| Bullhead shark Temporal range:
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|---|---|
.JPG)
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| Horn shark, Heterodontus francisci | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Division: | Selachii |
| Superorder: | Galeomorphii |
| Order: | Heterodontiformes |
| Family: | Heterodontidae J. E. Gray, 1851 |
| Genus: | Heterodontus Blainville, 1816 |
| Type species | |
| Squalus portusjacksoni F. A. A. Meyer, 1793
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| Species | |
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See text | |
The bullhead sharks are members of the genus Heterodontus, the only members of the family Heterodontidae and only living members of the order Heterodontiformes. All are relatively small, with the largest species reaching just 1.65 metres (5.5 ft) in maximum length. They are bottom feeders in tropical and subtropical waters.
The Heterodontiforms appear in the fossil record in the Early Jurassic. The oldest fossils of the modern genus date to the Late Jurassic. Despite the very ancient origins of this genus and its abundance in the fossil record, phylogenetic evidence indicates that all extant species in the genus arose from a single common ancestor that survived the Cretaceous-Paleogene extinction, with diversification into modern species only starting around the mid-Eocene.[1]
- ^ Slater, Tiffany S.; Ashbrook, Kate; Kriwet, Jürgen (2020). Cavin, Lionel (ed.). "Evolutionary relationships among bullhead sharks (Chondrichthyes, Heterodontiformes)". Papers in Palaeontology. 6 (3): 425–437. Bibcode:2020PPal....6..425S. doi:10.1002/spp2.1299. hdl:10468/10339. ISSN 2056-2799.