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Hammerhead in the Galapagos, she is near the surface with a wave breaking in the background.

Types of Hammerhead Sharks: The Details

There are 5 species of hammerhead shark found along the Eastern United States, S. lewini (Scalloped hammerhead), S. cf. S. media (Scoophead hammerhead), S. zygaena (smooth hammerhead), S. tiburo (Bonnethead), and the new species S. gilberti (Carolina hammerhead). Globally, there are 2 genera and, including the recently described Carolina hammerhead, at least 9 species of hammerhead sharks.

Hammerheads are probably the easiest sharks to identify due to their scalloped-shaped extensions of their heads. These extensions are sometimes called cephalofoil (Michael, p. 68). The shape of the cephalofoil changes slightly from juveniles to adults. However, in adults, the cephalofoil shape is consistent and varies from species to species. This makes identification of adults among species somewhat easy.

Probably one of the most common questions about hammerheads is "Why do hammerheads have a scalloped-shaped head?" No one is exactly sure. However, there are some unique advantages to having this peculiar head structure. The scalloped-shaped head spreads out the shark's senses, including its sight, smell, and electric field receptors. This enhances the shark's senses. The head may also aid in maneuverability, acting as a bow plane in the water (Michael, p. 68). Finally, hammerheads have been known to use their heads to bat and pin stingrays to the ocean bottom for easier feeding (Michael, p. 68).

Another distinctive feature of hammerheads is their large and tall dorsal fins, and elongated upper portion of the caudal (tail) fin. The unique scalloped head along with the diagnostic dorsal fin and tail make these sharks unmistakable in identification.

Unfortunately, most hammerhead sharks have been overfished. Their numbers have severely diminished over recent years.

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Select Hammerhead Species:

1: S. mokarran - The Great Hammerhead

The most well known hammerhead shark is S. mokarran, the Great hammerhead. The Great hammerhead shark has a nearly straight cephalofoil with an indentation at the center anterior margin. Specimen sizes of around 14 feet (425 cm) are common, and they may reach lengths of up to 20 feet (610 cm) (Castro, p. 155). These sharks are found world wide in tropical to semi-tropical waters, including the Atlantic from the coast of North Carolina to Florida and the Gulf of Mexico (Castro, p. 155).

The Great hammerhead preys heavily on rays, with other sharks, bony fishes, squid, and crustaceans in its diet (Michael, p. 69). Based on this varied diet, it is not surprising that some shark attacks on humans have been attributed to Great hammerheads. However, they are usually not aggressive toward divers (Michael, p. 69).

This shark has little commercial value, and is not directly targeted by commercial fisheries. However, it is often caught on fisheries' longlines and drift nets. Some countries use the shark for its fins. It is also classified as a game fish and loved by sports fisherman. The International Union for Conservation of Nature and Natural Resources (IUCN) has the Great hammerhead listed as data deficient. This means there is not enough data on the sharks' populations to make a conclusion about the status of this shark.

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2: S. lewini - The Scalloped Hammerhead

The Scalloped Hammerhead is the most common species of hammerhead shark. Like the name says, the cephalofoil has a scalloped shape. They are found nearly globally in warm temperate and tropical coastal waters. They can obtain sizes around 4 meters in length. Scalloped hammerheads are often found in large schools, as in the Galapagos examples in the next section.

These sharks mainly eat fish and are considered harmless to humans. Unfortunately, populations of Scalloped Hammerheads have greatly diminished over the years mainly due to overfishing.

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3: S. gilberti - The Carolina Hammerhead

This newly discovered shark species, found off the coast of South Carolina, was named in 2013. It is considered a cryptic species, as it looks identical to the Scalloped hammerhead shark. The only exception is that it has 10 less vertebra and is genetically different.

In 1967 Dr. Carter R. Gilbert reported a Scalloped hammerhead with 10 less vertebrae than normal. After this description in 1967, no other research occured until thing else happened until 2006, when J. M. Quattro, et al. (2006) were studying scalloped hammerheads and noticed the specimens had two different genetic signatures, indicating two separate species.

This second species, S. gilberti is much more rare than the original species, S. lewini. So, like the scalloped hammerhead, the populations of this hammerhead shark are also assumed to have severely diminished.
J. M. Quattro published a paper describing this specimen in 2013 (Link to the Paper).

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4: S. zygaena - The Smooth Hammerhead

The Smooth hammerhead has a cephalofoil that does not contain an indentation in the front center, and the sides have a hammer like shape. They can grow up to 5 meters in length and have a near global distribution in temperate waters. The Smooth hammerhead feeds on fish. It is one of the more common sharks in temperate waters and is unfortunately sought after for its fins for use in shark fin soup.

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5: S. media - The Scoophead Hammerhead

This is one of the smaller hammerhead shark species. Adults only grow up to 1.5 meters in length. The cephalofoil is distinctive and looks like a spade shovel. They are found in the Western Hemisphere in tropical waters of the western Atlantic (Near South America) and the eastern Pacific ocean (South America and Central America).

