Our classical view of the shape of an organism's head is round or ovoid. Some species, however, have evolved completely different shapes, with some shapes being quite remarkable. For instance, one of the largest predators in the oceans has evolved a hammer-shaped head🔨. Globally, a total of 10 species of hammerhead sharks have been described. Here, at the HKBM, we are fortunate to have a specimen of the scalloped hammerhead shark (𝘚𝘱𝘩𝘺𝘳𝘯𝘢 𝘭𝘦𝘸𝘪𝘯𝘪 (Griffith & Smith, 1834)) to show you. Interestingly, this species has almost the same head shape than the Carolina Hammerhead (𝘚𝘱𝘩𝘺𝘳𝘯𝘢 𝘨𝘪𝘭𝘣𝘦𝘳𝘵𝘪) 😯while the other 8 species have quite distinguishable cephalofoil (head shape) (see picture).
Some studies suggest that the head of hammerhead sharks contain a higher density of electrosensory pores in comparison to other pointed-head sharks, conferring them with a higher accuracy and efficiency in tracking their prey. Most sharks can only tilt their heads slightly upwards while hammerhead sharks are able to move theirs up and down to a certain degree. This higher maneuverability in vertical motion helps them to capture prey from the seabed.
With their eyes located on the side of the head, some of you may be wondering: can they see in front of them🤔? Surprisingly, yes! Their field of vision overlaps to an even greater extent than other sharks, providing them with 360 degrees of vision. That may also be the reason why they develop a hammer-like shaped head (and something encountered in other groups of organisms such as the stalk-eyed flies of the 𝘋𝘪𝘰𝘱𝘴𝘪𝘥𝘢𝘦 family, among others…).
Scalloped hammerhead sharks are schooling animals which prey on other schooling fishes and squids. Sometimes they stay on the surface when traveling in the ocean under the sunlight☀; but did you know that sharks can get suntanned too? A study on scalloped hammerhead sharks shows that there is an increase in melanin (dark pigment) when exposed to direct sunlight. This is the first time suntanning is documented in aquatic vertebrates! Furthermore, no damage or signs of skin cancer appeared. This valuable information opens a new path for studying medication or prevention of skin cancer in the future.
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