may have also been of aragonite.[6] The pro-ostracum probably supported the soft parts of the belemnite, similar to the gladius of squid, and completely surrounded the phragmocone.[5][9]

The phragmocone was divided by

ram's horn squid, having the chambers of the phragmocone flooded and slowly releasing more seawater via the siphuncle tube as the animal increases in size and weight over its lifetime to maintain neutral buoyancy.[4] At the tip of the phragmocone beneath the guard is a tiny, cup-like protoconch, the remains of the embryonic shell.[1][9]

The dense guard probably served to

analogous to the camera of nautiloids. This would have allowed the animal to move horizontally through the water.[4][5] The guard may have also 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 perceived 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 could have accounted for one-fifth to one-third of the total length of a belemnite.[4]

Soft anatomy

Preserved soft body elements of the Late Jurassic Acanthoteuthis (above) and the Early Jurassic Passaloteuthis (below)

Belemnites had a

balance and function much like the cochlea of the ear – were large, much like in modern fast-moving squid.[7] Like other cephalopods, the skin was likely thin and slippery. The eyeballs were likely thicker, stronger, and more convex than in other cephalopods.[10]

The mantle cavity of cephalopods serves to contain the gills,

flying squid.[7]

Reconstruction of a typical belemnite

Limbs and hooks

Belemnites had 10 hooked arms of, more or less, equal length with suckers.

saber-like.[12] Overall, they were fish-hook shaped, and probably only the uncinus was exposed.[11]

Different hook shapes were probably specialized for certain tasks,[14] for example, a strongly hooked uncinus was designed to stab prey at a constant angle. It would force and sink in deeper if the prey tried to move away from the belemnite. Hook shapes and forms vary from species to species. In Chondroteuthis, large hooks were common near the mouth, and were either used for surrounding small prey or ramming into large prey; however, these large hooks were not present in a small specimen, indicating it was either a juvenile—and the development of different hooks coincided with a difference in prey selection - or the specimen was a female and the hooks were used by males for male-on-male combat or during copulation. In modern hook-bearing squid species, only matured males have hooks, indicating a reproductive purpose. It is possible the hooks, being analogous to suckers, could move.[12]

hectocotyli

The males, like in modern squid, probably had one or two

hectocotyli - long, modified arms used in copulation or combat with other males. Instead of several hooks, the hectocotyli feature a pair of enlarged hooks—mega-onychites—to latch onto the female at a safe distance to prevent getting stuck with one of her hooks. Like squid, the positioning of the mega-onychites could have been either at the tip or origin of the arm depending on the species. Copulation probably involved the male depositing spermatophores into the female's internal mantle chamber.[11]

Development

Oegopsina (J) Bactritida
. IC indicates the initial chamber.

Like other cephalopods, belemnites may have laid floating egg masses,[9] and a single female may have laid between 100 and 1,000 eggs.[15] Hatchlings were either miniature forms of adults or went through a larval stage. According to the latter model, the egg was formed by the protoconch and a single-layered shell wall. During the larval stage, the protoconch became internal and the guard began to form. The embryo of Passaloteuthis, the most well-studied among belemnite embryos, had a protoconch, a developing guard, and a solid guard. The developing guard tightly surrounded the protoconch. The embryonic shell consisted of an ovoid protoconch and several chambers. The protoconch had two layers, and several compartments - called "protoconch pockets" - formed between the layers, which may have stored gas or liquid in life to stay buoyant. The protoconch and guard were probably made of chitin, a protective material that may have allowed the embryo to survive at greater depths and colder temperatures, develop into adults faster, and allow juveniles and adults to venture into deeper waters.[16] Further, the protoconch would have allowed them to form limbs before reaching the phragmocone stage, and thus inhabit the open ocean earlier. These may have allowed belemnites to colonize a range of habitats across the world.[16][17]

