Did you know that there is only one shark species where the males look different than the females (in addition to the claspers, of course), a phenomenon called sexual dimorphism? The adult male of the bonnethead sharks, a species of hammerhead sharks, has got a distinct bulge at the front of its hammer, whereas the female has got a rounded one.

Compared to all other hammerheads, bonnethead sharks have not only a much smaller hammer (that’s why they are called bonnethead or shovelhead) but more developed pectoral fins which they are using actively for swimming (unlike all other hammerheads). Since the archetype of a hammerhead shark had a really big winglike hammer, is is assumed that the smaller hammer of the bonnethead sharks means that they are the more recent development in the evolution.

Bonnethead sharks live in warm shallow seas and estuaries along Americas coasts on both sides of the equator. Like other hammerheads they swim in groups: smaller ones of 5 to 15 individuals, but also bigger schools of hundreds or even thousands sharks. They practice a complex social behavior with a size-related dominance hierarchy (by the way, females get larger than males in all shark species) and extensive body language.

Mostly Crustaceans, but also large amount of seaweed have been found in the stomach of bonnetheads. It is unknown if the seaweed has been consumed incidentally during feeding or if the shark can digest it or uses it to help move food and indigestible bits in its bowels.

Bonnethead sharks are up to 5 ft -1.5 m- long, with an average of 2 to 3 ft -0.61 to 0.91 m. They are ovoviviparous and give birth to four to twelve cute little pups (measuring 12 inches -33 cm). In 2001, a female bonnethead has been found to produce a pup by parthenogenesis (that means asexually reproducing), like in blacktip sharks and zebra sharks. But this is no solution for the dramatic shrinking number of sharks in the sea in general (resulting in a lesser chance to find a partner), since parthenogenesis, more common in baser animals, reduces the genetic diversity and makes the sharks less fit to overcome future selective pressures.

Sources: herehere and here

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