Sphyrnidae

Scalloped hammerhead shark Sphyrna lewini, copyright NOAA Photo Library.

Belongs within: Carcharhiniformes.

The Sphyrnidae, hammerhead sharks, are a group of actively swimming sharks in which the head has been expanded laterally into a mallet- or hammer-like shape.

Characters (from Compagno 1984): Head with laterally expanded blades, shaped like a double-bitted axe or mallet in profile; eyes circular or nearly so; nictitating eyelids internal; spiracles absent; anterior nasal flaps short and triangular, not barbel-like; internarial width usually about 7 to 14 times the nostril width (but only 1.1 to 1.3 times it in Eusphyra, which has tremendously expanded nostrils); labial furrows vestigial or absent; teeth small to moderately large, more or less bladelike, with acute and narrow to moderately broad cusps, no lateral cusplets, and with basal ledges and grooves strong to absent; teeth weakly differentiated in upper and lower jaws; tooth rows 24 to 37/25 to 37. Precaudal pits present. First dorsal fin moderate-sized to very large but not keel-like, much shorter than caudal fin; first dorsal base ahead of pelvic bases, varying from equidistant between pectoral and pelvic bases to closer to pectoral bases; midpoint of first dorsal base always in front of pelvic origins; second dorsal fin much smaller than first; pectoral fins with radials extending into distal web of fins. Ventral caudal lobe strong, undulations or ripples present in dorsal caudal margin. Neurocranium without primary supraorbital crests, but with tips of preorbital and postorbital processes fused to form unique secondary supraorbital crests; vertebral centra with strong, wedge-shaped intermedial calcifications. Valvular intestine with a scroll valve. Colour light grey or brownish above, white below, no colour pattern. Development viviparous.

<==Sphyrnidae [Cestraciontoidae, Zyganinae] C84
    |--Eusphyra Gill 1862 C84
    |    `--*E. blochii (Cuvier 1817) (see below for synonymy) C84
    `--Sphyrna Rafinesque 1810 (see below for synonymy) C84
         |  i. s.: S. arambourgi Cappetta 1970 CDZ93
         |--S. (Sphyrna) C84
         |    |--*S. (S.) zygaena (Linnaeus 1758) (see below for synonymy) C84
         |    |--S. (S.) couardi Cadenat 1950 C84
         |    |--S. (S.) lewini (Griffith & Smith 1834) (see below for synonymy) C84
         |    `--S. (S.) mokarran (Rüppell 1837) (see below for synonymy) C84
         `--S. (Platysqualus Swainson 1839) C84
              |--S. (P.) corona Springer 1940 C84
              |--S. (P.) media Springer 1940 [incl. S. nana Sadowsky 1965] C84
              |--S. (P.) tiburo (Linnaeus 1758) [=Squalus tiburo; incl. Sp. vespertina Springer 1940] C84
              `--S. (P.) tudes (Valenciennes 1822) [=Zygaena tudes; incl. S. bigelowi Springer 1944] C84

*Eusphyra blochii (Cuvier 1817) [=Zygaena blochii, Sphyrna blochii; incl. Z. laticeps Cantor 1837, Z. latycephala van Hasselt 1823] C84

Sphyrna Rafinesque 1810 [incl. Cestracion Gill 1862, Cestrorhinus Blainville 1816, Reniceps Gill 1862, Sphyra van der Hoeven 1855, Sphyrichthys Thienemann 1828, Sphyrnias Rafinesque 1815, Zygaena Cuvier 1817, Zygoena Risso 1826] C84

Sphyrna (Sphyrna) lewini (Griffith & Smith 1834) [=Zygaena lewini; incl. S. diplana Springer 1941, Z. erythraea Hemprich & Ehrenberg 1899, Z. indica van Hassel 1823, Cestracion leeuwenii Day 1865, Z. malleus Valenciennes 1822, C. oceanica Garman 1913] C84

Sphyrna (Sphyrna) mokarran (Rüppell 1837) [=Zygaena mokarran; incl. Z. dissimilis Murray 1887, Sphyrna ligo Fraser-Brunner 1950] C84

*Sphyrna (Sphyrna) zygaena (Linnaeus 1758) [=Squalus zygaena, Sq. (Zygaena) zygaena; incl. Sq. (Cestrorhinus) caroliniensis Blainville 1816 (n. n.) Sq. malleus Shaw & Nodder 1796, Sq. (C.) pictus Blainville 1816 (n. n.), Zygaena subarcuata Storer 1848, Z. vulgaris Cloquet 1830] C84

*Type species of generic name indicated

REFERENCES

[CDZ93] Cappetta, H., C. Duffin & J. Zidek. 1993. Chondrichthyes. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 593–609. Chapman & Hall: London.

[C84] Compagno, L. J. V. 1984. FAO Species Catalogue vol. 4. Sharks of the World: An annotated and illustrated catalogue of shark species known to date. Part 2—Carcharhiniformes. United Nations Development Programme, Food and Agriculture Organization of the United Nations: Rome.