Hammerhead sharks (Sphyra) are one of the most distinguishable sharks in the oceans. This is due to the hammerhead shark’s famous head shape. Unlike most sharks, these sharks have a rectangular head with eyes far spread out on each end. This unique characteristic makes them well-adapted predators. Having their eyes so far apart grants this shark a 360-degree view of its surroundings. A common question surrounding these sharks is whether or not they have always had these famous heads. Also, why do these sharks have this unique head shape and what sort of benefits does it provide? This blog aims to answer those questions and share some interesting facts about this incredible shark.
Hammerhead Shark’s Head Evolution
Hammerheads come from a larger ancestor, one that did not necessarily possess its now famous head.
©Gary J. Wood from Toronto, ON, Canada, CC BY-SA 2.0, via Wikimedia Commons – Original / License
Hammerhead sharks have been in the ocean for about 20 million years. Their famous head shape has been studied for the past 50 years. The ancestors of the hammerhead shark did not possess the current hammerhead shark’s head shape, but rather, that developed over time. In a recent study, DNA from eight of the ten species of hammerhead sharks was studied. The information gathered from that study not only showed that some of the smaller species of hammerheads came from a larger ancestor, but also that each species evolved differently due to environmental pressures.
The DNA collected from this study showed that the larger hammerheads evolved into smaller hammerheads, while the smaller species evolved on their own twice. In addition — although their head shapes may have changed and varied externally — the volume of all internal parts within the skull did not change.
Reasons for Evolution
There are various hypotheses for why the hammerhead shark’s heads evolved in the way that they did. One of those theories revolves around enhanced electrosensory. Having these larger and flatter heads allows more space for the electroreceptors to spread out, thus allowing hammerheads to search for food in wider areas more easily.
Another theory is that they needed enhanced vision. Hammerheads have enhanced vision because their eyes are at the far end of the cephalofoil, the two outward parts of their heads. They have great depth perception and fantastic binocular vision. Although they do possess a blind spot.
A third theory for why hammerhead sharks evolved the way they did is that they needed to move faster and more efficiently when swimming. The unique head provides them with a lift while swimming. This makes it much easier for them to move in the water. Hammerheads also have more muscles in their head than other sharks, allowing for easier mobility and flexibility with their head movement.
Other Advantages of Hammerhead Physiology
Hammerhead Eyes
The shark’s unique head shape allows its sensory organs to spread out throughout its head. This allows them to better detect their prey with their strong binocular vision. In fact, they can track fast-moving prey even if it is not directly in front of them. However, even with their enhanced vision, they do possess one blind spot. Hammerhead sharks cannot see directly in front of their nose.
In addition to detecting their prey, their heads also allow them to better trap it. These sharks use the weight of their massive heads to help hold the prey in place as they consume it.
Hammerhead Swimming
In addition to improved eyesight, their head shape also provides some hammerheads with increased navigational abilities. However, head size does not benefit all species to the same degree. The head of larger species is similar to a wing of a plane and allows them better movement in the water. The smaller species don’t have the same benefit, but they still have enhanced vision and prey detection.
Apart from their unique head shapes, hammerhead sharks’ fins also differ from other sharks. Most sharks have pectoral fins that are longer than their dorsal fins. With hammerhead sharks, it is the opposite. They possess a very long dorsal fin and that affects how they swim. Hammerheads are frequently seen swimming on their side. These sharks spend about 90 percent of their time swimming on their side. Swimming like this seems to increase their swimming efficiency.
Hammerhead Shark Size
Apart from these creatures’ heads, they also stand out because of their large size. The largest hammerhead ever recorded measured around 20 feet long. However, the average hammerhead typically ranges between 11-13 feet in length. The great hammerhead is the only shark of the ten species that is large enough to pose a threat to humans.
Hammerhead Shark Diet
Due to their smaller mouth size, the hammerhead shark’s dining options are more limited than other shark species. However, their smaller mouth size does nothing to deter them from feasting on a variety of ocean wildlife. While their preferred food source is stingrays, they do also enjoy various fish, squid, crustaceans, and occasionally seagrass. Certain species can even be cannibalistic at times!
