Belemnitida
Belemnites | |
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The Early Jurassic Passaloteuthis bisulcata showing soft anatomy | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Mollusca |
Class: | Cephalopoda |
Superorder: | †Belemnoidea |
Order: | †Belemnitida Zittel , 1895
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Suborders | |
Belemnitida (or belemnites) is an
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
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
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
The dense guard probably served to
Soft anatomy
Belemnites had a
The mantle cavity of cephalopods serves to contain the gills,
Limbs and hooks
Belemnites had 10 hooked arms of, more or less, equal length with suckers.
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]
The males, like in modern squid, probably had one or two
Development
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
The guards of
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 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
Belemnites, being
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
The first mention of belemnites in writing comes from the Greek philosopher
In 1823, English naturalist
The guard—also known as the rostrum, scabbard, gaine, and sheath
Phylogeny
Belemnites were
Coleoidea | |||||||||||||||||||||
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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
Cephalopoda
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Top: Belemnitida outside Decapodiformes. stem-group of Decapodiformes[7]
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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
Coleoidea | |||||||||||||||||||||||||||
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"Belemnoid root-stock theory"[32][41] |
The
Belemnitida genera[42]
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Paleoecology
Habitat
Belemnite remains are found in what were
Mortality
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
The abundant planktonic belemnite larvae, along with planktonic ammonite larvae, likely formed the base of Mesozoic
Large accumulations of guards are commonly found and have been nicknamed "belemnite battlefields". The most quoted explanation is that belemnites were
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,
In culture
Belemnite guards have been known since antiquity, and much folklore has evolved since.
See also
References
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- ^ 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.
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- ^ Wierzbowski, H. (2013). "Life span and growth rate of Middle Jurassic mesohibolitid belemnites deduced from rostrum microincrements" (PDF). Volumina Jurassica. 11: 1–18.
- ^ 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.
- doi:10.5194/bg-2-133-2005.)
{{cite journal}}
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- ^ ISBN 978-0-07-179273-8.
- ^ PMID 24788872.
- ^ 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.
- ^ .
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- ^ 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.
- ^ S2CID 140623418.
- ^ 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.
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- ^ a b Doyle, P.; Donovan, D. T.; Nixon, M. (1994). "Phylogeny and systematics of the Coleoidea". University of Kansas Paleontological Contributions (5).
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- ^ "Taxon Tree at Family Level". Worldwide Mollusc Species Data Base. Retrieved 12 June 2019.
- ^ doi:10.1130/G31724.1.
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- ^ 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.
- ^ "Delaware state fossil - the belemnite". Delaware Geological Survey. Retrieved 10 February 2019.
External links
- Media related to Belemnitida at Wikimedia Commons