Contents

Bullhead shark

Bullhead shark Temporal range: Late Jurassic–Present PreꞒ Ꞓ O S D C P T J K Pg N
Horn shark, Heterodontus francisci
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Clade:	Neoselachii
Subdivision:	Selachimorpha
Superorder:	Galeomorphii
Order:	Heterodontiformes
Family:	Heterodontidae J. E. Gray, 1851
Genus:	Heterodontus Blainville, 1816
Type species
Squalus portusjacksoni F. A. A. Meyer, 1793
Species
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.^[1] 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.^[2]

The bullhead sharks are characterised by a broad head, heavy brow, stubby snout and small mouth. The mouth is located entirely anterior to the eye sockets, due to their protruding jaw structure. They have a distinct groove from their nostrils to their mouths. They grow to about a meter in size, with the largest species being that of the Port Jackson shark. The eyes lack a nictitating membrane. A spiracle is present, but small. The dorsal ends of the fourth and fifth branchial arches are attached, but not fused into a "pickaxe" as in lamniform sharks. Heterodontiforms have two dorsal fins, with fin spines, as well as an anal fin. The dorsal and anal fins also contain basal cartilages, not just fin rays.^[1]

Ten living species of bullhead shark have been described:

• Heterodontus francisci (Girard, 1855) (horn shark)
• Heterodontus galeatus (Günther, 1870) (crested bullhead shark)
• Heterodontus japonicus (Maclay & W. J. Macleay, 1884) (Japanese bullhead shark)
• Heterodontus marshallae White, Mollen, O'Neill, Yang & Naylor, 2023 (painted hornshark)
• Heterodontus mexicanus (L. R. Taylor & Castro-Aguirre, 1972) (Mexican hornshark)
• Heterodontus omanensis (Z. H. Baldwin, 2005) (Oman bullhead shark)
• Heterodontus portusjacksoni (F. A. A. Meyer, 1793) (Port Jackson shark)
• Heterodontus quoyi (Fréminville, 1840) (Galapagos bullhead shark)
• Heterodontus ramalheira (J. L. B. Smith, 1949) (whitespotted bullhead shark)
• Heterodontus zebra (J. E. Gray, 1831) (zebra bullhead shark)

• 
  APort Jackson shark, Heterodontus portusjacksoni
• 
  Dentition and oronasal grooves of a Port Jackson shark
• 
  Zebra bullhead shark, Heterodontus zebra

• List of prehistoric cartilaginous fish

• Compagno, Leonard (2002) Sharks of the World: Bullhead, mackerel and carpet sharks Volume 2, FAO Species Catalogue, Rome. ISBN 92-5-104543-7.