New discovery about hammerhead sharks stuns scientists

Scientists took DNA from eight of the nine species of hammerhead sharks and used it to look at their relationships. The results stunned them.

Hammerhead sharks are a strange looking species. They look like someone grabbed their skulls at the eye sockets and stretched them out to the sides, while the rest of their bodies look like those of a normal shark.

You might be wondering – what are the advantages of having a hammerhead ? And how did the hammerhead shark get its 'sea ranger' look ?

Gavin Naylor is a scientist who has studied sharks for nearly 30 years. The answers to some of these questions surprised even Gavin Naylor.

Hammerhead sharks are strange looking creatures.

Benefits of hammer

Scientists believe that hammerhead sharks have three main advantages.

The first has to do with vision . For example, if your eyes are facing opposite directions, such as towards your ears, you will have a much wider field of vision. Each eye will see a different part of the world, so you will have a better sense of what is around you. But it will be difficult to know how far apart things are.

Second , to make up for that trade-off, hammerhead sharks have special sensory organs, called canals of Lorenzini , scattered across the underside of their hammers. These pore-like organs can detect electrical charges.

The holes essentially act like a metal detector, sensing and locating prey buried in the sand at the bottom of the ocean. Sharks also have these sensory organs, but hammerheads have more of them. The farther apart these sensory organs are on the hammerhead's outstretched head, the more accurately they can locate food.

And finally , scientists think that hammerheads help sharks turn faster when swimming. If you've ever walked in a strong wind with an umbrella or flown in an airplane, you know how powerful large surfaces can be. If you're a hammerhead shark and your intended dinner is passing by very quickly, you can turn your head to catch it faster than other fish can.

Hammerhead shark family tree

It would be great if we could look at fossils and track the evolution of hammerhead sharks over time. Unfortunately, the fossil remains of hammerhead sharks are almost entirely made up of their teeth. That's because sharks don't have bones in their bodies. Instead, they're made of cartilage, which is the same as our ears and noses. Cartilage breaks down much faster than teeth or bones, so it rarely fossilizes. And fossilized teeth don't tell us anything about the evolution of hammerhead skulls.

Nine different species of hammerhead sharks swim in the oceans today. They vary in both the size and shape of their heads. Some have very wide heads compared to their bodies. These include the winghead shark (E. blochii), the great hammerhead shark (S. mokarran), the smooth hammerhead shark (S. zygaena), the scalloped hammerhead shark (S. lewini), and the Carolina hammerhead shark (S. gilberti).

Other species have hammers that are smaller in proportion to their bodies, including the bonnethead shark (S. tiburo), spoonhead shark (S. media), smalleye hammerhead shark (S. tudes), and scalloped scalloped scalloped shark (S. corona).

Scientists have long thought that the first hammerhead sharks didn't have hammers in the true sense, but that over time some shark species gradually evolved larger hammers. We think that the different hammerhead sharks alive today are snapshots from different periods in evolution – with the small hammerhead shark being the oldest in the family tree and the giant hammerhead shark being the most recent.

Since we don't have fossils to look at, scientists have explored this idea using DNA . DNA is the genetic material found in cells that carries information about the shape and function of a living thing. It can also be used to see how living things are related.

Scientists took the DNA of eight of the nine species of hammerhead sharks and used it to see how they were related. The results were not what we expected. It turns out that the older species have larger hammers, while the newer species have smaller hammers.

Where will the hammer evolve?

Older species have larger hammers, while newer species have smaller hammers.

When scientists think about evolution, we often think of living things changing little by little, gradually adapting to better take advantage of their environment. This process is called natural selection . But it doesn't always work that way, as the evolution of hammerhead sharks shows.

Sometimes an animal can be born with a genetic defect that turns out to be actually helpful to its survival . As long as the abnormality can survive and the animal can mate, the trait can be passed on. Gavin Naylor thinks that's exactly what happened with hammerhead sharks.

The earliest hammerhead to branch off was the winghead shark (E. blochii), which has one of the widest heads. Over time, natural selection has actually shrunk the size of the hammer. It turns out that the most recent hammerhead shark is the cap shark (S. tiburo), which has the smallest hammer of all.

Hammerhead shark is the common name for fish species of the family Sphyrnidae , order Carcharhiniformes in the subclass Elasmobranchii, class Cartilaginous fish.

The distinguishing feature of these fish is the special cartilage structure at the head that is flattened and extends to the sides to form the shape of a "hammer" called "cephalofoil". Hammerhead sharks belong to two genera, Eusphyra and Sphyrna, of which most species are classified in the genus Sphyrna, while the genus Eusphyra has only one species, the rake shark (Eusphyra blochii).

The hammerhead shark's habitat is warm coastal waters and continental shelves, most commonly found in the waters of Malpelo Island (Colombia), Cocos Island (Costa Rica), the Hawaiian Islands (USA), and South and East Africa.

Hammerhead sharks breed only once a year. The male will bite the female until she agrees to mate. Each spawning, hammerhead sharks give birth to about 12-15 young (the unslotted hammerhead shark can give birth to 20-40). The young sharks do not receive parental care and must swim together toward warmer waters to stay there until they are large enough to hunt on their own.

Hammerheads feed on fish, squid, octopus, crustaceans, and even their own relatives like Stingrays. Their unique head is used as a weapon when hunting. The hammerhead uses its head to incapacitate the stingray, weakening it. There is a larger and more aggressive species of hammerhead called the untracked hammerhead. This species is omnivorous, including all squid and octopus, and can be cannibalistic (other hammerheads and their own young).

According to the International Shark Attack File, humans have been the subject of 17 recorded unprovoked attacks by hammerhead sharks of the genus Sphyrna since 1580 AD. There have been no recorded human fatalities.

The great hammerhead and scalloped hammerhead are listed as endangered on the 2008 IUCN Red List, while the smalleye hammerhead is listed as vulnerable. The status given to these sharks is a result of overfishing and demand for their fins, an expensive delicacy.