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550 million years ago, the  ocean was a simple ecosystem,  

full of reefs made by bacteria, and a gooey  mat of microbes that covered the ocean floor.  

Creatures were simple, often  amorphous. None were yet predatory.

But within a few million years, this simple  ecosystem would disappear, replaced by an ocean  

full of diverse, mobile, and highly effective  animals. The world's first predators emerged  

during the Cambrian explosion, 540 million years  ago, in the form of giant shrimp like creatures  

like, Anomalocaris, which trapped its prey in  its mouth lined with hooks, or the five-eyed  

Opabinia, which caught its victims using a  flexible clawed arm attached to its head.  

Soon, the first fish emerged - the jawless  Agnatha, of which two groups still survive today:  

the lampreys and the hagfish. And by 450 million  years ago, the ocean was populated by the ancestor  

of what is now the most fearsome  predator of the sea - sharks.

The first modern sharks arrived in the  late Devonian 370 million years ago,  

taking the iconic shape we know today. They  were six feet long, with a streamlined body,  

5-7 gill slits, and dorsal fins.

Soon, sharks dominated the oceans. The  Carboniferous Era was a period with some  

of the most unique sharks that ever existed.  Strange species like the Stethacanthus,  

a shark with what looks like an anvil on its head,  the Eugeneodontida, a shark with a tooth whorl at  

the end of its bottom jaw, and the Falcatus,  a shark with a long, sharp horn on its head.

But these strange iterations of the  shark have long since gone extinct.  

The sharks that prevailed were largely  streamlined, with a pointed snout,  

large pectoral and dorsal fins, and a strong  crescent-shaped tail, like the great whites or the  

shortfin mako. Sharks like these have dominated  the seas for hundreds of millions of years.

That is, until evolution decided to take a  strange turn. Around 20 million years ago  

evolution created the newest shark to enter  the water - arguably the strangest one of  

them all. With a mallet shaped head full of  sensory organs, and eyes set on either end,  

the hammerhead is one of the most recognizable  and downright bizarre looking animals on earth,  

their body plan a drastic departure  from the other sharks that roam the sea.

They are found in temperate and tropical  waters worldwide and can often be seen in  

massive numbers as they migrate to colder water.  6 meters long and weighing up to 450 kilograms,  

hammerheads are a formidable and  dominant force across the world's oceans.

Why only recently did shark evolution take such  a surprising turn, making something so different  

from the rest? And what does their odd-shaped head  do that gives hammerheads their evolutionary edge?

The iconic hammer of the hammerhead  shark is called a cephalofoil,  

and the size of it varies from species to  species. It's easy to assume this weird  

shape is a rubbery extension of flesh, but it  is actually a flattened and stretched out skull.

The smallest is the modest bonnethead, Sphyrna  tiburo, also known as the shovelhead. The largest  

is the winghead shark, Eusphyra blochii,  whose wing-like head is so big its width is  

nearly 50% of its total body length. All other  hammerheads fall between these two extremes.

And on the tip of all of the hammerhead's  cephalofoil are their weird beady eyes. This  

configuration is a little baffling.  Being as spread out as they are,  

it would seem like each eye would see the  world independently, with no overlap in  

each eye's vision - not something that  would be very helpful for a predator.

The visual field in all creatures is the expanse  of space visible to them without moving their  

eyes. In humans, our forward facing, horizontal  visual field is around 190-degrees. And our  

binocular vision, where the vision of each  eye overlaps, giving us depth perception,  

covers 120 horizontal degrees. In fact  most predators have large binocular fields,  

to help quickly scan the environment for prey,  an ability made possible by having eyes that face  

forward. By contrast, most prey animals  have eyes on the sides of the heads,  

to help them be aware of danger coming  from any direction. Pigeons, for example,  

have a visual field of around 310 degrees,  but a very narrow binocular portion in front. 

You can see this pattern throughout  the animal kingdom - prey and predator  

species distinguishable by eye position.  But when you look at a hammerhead shark,  

it's not immediately obvious what's going  on there. They are obviously predators,  

but it's eyes are far apart, and in a totally  unique configuration from all other vertebrates.

Does the weird shape of the  hammerhead hurt, or help their vision,  

and thus their predatory ability?

