It’s hammerhead time!

One of the smaller hammerhead sharks,
Sphyrna tutus (Figs. 1, 2), enters the LRT alongside Isurus, the mako shark. No surprise. The interesting thing about hammerhead sharks is their heads! What is going on inside that sharkskin?

Figure 1. The small hammerhead shark, Sphyrna tutus, is best appreciated in dorsal or ventral view.

Figure 1. The small hammerhead shark, Sphyrna tutus, is best appreciated in dorsal or ventral view.

In hammerhead sharks of all sorts,
the eyes and nares are widely separated by the lateral expansion of the nasals, prefrontals and postfrontals creating the classic hammerhead cephalofoil (Fig. 2), made entirely of cartilage, not bone. Even so, each piece has a bone analog, despite the fusion of several elements, especially in the jaws (Figs. 1, 2).

Figure 2. Skull of Sphyrna tutus in three views from Digimorph. org and used with permission. Colors added.

Figure 2. Cartilaginous skull of Sphyrna tutus in three views from Digimorph. org and used with permission. Colors added.

Sphyrna tudes (orignally Zygaena tudes Valenciennes 1822; 1.3m in length) is the extant smalleye hammerhead shark. It prefers muddy habitats with poor visibility. As a juvenile Sphyrna prefers shrimp, then grows up to prefer catfish eggs. Gestation is 10 months. Females produce 19 pups each year.


References
Valenciennes A 1822. Sur le sous-genre Marteau, Zygaena. Memoires du Museum National d’Histoire Naturelle. 9: 222–228.

wiki/Sphyrna

 

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