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6: S. tiburo - The Bonnethead Hammerhead

The Bonnethead is another very small hammerhead shark. It also grows to around 1.5 meters in length. It's range is similar to the Scoophead hammerhead, but extends further north into the Gulf of Mexico, Carribean, and East Coast of the United States. Along the Eastern Pacific, it's range extends into southern California. The small Bonnethead shark feeds on mainly crustaceans from the sea bottom.

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7: Eusphyra Blochii - The Winghead Hammerhead

E. blochii is the only hammerhead in this genus. It has an extreme cephalofoil; it is very long and slender, which looks like airplane wings. The Winghead is a somewhat smaller and slender hammerhead that can reach sizes of around 1.8 meters. The Winghead inhabits tropical waters from the coastal areas of the Indian Ocean to northern Australia.

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Images - Diving with Hammerhead Sharks in the Galapagos Islands

The Galapagos islands are famously known for Darwin and the amazing endemic land fauna. However, because of severe fishing restrictions around these remote islands, the waters around the Galapagos are completely undisturbed. These waters have become one of the worlds premier dive sites to see large pelagic fauna, specifically sharks and rays.

I was fortunate enough to dive in the Galapagos Islands and experience the fauna first hand. Amung the many large fish, rays, and sea turtles, were Scalloped hammerhead sharks. Around Wolf islands and Darwin Arch, these dosile sharks school in the 100's. This should truly be on the bucketlist for anyone interested in these beautiful creatures.

Below are some images of ~10 foot Scalloped Hammerhead sharks I routinely dove with. I borrowed a dive buddys camera for a few dives and snapped these shots.

Click on an image to see it full sized.

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High Quality Shark Teeth by Fossilera

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The Teeth of Hammerhead Sharks

Hammerhead shark teeth have smooth cutting edges, and have a distinct notch on the distal side separating the crown and enameloid shoulder. This is often referred to as a "hammerhead notch" (Cocke, p.76). Their distal enameloid shoulder is another distinguishing characteristic. This shoulder is convex and often not serrated. Larger Sphyrna teeth can have week serrations on this shoulder. Hammerhead teeth also have a deep nutrient groove. All of these characteristics can be seen in the image below which shows a lingual and labial view of a hammerhead tooth. As for size, their teeth usually range from 1/4" to around 3/4" (6 mm to 19mm).

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Similar Shark Teeth

Hammerhead teeth can be confused with gray shark teeth, especially worn gray shark teeth. They can also be confused with a smaller genus of shark, Rhizoprionodon sp., the sharpnose sharks. The image below shows a comparison between a worn hammerhead (Sphyrna sp.) tooth, a worn lower Carcharhinus sp. tooth, and a Rhizoprionodon sp tooth.

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Fossil Hammerhead Shark Teeth: Where to find Hammerhead Shark Teeth

Fossil hammerhead shark teeth are found in any marine Miocene and Pliocene deposits. These include deposits along the entire east coast of the United States. However, they are less common than many other shark species. Also, due to their relatively small size, they are often overlooked. Refer to the identification images above when fossil collecting, so you don't confuse them with similar species of fossil sharks.

Places to find them include the Chesapeake Bay Area (Calvert Cliffs Site), North Carolina (Aurora Site), and Florida (Venice Site).

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Fossil Examples:

Sphyrna zygaena aka laevissimus: Hammerhead Shark
The Common Hammerhead (Sphyrna zygaena) still populates the Chesapeake bay today and is one of the largest sharks in the bay.

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Sphyrna sp.(Rafinesque, 1810): Hammerhead Shark
There are three species of Hammerhead found at Aurora, S. lewini (Scalloped Hammerhead) , S. cf. S. media (Scoophead), and S. zygaena (Smooth Hammerhead).

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Castro, Jose L. (1996). Sharks of North American Waters. College Station: Texas AandM University Press.

Hamlett, William C, ed. (1999). Sharks, skates, and rays : the biology of elasmobranch fishes. Baltimore : Johns Hopkins University Press.

Michael, Scott W. (1993). Reef sharks and rays of the world : a guide to their identification, behavior, and ecology. Monterey, CA.: Sea Challengers.

Purdy, R., Schneider, V., Appelgate, S., McLellan, J., Meyer, R. & Slaughter, R. (2001). The Neogene Sharks, Rays, and Bony Fishes from Lee Creek Mine, Aurora, North Carolina. In: Geology and Paleontology of the Lee Creek Mine, North Carolina, III. C. E. Ray & D. J. Bohaska eds. Smithsonian Contributions to Paleobiology, No 90. Smithsonian Institution Press, Washington D.C. pp. 71-202.

Quattro J.M. et al. (2013). Sphyrna gilberti sp. nov., a new hammerhead shark (Carcharhiniformes, Sphyrnidae) from the western Atlantic Ocean. Zootaxa, vol. 3702, no. 2; doi: 10.11646/zootaxa.3702.2.5

Quattro J.M. et al. (2006). Genetic evidence of cryptic speciation within hammerhead sharks (Genus Sphyrna). Marine Biology, March 2006, Volume 148, Issue 5, pp 1143-1155.