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Why do hammerheads have hammer heads?

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A great hammerhead shark (Sphyrna mokarran). If you look closely, you can spot small black dots along the broad head that are Ampullae of Lorenzini, which detect electrical impulses emitted by potential prey. Photo credit: Albert Kok.
A great hammerhead shark (Sphyrna mokarran). If you look closely, you can spot small black dots along the broad head that are Ampullae of Lorenzini, which detect electrical impulses emitted by potential prey. Photo credit: Albert Kok.

By Blaise Jones

When people picture sharks, they probably imagine a sleek, torpedo-shaped body with a conical head. Most sharks stick to this biological shape and for good reason. The typical shark body shape is perfectly adapted, allowing them to move quickly through the water with minimal effort. So why do hammerhead sharks have such an odd deviation from the norm?

Global distribution of hammerhead sharks. Image credit: Chris Huh.
Global distribution of hammerhead sharks. Image credit: Chris Huh.

There are three main theories as to why hammerhead sharks have their famous head shape. The first is the enhanced vision theory. It was found in an experiment performed for the Journal of Experimental Biology that hammerhead sharks have an increased field of vision directly proportional to the size of the shark’s head. Hammerhead species with larger heads can see more both vertically and horizontally when compared to both smaller hammerheads and non-hammerhead sharks. Additionally, hammerhead sharks perform an exaggerated swinging of the head back and forth as they swim, giving them a full 360-degree field of vision as they hunt for their prey.

The second theory is the enhanced electroreception theory. Hammerhead sharks, like all shark species, have a special sensory system known as the Ampullae of Lorenzini. Shark’s snouts are covered in hundreds of tiny gel-filled pores. These pores detect the bioelectrical signals that all living things produce as they move. These sensors are so sensitive that they can detect half a billionth of a volt! This allows sharks to detect the electrical signals of an animal’s heartbeat.

It is thought that hammerheads’ wide heads give them a wider surface area in which to house these sensors, giving them a wider area with which to scan the bottom. Most hammerhead sharks are bottom feeders, hunting stingrays, squid, and crustaceans that like to hide beneath the sand. Therefore, having a built in biological “electrical detector” allows hammerhead sharks to find their hidden prey with relative ease. They then use their heads to pin the prey to the bottom, before tearing into them with their jaws.

The third theory as to why hammerhead sharks have their uniquely-shaped head is that it enhances maneuverability, and may make swimming easier. The theory states that the wide head serves as a canard wing of sorts while the shark swims, generating lift and making it easier for the shark to keep from sinking. Like most sharks, hammerheads need to keep swimming to breathe. Any adaptation that makes swimming easier would be hugely advantageous. This third theory is also supported by the fact that hammerhead sharks have extra muscles between the head and vertebral column, giving the head-end greater maneuverability. On top of allowing them to swim with less effort, the unusually-shaped head increases movability, which is invaluable for a predator that hunts quick moving, bottom-dwelling prey.

While there is no single reason for the shape of a hammerhead shark’s head, there is more than enough evidence to show that despite its ungainly appearance, the hammerhead’s hammerhead is a highly specialized, incredibly useful adaptation. It just goes to show that even the body of a shark has room for improvement.

 

SOURCES:

“Hammerhead Shark.” Aquatic Community. N.p., n.d. Web. 15 Oct. 2015. <http://www.aquaticcommunity.com/sharkfish/hammerheadshark.php>.

“Hammerhead Shark.” National Geographic. N.p., n.d. Web. 15 Oct. 2015. <http://animals.nationalgeographic.com/animals/fish/hammerhead-shark/>.

McComb, D. M., T. C. Tricas, and S. M. Kajiura. “Enhanced visual fields in hammerhead sharks.” Journal of Experimental Biology 212 (2009): 4010-18. <http://jeb.biologists.org/content/212/24/4010#skip-link>

“Why Do Hammerheads Have Hammer Heads?” Reef Check. N.p., n.d. Web. 15 Oct. 2015. <http://www.reefcheck.org/news/news_detail.php?id=816>.

 

 
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