Hammerhead Shark Species
Although smooth hammerhead sharks possess the signature head, theirs are more rounded rather than rectangular.
©iStock.com/Michael Zeigler
There are 10 species of this shark, but the most well-known of them all is the great hammerhead. The table below gives a brief overview of some of the key differences between each of the hammerhead shark species.
| Shark Name | Scientific Name | Size | Fun Fact |
|---|---|---|---|
| Great Hammerhead | Sphyrna mokarran | 10-14 feet long | These sharks consume hammerheads as well as their own young. |
| Smooth Hammerhead | Sphyrna zygaena | 10-14 feet long | They have rounded heads. |
| Whitefin Hammerhead | Sphyrna couardi | 5-6 feet long | They have a sophisticated palate. they prefer crabs, lobsters, squids, and octopuses. |
| Smalleye Hammerhead | Sphyrna tudes | 4-5 feet long | Also known as the golden hammerhead due to its golden color. |
| Bonnethead Hammerhead | Sphyrna tiburo | 2-5 feet long | These are the smallest type of hammerhead sharks. |
| Scoophead | Sphyrna media | 5-6 feet long | These sharks have a mallet-shaped head. |
| Winghead | Eusphyra blochii | 5 feet long | These sharks hunt at the bottom of the sea. |
| Scalloped Hammerhead | Sphyrna leweni | 6.5 feet long | Their head is arched and has seven notches in it like a scallop. |
| Scalloped Bonnethead | Sphyrna corona | 4.5 feet long | Young do not always reach adulthood due to overfishing. |
| Carolina Hammerhead | Sphyrna gilberti | 9.8-13.1 feet long | This is a newly discovered species. |
Hammerhead Shark Habitats
Hammerhead sharks can be found across the globe. They inhabit both coastal waters and deep, open oceans. Hammerhead sharks migrate great distances. One method that helps them do this is rolled swimming. This is when the shark swims on its side to conserve energy.
These sharks tend to prefer warm, tropical waters. One of their favorite prey — the stingray — can also be found in these waters. Although the different species of hammerheads can all be found in warm, temperate waters across the globe, their exact habitat locations vary slightly.
Hammerhead Shark Species and Their Most Prominent Locations
The table below shows you where each type of hammerhead shark is most likely found.
| Hammerhead Type | Prominent Location |
|---|---|
| Great Hammerhead | Pacific and Indian Ocean, Arabian Gulf, Mediterranean Sea |
| Smooth Hammerhead | Hawaii, California, and Canadian waters |
| Whitefin Hammerhead | Off the coast of Africa |
| Smalleye Hammerhead | East Coast of South America |
| Bonnethead | Shallow waters and shores of the Atlantic Ocean |
| Scoophead | East Pacific Ocean and Western Atlantic, California, Peru, and Brazil |
| Winghead | Pacific Gulf, Phillippines, China, and Australia |
| Scalloped Hammerhead | Indian Ocean, Red Sea, Tahiti, South Africa, and Australia |
| Scalloped Bonnethead | East Pacific of Mexico |
| Carolina Hammerhead | Western Atlantic Ocean |
Are Hammerhead Sharks Dangerous to Humans?
Although hammerhead shark attacks are not very common, you should still use caution when near these animals.
©iStock.com/abadonian
Despite some of them being large, these sharks are not usually harmful to humans. There have only been 17 attacks recorded globally, and none of them resulted in fatalities. These sharks also have much smaller mouths than some other shark species. However, these are still wild animals, and if provoked they will attack humans. When near these animals always exercise respect and caution.
Are Hammerhead Sharks Endangered?
The hammerhead shark population is declining. Their species are being affected by overfishing, as are many other ocean wildlife species. They are also hunted for their fins, which are used in soups and other dishes. Did you know that shark meat is even used in the process of making pet food? According to CU Boulder Today, “A study led by Virginia Tech showed the great hammerhead, scalloped hammerhead, and smooth hammerhead species declined by an average of 90 percent from 1980 to 2005.”
The photo featured at the top of this post is © iStock.com/Howard Chen
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