In 2009, researchers started to get to the  bottom of it. They compared the visual fields  

of three hammerhead shark species to two  sharks with a more typical head morphology,  

to see which type of shark body plan  offers a more enhanced binocular field.

All sharks in the study had a full 360 vertical  visual field, with similar vertical binocular  

overlaps. But when looking at the horizontal  visual field, the differences were profound.  

The total monocular visual fields ranged from 308 degrees to 340 degrees,  

with the hammerheads on the upper end. And  when comparing binocular field of view,  

the hammerheads were the clear winners. The lemon  shark had a mere 10 degrees of binocular overlap,  

the blacknose just 11. The modest  bonnethead had a bit more with 13,  

and the scalloped hammerhead had 32 degrees of  overlap. And the winghead shark, the one with the  

widest head, had 48 degrees of binocular overlap,  nearly four times that of the typical sharks.

It's clear then that the binocular overlaps in  

hammerheads increases as the  width of the head increases.

This gives them an advantage when hunting for  prey, by giving them exceptional depth perception.  

Out of all the sharks, they have the clearest  view of the underwater world, and it shows.  

Hammerheads are some of the most effective  predators among the sharks - easily  

catching and devouring stingrays,  octopuses, and even other sharks.

This alone may have been enough to influence  the evolution of the hammerhead cephalofoil.  

But the long, flat shape of the head does more  than give the shark better vision. It also  

gives the hammerhead unique hydrodynamics  found nowhere else in the animal kingdom.

When you think of agility and speed in the  ocean, you think of animals like mako sharks or  

bottlenose dolphins - animals with a streamlined,  pointed nose, that cuts through the water.

But a hammerhead shark is basically the opposite  of that. It's like an airplane with a wing  

attached to its front. Hammerheads have to use  much more energy than other, normal shark species  

just to swim because of the increased drag.  It's a lot of work to push that thing around.

So the obvious question is  - why would nature do this?  

What benefit does this give  to the hammerhead, if any?

Elasmobranchs, like sharks and  rays, don't have a swim bladder,  

so they have to constantly swim  to avoid sinking to the bottom.  

So for a long time, it was thought that  the cephalofoil indeed acts like a wing,  

producing lift forces that help the hammerhead  stay vertically positioned in the water column.

This theory seems to make sense, when you  compare the cephalofoil to an airplane wing.  

The hammerhead hammer looks just like  one - the structure's technical name,  

cephalofoil, even means “head  wing.”

It's easy to assume then  

that the flow of water over the cephalofoil  works just like the flow of air over a wing.

To test this theory, researchers laser  scanned the heads of 8 species of hammerhead.  

Each digitized head was then placed  in a virtual underwater environment,  

allowing them to measure  water pressure, drag and flow.  

They then did the same for a few shark  species with more typical pointy heads.

And surprisingly they found that the cephalofoil  does not create lift when the shark is swimming  

in a regular, forward motion. But when the  head is tilted up or down, strong forces  

quickly come into play. When the angle of attack  changes, the shark can rapidly ascend or descend.

The hammer is not for lift,  but for maneuverability.

And this type of motion is essential for how the  hammerhead hunts. Unlike mako sharks that chase  

down prey in long pursuits, hammerheads swim just  above the sand, looking for bottom dwelling prey.  

Once detected, these prey animals, like  stingrays or squid, will erratically dart  

away to try to escape, zig zagging up, down,  left, right. And the hammerhead follows suit.

Supporting this hypothesis is the winghead shark,  who has the biggest head of all the hammerheads  

compared to its body. It has the largest amount  of drag- but also shows the greatest change in  

lift as the attack angle changes. Of all the  hammerheads, it has the best maneuverability.

And when you look at its diet, you can see why  evolution would create something so extreme.  

Most hammerheads eat crabs or  stingrays - creatures that are quick,  

but not known for their sheer agility.

But the winghead diet consists of about 93%  

teleost fishes - like herrings -  which are very fast, and very agile.

The cephalofoil gives the hammerheads  an agility unmatched in the world  

of sharks - allowing them to fill an  ecological niche that other sharks cannot.  

But on top of this agility, hammerheads possess a  6th sense, something which we have no equivalent  

to - their ability to detect minute and  invisible electric fields in the water.

