Bullhead shark
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| Bullhead sharks Fossil range: 174–0 Ma Late Toarcian to Present[1] |
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 Two Port Jackson sharks (Heterodontus portusjacksoni)
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The bullhead sharks are a small order (Heterodontiformes) of basal modern sharks (Neoselachii). There are nine living species in a single genus, Heterodontus, in the family Heterodontidae. All are relatively small, with the largest species being just 150 centimetres (59 in) in adult length. They are bottom feeders in tropical and subtropical waters.
The Heterodontiforms appear in the fossil record in the Early Jurassic, well before any of the other Galeomorphii, a group which includes all modern sharks except the dogfish and its relatives. However, they have never been common, and it is likely their origin lies even further back.
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[edit] Description
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This section contains too much jargon and may need simplification or further explanation. Please discuss this issue on the talk page, and/or remove or explain jargon terms used in the article. Editing help is available. (January 2009) |
The Heterodontiforms are morphologically rather distinctive. The mouth is located entirely anterior to the orbits. Labial cartilages are found in the most anterior part of the mouth. Nasoral grooves are present, connecting the external nares to the mouth. The nasal capsules are "trumpet-shaped" & well-separated from orbits. Circumnarial skin folds present; but the rostral process of neurocranium (braincase) absent, although a precerebral fossa is present. Finally, the braincase bears a supraorbital crest.
The eyes lack a nictitating membrane. A spiracle is present, but small. The dorsal ends of branchial arches 4 and 5 are attached, but not fused into a "pickaxe" as in lamniform sharks. Heterodontiforms have 2 dorsal fins, with fin spines, as well as an anal fin. The dorsal and anal fin also contain basal cartilages, not just fin rays.
[edit] Species
There are nine living species of bullhead shark:
- Horn shark, Heterodontus francisci (Girard, 1855) [2]
- Crested bullhead shark, Heterodontus galeatus (Günther, 1870) [3]
- Japanese bullhead shark, Heterodontus japonicus Maclay & Macleay, 1884 [4]
- Mexican hornshark, Heterodontus mexicanus Taylor & Castro-Aguirre, 1972 [5]
- Oman bullhead shark, Heterodontus omanensis Baldwin, 2005
- Port Jackson shark, Heterodontus portusjacksoni (Meyer, 1793) [6]
- Galapagos bullhead shark, Heterodontus quoyi (Fréminville, 1840) [7]
- Whitespotted bullhead shark, Heterodontus ramalheira (Smith, 1949) [8]
- Zebra bullhead shark, Heterodontus zebra (Gray, 1831) [9]
[edit] See also
[edit] References
- ^ Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (Chondrichthyes entry)". Bulletins of American Paleontology 364: p.560. http://strata.ummp.lsa.umich.edu/jack/showgenera.php?taxon=575&rank=class. Retrieved on 2008-01-09.
- ^ FishBase
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- Heterodontus (TSN 159790). Integrated Taxonomic Information System. Retrieved on 4 May 2006.
- "Heterodontus". FishBase. Ed. Ranier Froese and Daniel Pauly. May 2006 version. N.p.: FishBase, 2006.
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