Much like in cuttlefish, nautiluses, and

ammonites, the number and successive size of the chambers of the phragmocone are used to analyze the growth of an individual over their life. Successive belemnite chambers tend to increase in size exponentially. Unlike other cephalopods, there is no decreasing trend of chamber size in the earliest stages. The decreasing trend generally coincides with hatching, meaning embryonic belemnites had no or few chambers and hatched only with a protoconch. The phragmocone, thus, developed after hatching. Ammonites are thought to have done the same, implying a similar reproductive strategy, and, considering both reached cosmopolitan distributions, a rather efficient one. Belemnite hatchling protoconches are estimated to have been generally around 1.5 to 3 mm (0.059 to 0.118 in).[9]

The guards of

lunar cycle.[23]

Pathology

MRI of a deformed Late Cretaceous Gonioteuthis
guard

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 of the 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.[24] A Goniocamax guard has several blister-like formations, thought to have come from a polychaete flatworm infection.[25]

The calcitic guards were desirable habitats for boring parasites indicated by the diversity of trace fossils left on some guards, including the sponge Entobia, worm Trypanites, and barnacle Rogerella.[26][27]

Taxonomy

Evolution

Map of the world in the Late Triassic

Belemnites, being

Panthalassic Ocean around the eastern coasts of the ancient continent of Laurasia in a cephalopod radiation, alongside the octopus-like Prototeuthina and the belemnoid Phragmoteuthida.[29][19] However, there is a dubious Permian occurrence, the Palaeobelemnopsidae, reported from Southern China.[30] By the Early Jurassic, belemnites were probably quite common, having spread out into the western Laurasian coasts as well as Gondwanan waters to the south.[31][19]

Guard shapes in the early Jurassic ranged from conical to spearheaded but spearheaded became more prevalent as the Jurassic progressed. This was probably due to pressure to become more streamlined and increase swimming efficiency, coevolving with increasingly faster predators and competitors. Their early evolution and apparent abundance were likely important in reconstructing marine ecosystems after the Triassic–Jurassic extinction event, providing an ample food source for marine reptiles and sharks.[31]

Belemnoidea, as a group, seemed to feature a reduction of the projection of the otherwise conical phragmocone into the pro-ostracum. That of the most ancient order Aulacocerida is orthoconic (none projects), Phragmoteuthida three-quarters projects, Belemnitida a quarter, and the most developed Diplobelida an eighth.[32]

Research history

Opalized Peratobelus
guard from the Early Cretaceous

The first mention of belemnites in writing comes from the Greek philosopher

coral polyps, or some internal shell.[33]

In 1823, English naturalist

Karl Alfred Ritter von Zittel organized the clade Belemnoidea and included the families Belemnitidae, Asteroconites, and Xiphoteuthis.[35]

Hibolites from the early Cretaceous at the State Museum of Natural History Stuttgart

The guard—also known as the rostrum, scabbard, gaine, and sheath

segmented worm fossils have been mistaken for belemnite hooks and vice versa.[13] 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 carbon cycle.[7][36]

Phylogeny

Belemnites were

stem-group to Decapodiformes and Octopodiformes.[37]

Coleoidea
Coleoidea
Classification of Coleoidea according to Doyle 1994[37]

However, the higher classification of cephalopods is volatile with no clear consensus. Coleoidea is sometimes divided into

stem-group
of Decapodiformes:

Cephalopoda
Cephalopoda
Cephalopoda
Top: Belemnitida outside Decapodiformes.
stem-group of Decapodiformes[7]

According to the "belemnoid root-stock theory", belemnoids gave rise to modern coleoids sometime in the Mesozoic, with octopuses deriving from Phragmoteuthida and squid from Diplobelida, making Belemnoidea paraphyletic. The

transitional species between belemnoids and squid.[32] However, molecular evidence suggests that the squid and octopus lineage diverged from Belemnoidea in the Permian.[40]

Coleoidea
Coleoidea
"Belemnoid root-stock theory"[32][41]