The underwater world for us is distorted - our  vision blurred, our hearing muffled. We can  

immediately tell that the ocean is not where  we belong. But on top of our senses becoming  

out of whack, there is so much more going on  under the waves than we could ever perceive,  

a world of stimuli that we can't pick  up on at all, a world of electricity.

Electroreception is a 6th sense  to many aquatic creatures.  

It's an ability to detect the electrical  fields that permeate the water,  

giving navigational cues and information about the  location of prey. In fact, it is observed almost  

exclusively in aquatic animals since water is a  much better conductor of electricity than air.

Many members of the elasmobranch  fish family share this trait,  

but sharks' electroreception  abilities are the most finely tuned.

Sharks receive tiny electrical  signals from their environment  

via a series of pores peppered over their heads. These pores are distributed in discrete patterns,  

varying somewhat among elasmobranch species.  In this picture of a great white shark,  

you can see the clusters of pores  around its eyes and nostrils.

These pores are filled with an electrically  conductive jelly, and lead to tiny bulbous cells,  

called ampullae of Lorenzini. And this is the  key to their amazing power. All animals generate  

electricity around them as their muscles  contract in movement and their heart beats,  

and this current radiates away from them in the  water. When these electrical currents travel  

towards the shark and through the jelly, they  stimulate cilia - hairlike projections on the  

ampullae, which then trigger the sensory neurons. This then triggers neurotransmitters in sharks'  

brains, which tells them they  are close to something alive.

This sense works even when the  conditions underwater render the five  

other common senses—sight, smell,  taste, touch, hearing—useless.  

It works in turbulent water, in total darkness  and even when prey are hidden beneath the sand.

And for the hammerheads, this  sense is even more extreme.

With a wider head, hammerheads have a greater  number of electrosensory pores. The pores are also  

located over a broader area, which increases the  surface area that the head can sample, and thus  

increases the probability of a prey encounter.  So when the hammerhead swims above the sand, it  

waves its head like a metal detector looking for  treasure - its treasure being a buried stingray.

And the sensitivity of this metal detector head  is profound. Researchers found that newborn  

Bonnethead Sharks can detect electric fields  less than 1 nanovolt per square centimetre.

This is around the equivalent to the  intensity of a voltage gradient that  

would be created in the sea by connecting one end  of a 1.5volt AA battery to the Long Island Sound,  

and the other end in the waters  off of Florida.Theoretically,  

a shark swimming between these places could  tell when the battery was switched on or off. 

Such incredible electrical sensitivity is over  five million times greater than anything we  

could ever feel. Even our best technology  struggles to detect something that minute.  

It is likely the most powerful  electrical sensing in the animal kingdom.

We often think of the weirdest, cartoon-iest  animals being things of the past. Creatures that  

were giant, strange, or sinister. But hammerheads  show us that evolution is never finished.  

What seems illogical, or even detrimental, to  an animal's survival can be the key to them  

fitting into a very specific environmental niche.  It's a fun thing to think about - what else will  

appear on earth in the next 50, 100 million years?  What will sharks look like given that much time?  

Some reef shark species have  recently evolved the ability to walk,  

even above the water at low tide. Other species  have recently been discovered to glow in the dark,  

others can live in freshwater in addition to  salt water. What else does the future hold  

for sharks like the hammerheads? It's hard to  speculate, but the possibilities are endless.

Sharks have dominated the seas since the  end-Cretaceous, and as a group, have survived  

all 5 mass extinctions so far, in large part due  to their ability to fill many varying ecological  

niches. But the hammerheads, as the newest species  of shark, have not yet faced such an event. That  

is, until now. Many believe we are currently  living through the 6th mass extinction due  

to human activity, and sharks, especially the  hammerheads, are among the most at risk. One  

study in Australia reported that 80% of scalloped  hammerheads have been lost. They are threatened  

by commercial fishing, mainly for the shark fin  trade - where the fins are cut off and the rest  

of the body discarded. Their numbers, like many  sharks, are dwindling, and if we, as a species,  

are not careful, we may never get to see what  the future holds for such incredible creatures.

Being able to talk about the  science and conservation subjects  

near and dear to my heart on a  platform with such a wide audience  

is something I once could only have dreamed  about. After finishing college I knew that  

science communication was my passion - I just  needed to find a way to make that my career.