Elasmobranchii
| Elasmobranchii Fossil range: Late Silurian–Recent [1] |
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|---|---|
 |
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| Great white shark, Carcharodon carcharias | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii Bonaparte, 1838 |
| Superorders | |
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Batoidea (rays and skates) |
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Elasmobranchii (pronounced /ɛˌlæzmɵˈbræŋki.aɪ/) is a subclass of Chondrichthyes or cartilaginous fishes, that includes the sharks (Selachimorpha) and the rays and skates (Batoidea).
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Evolution
Fossilised shark teeth are known from the early Devonian, around 400 million years ago. During the following Carboniferous period, the sharks underwent a period of diversification, with many new forms evolving. Many of these became extinct during the Permian, but the remaining sharks underwent a second burst of adaptive radiation during the Jurassic, around which time the skates and rays first appeared. Many surviving orders of elasmobranch date back to the Cretaceous, or earlier.[2]
Description
Elasmobranchii is one of the two subclasses of cartilaginous fish in the class Chondrichthyes, the other being Holocephali (chimaeras). For features that distinguish Elasmobranchii from Holocephali, see those articles. This classification includes great white sharks and the extinct megalodon.
Members of the elasmobranchii subclass have no swim bladders, five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins, and small placoid scales. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The eyes have a tapetum lucidum. The inner margin of each pelvic fin in the male fish is grooved to constitute a clasper for the transmission of sperm. These fish are widely distributed in tropical and temperate waters.[3]
Taxonomy
Nelson's 2006 Fishes of the World arranges the class as follows:
- Subclass Elasmobranchii
- †Plesioselachus
- †Order Squatinactiformes
- †Order Protacrodontiformes
- †Infraclass Cladoselachimorpha
- †Order Cladoselachiformes
- †Infraclass Xenacanthimorpha
- †Order Xenacanthiformes
- Infraclass Euselachii (sharks and rays)
- †Order Ctenacanthiformes
- †Division Hybodonta
- †Order Hybodontiformes
- Division Neoselachii
- Subdivision Selachii (modern sharks)
- Superorder Galeomorphi
- Order Heterodontiformes (bullhead sharks)
- Order Orectolobiformes (carpet sharks)
- Order Lamniformes (mackerel sharks)
- Order Carcharhinidae (ground sharks)
- Superorder Squalomorphi
- Order Hexanchiformes (frilled and cow sharks)
- Order Echinorhiniformes (bramble sharks)
- Order Squaliformes (dogfish sharks)
- †Order Protospinaciformes
- Order Squatiniformes (angel sharks)
- Order Pristiophoriformes (sawsharks)
- Superorder Galeomorphi
- Subdivision Batoidea (rays)
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- Order Torpediniformes (electric rays)
- Order Pristiformes (sawfishes)
- Order Rajiformes (skates and relatives)
- Order Myliobatiformes (stingrays and relatives)
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- Subdivision Selachii (modern sharks)
References
- ^ Karatajūte, V. (1973). "Elegestolepis grossi ge. et sp. nov., ein neues typ der placoidschuppe aus dem oberen Silur der Tuwa.". Palaeontographica Abteilung A 143: 35–50.
- ^ Palmer, D., ed (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 26. ISBN 1-84028-152-9.
- ^ Bigelow, Henry B.; Schroeder, William C. (1948). Fishes of the Western North Atlantic. Sears Foundation for Marine Research, Yale University. pp. 64–65. ISBN B000J0D9X6.