The

suborders: Belemnitina and Belemnopseina, though a third possible suborder may exist with Sinobelemnitidae. The Belemnopseina guards have a groove on their alveolus, whereas the Belemnitina have a groove at their apex. The grooves probably corresponded to blood vessels.[29] Another suborder, Belemnotheutina, is also proposed, whose members have an aragonitic guard in contrast to the calcitic guards of other belemnites. Aragonitic guards are usually only seen in the ancestral Aulacocerida belemnoids, and Belemnotheutina may represent a transitional stage between the two orders, though some believe Belemnitida derived from Phragmoteuthida which derived from Aulacocerida.[8]

Belemnitida genera[42]

Paleoecology

Habitat

ammonites

Belemnite remains are found in what were

stenothermic, inhabiting only a narrow range of temperatures, though Neohibolites had a cosmopolitan distribution during the Cretaceous Thermal Maximum, a period of dramatic increase in global temperatures.[43]

Mortality

The shark Hybodus with belemnite guards in its stomach, State Museum of Natural History Stuttgart

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

ichthyosaurs; and the coprolite remains of ichthyosaurs and the extinct thylacocephalan crustaceans.[11] Some animals may have only eaten the heads, leaving the phragmocone and guards, however, the guards of around 250 Acrocoelites were found in the stomach of a 1.6 m (5 ft 3 in) Hybodus shark, and a fragment in an Oxford Clay marine crocodile, meaning they were eaten whole. It may be that they were to regurgitate the indigestible matter later, similar to the modern sperm whale.[44] To defend themselves, belemnites likely were able to eject a cloud of ink.[28]

The abundant planktonic belemnite larvae, along with planktonic ammonite larvae, likely formed the base of Mesozoic

pachycormid fish are thought to have been the main filter feeders of the time, occupying the same niche as modern baleen whales.[15]

A large aggregation of belemnite guards

Large accumulations of guards are commonly found and have been nicknamed "belemnite battlefields". The most quoted explanation is that belemnites were

spawning, much like modern coleoids which migrate from the ocean to the shelf area. In battlefields comprising both adults and juveniles—as the former model would consist entirely of adults—large groups of belemnites may have been killed by volcanism, changes in salinity or temperature, harmful algal blooms (and, thereby, anoxia), or mass stranding. Another popular theory is that the guards were simply moved or redeposited by ocean currents into large aggregations. Some battlefields may be regurgitated indigestible matter from a predator.[44]

Extinction

Squid and octopuses diversified and began to outcompete belemnites by the Late Jurassic to Early Cretaceous.[43][45] Belemnites declined through the Late Cretaceous, and their range became more restricted to the polar regions; the southern populations became extinct in the early Maastrichtian, and the last belemnites—of the family Belemnitellidae—inhabited what is now northern Europe.[46] They finally became extinct in the Cretaceous–Paleogene extinction event, around 66 mya, where, like in ammonites, it is thought the protoconch of embryos could not survive the ensuing acidification of the oceans.[9] However, the dubious genus Bayanoteuthis is reported from the Eocene, though this is often excluded from Belemnitida.[46][47]

Following the extinction of the belemnites at the end of the Cretaceous,

sea butterflies, replaced planktonic belemnite larvae at the base of the food chain.[15]

In culture

Belemnite guards have been known since antiquity, and much folklore has evolved since.

distemper in their horses.[49]

state fossil of Delaware on 2 July 1996.[50]

