Bullhead shark
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 Two Port Jackson sharks (Heterodontus portusjacksoni)
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The bullhead sharks are a small order (Heterodontiformes) of very basal (primitive) modern sharks (Neoselachii). There are nine living species in a single genus, Heterodontus, in the family Heterodontidae. All are relatively small (50 to 150 cm) bottom feeders in tropical and subtropical waters.
The symbol '$' below indicates a synapomorphy, (a character believed to be uniquely present in the last common ancestor of all heterodontiforms).
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.
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.
[edit] Species
- Horn shark, Heterodontus francisci (Girard, 1855) [1]
- Crested bullhead shark, Heterodontus galeatus (Günther, 1870) [2]
- Japanese bullhead shark, Heterodontus japonicus Maclay & Macleay, 1884 [3]
- Mexican hornshark, Heterodontus mexicanus Taylor & Castro-Aguirre, 1972 [4]
- Oman bullhead shark, Heterodontus omanensis Baldwin, 2005
- Port Jackson shark, Heterodontus portusjacksoni (Meyer, 1793) [5]
- Galapagos bullhead shark, Heterodontus quoyi (Fréminville, 1840) [6]
- Whitespotted bullhead shark, Heterodontus ramalheira (Smith, 1949) [7]
- Zebra bullhead shark, Heterodontus zebra (Gray, 1831) [8]
[edit] References
- Heterodontus (TSN 159790). Integrated Taxonomic Information System. Accessed on 4 May 2006.
- "Leptonotus". FishBase. Ed. Ranier Froese and Daniel Pauly. May 2006 version. N.p.: FishBase, 2006.