See also

References

  1. ^
    doi:10.1130/G33402.1
    .
  2. S2CID 252847710
    .
  3. ^ Wilkin, J.T.R. (2021). "Belemnites in Mythology: From Thunderstorms to Fertility Symbols". EGU Blog: Stratigraphy, Sedimentology and Palaeontology. Retrieved 2022-11-02.
  4. ^
    S2CID 129722176
    .
  5. ^
    ISBN 978-1-4443-1123-5
    .
  6. ^
    doi:10.1111/j.1475-4983.2010.01027.x
    .
  7. ^
    PMID 26740564
    .
  8. ^
    doi:10.1111/j.0031-0239.2004.00395.x
    .
  9. ^
    S2CID 89877678
    .
  10. ^
    S2CID 186210696
    .
  11. ^
    doi:10.1080/00288306.2010.526548
    .
  12. ^
    S2CID 89362515
    .
  13. ^
    S2CID 140173410
    .
  14. S2CID 134157665
    .
  15. ^
    PMID 29333344
    .
  16. ^
    doi:10.1111/let.12037
    .
  17. PMID 28560755
    .
  18. ^ Weis, R.; Mariotti, N. (2007). "A belemnite fauna from the Aalenian-Bajocian boundary beds of the Grand Duchy of Luxembourg (NE Paris Basin)". Bollettino della Società Paleontologica Italiana. 46 (2–3): 166.
  19. ^
    S2CID 55001872
    .
  20. ^ "Belemnites". British Geological Survey. Retrieved 10 February 2019.
  21. ^
    S2CID 140647091
    .
  22. ^ Wierzbowski, H. (2013). "Life span and growth rate of Middle Jurassic mesohibolitid belemnites deduced from rostrum microincrements" (PDF). Volumina Jurassica. 11: 1–18.
  23. ^ Dunca, E.; Doguzhaeva, L.; Schöne, B. R.; van de Schootbrugge, B. (2006). "Growth patterns in rostra of the Middle Jurassic belemnite Megateuthis giganteus: Controlled by the moon?". Acta Universitatis Carolinae - Geologica. 49 (1): 107–117.
  24. doi:10.5194/bg-2-133-2005.{{cite journal}}: CS1 maint: numeric names: authors list (link
    )
  25. doi:10.1127/njgpa/2018/0720
    .
  26. S2CID 133806985
    .
  27. doi:10.5194/fr-20-173-2017
    .
  28. ^
    ISBN 978-0-07-179273-8
    .
  29. ^
    PMID 24788872
    .
  30. ^ Chen, T.; Sen, Z. (1982). "Discovery of Permian belemnoids in South China with comments on the origin of the Coleoidea". Acta Palaeontologica Sinica. 21: 181–190.
  31. ^
    doi:10.1016/j.palaeo.2016.05.029
    .
  32. ^
    doi:10.1111/pala.12036
    .
  33. ^ a b c d de Blainville, H. M. D. (1827). Mémoire sur les bélemnites, considérées zoologiquement et géologiquement [Memorandum on belemnites, considered zoologically and geologically]. Paris F.G. Levrault. pp. 2–25.
  34. ^
    S2CID 140623418
    .
  35. ^
    von Zittel, K. A. (1895). "Mollusca"
    . Grundzüge der Paläontologie (Paläozoologie) [Main features of paleontology (paleozoology)] (in German). München, Leipzig, Druck, and Verlag von R. Oldenbourg. pp. 470–478.
  36. doi:10.1111/let.12076
    .
  37. ^ a b Doyle, P.; Donovan, D. T.; Nixon, M. (1994). "Phylogeny and systematics of the Coleoidea". University of Kansas Paleontological Contributions (5).
  38. doi:10.1093/mollus/eyq032
    .
  39. S2CID 2767810
    .
  40. S2CID 86869162
    .
  41. doi:10.1111/let.12155
    .
  42. ^ "Taxon Tree at Family Level". Worldwide Mollusc Species Data Base. Retrieved 12 June 2019.
  43. ^
    doi:10.1130/G31724.1
    .
  44. ^
    doi:10.1111/j.1502-3931.1993.tb01513.x
    .
  45. PMID 28250188
    .
  46. ^
    S2CID 129654916
    .
  47. doi:10.1127/njgpa/164/1982/156
    .
  48. ^
    S2CID 86706625
    .
  49. ^ van der Geer, A. A.; Dermitzakis, M. D. (2008). "Fossil medicines from 'snake egg' to 'Saint's bones'; an overview". Calicut Medical Journal. 6 (1): 4.
  50. ^ "Delaware state fossil - the belemnite". Delaware Geological Survey. Retrieved 10 February 2019.

External links

Retrieved from "https://en.wikipedia.org/w/index.php?title=Belemnitida&oldid=1210825420"