Sophisticated senses and a streamlined body characterise your ‘typical’ shark.
Their teeth are designed to rip and tear, or crunch and grind. Their skin is like chain mail; flexible and smooth, while also providing protection against attack.
So what you see here is this long yellow whip like soft coral. So in the middle of this whip you can see that there is a cat shark egg case, which has been attached to the soft coral.
The tendrils at either end of the egg case have been wrapped tightly around the soft coral, holding it firmly for the whole gestation period for the shark.
So the egg cases have little slits called fissures in them at each end, and that enables water flow through them. And when the embryo starts to develop, you'll notice that they actually start to use their tail to help get the water flow through the egg case, helping to oxygenate the water inside the egg case.
When we see the underside of the embryo we can actually see the external gills coming out from where the gills normally are situated and also the spiracles are just behind the eyes.
This particular embryo will continue to develop until all of this yolk is absorbed, at which time it will hatch, and it will essentially be a miniature version of the adult, on its own in the marine environment.
Modern sharks, as we know, have an entirely cartilaginous skeleton, and cartilage is lightweight and highly flexible, like our ear - you know, you can bend it and It doesn't break. And that's the ability of sharks to have this lightweight, flexible skeleton for faster swimming speeds. It helps them be more buoyant in the water at less weight. Plus, of course, they have large oil-filled livers that that give them kind of neutrality in the in the water.
Sharks have evolved a number of special powers. I like to call them shark super powers. For example, sharks have an incredibly acute sense of smell or olfaction. You know, they can smell blood in the water from a long way away.
Another feature that you can see quite readily is this amazing pattern of pores. These are actually called ampullae of Lorenzini, which enables the animal to be able to detect vibrations and detect prey. So even at night time, where there's no visual aspect to what the shark is seeing, they can still detect and know exactly where prey is. And that means up close sharks can detect the electric fields from prey that they want to eat, like a fish buried below the surface of the sand, or if they're in a feeding frenzy and they're up close in murky water, they can use their electro reception to detect exactly where the prey is before they chomp onto it.
They have a very hard sclera or capsule that the eye sits in and they're able to rotate the eye backwards into the head, exposing that the back of the eyeball, that sclera, and it looks like the eyes are going white when they do that, and that's to protect their eyes from damage.
When you're biting into hard bodied prey or biting through bones of a seal or something, you run the risk of breaking your teeth off. If you weren't able to replace those on a fairly regular basis, you'd eventually run out of teeth and starve to death. So the teeth of sharks are continually being replaced. They're attached to connective tissues growing over the jaw of the sharks, and it grows outwards from a pocket in the back of the jaw and grows out and over the lip. And so the teeth are constantly rotating out of the mouth. The old worn, broken teeth drop off the front and the new sharp ones rotate up. It's often said that great whites have 300 teeth in their jaws, but only two rows in the upper and lower jaw of those are functional at any one time. The rest are all sitting back in these pockets waiting to rotate up into place.
They don't just rush up go [bite]. The first thing they do is get their bottom teeth in. Once they've got that, they drop down the top teeth. Then they have to shake their head like this. Because think of a wood saw: if you push a wood saw on a piece of wood, nothing happens. It's got to move. And their teeth are like the saw of a wood saw. That's why they shake their head when they're biting.
Making sense of senses
A shark’s unique sensory toolbox includes:
- An acute sense of smell, which works over long distances. Sharks can detect fish oil and injured prey up to several kms away
- A lateral line system detects vibrations and pressure changes up to about 100m away. A row of small pores runs from the snout to the tail. As water flows through these, sensory cells detect any pressure changes
- This lateral line also helps with navigation. As a shark swims, it makes waves that bounce off objects like rocks, letting it know what’s aroun
- Up close, electroreceptors pick up small electric fields radiating from creatures nearby. Found on the shark’s snout
Magnetic fields guide sharks
Sharks use Earth’s magnetic forces to navigate accurately over long distances. This is the conclusion reached by researchers from Florida State University.
When 20 Bonnethead Sharks (part of the Hammerhead family) were exposed to magnetic patterns that mimicked a home site about 500km from where they were captured, they turned to swim towards it. This ‘homeward orientation’ suggested the use of magnetic forces in navigation, said Bryan Keller, lead author of the study.
This may help explain how some sharks can travel across vast oceans but return to the same place to feed, breed and give birth.
Taking the direct route
In 2005, a White Shark was tracked swimming from South Africa to Australia and back again in almost a straight line. This led scientists to believe that sharks have a magnetic sense to guide themselves, similar to those found in sea birds, lobsters and turtles.
The denticles that cover a shark’s skin are flat, V-shaped scales. Small ridges line their surface. These channel water and reduce friction, helping sharks move easily and quietly through water. They also act as armour to protect sharks from predators.
This giant shark, which grows to 10m, has hundreds of tiny teeth, most of which aren’t used for eating. That’s because – like two other huge sharks, the Whale and Megamouth – the Basking Shark mostly feeds on plankton which don’t need chewing. It doesn’t really hunt for food, just swims along with its mouth open and eats whatever is filtered in by its gill rakers.
In case you’re wondering what this shark uses its many teeth for: hanging on during mating seems to be their function. The Basking Shark is commonly found worldwide in temperate and cool oceanic waters. The Basking Shark was targetted by fisheries in past years and is often involved in collisions with ships.
Status: Vulnerable. IUCN (International Union for Conservation of Nature)
The tooth of the matter
Many scientists believe that sharks’ teeth evolved from the denticles that cover their skin. Over millions of years, these ‘migrated’ into the mouth to form teeth. Whatever their origins, sharks’ teeth are as varied as the creatures themselves.
Sometimes they’re just as you’d imagine, like the big sharp teeth of the White Shark. Other times they’re surprising, like the tiny teeth in the mouth of the massive Whale Shark. Conveniently, sharks’ teeth are continuously replaced, which gets around the problem of broken or blunt ones.
Another feature that you can see quite readily is this amazing pattern of pores. These are actually called ampullae of Lorenzini, which enables the animal to be able to detect vibrations and detect prey.
Gold medal swimsuit
Modelled on hydrodynamic (drag-resistant) shark skin, a full-body 50 per cent polyurethane swimsuit was worn by American swimmer Michael Phelps when he won eight gold medals and broke seven world records at the 2008 Beijing Olympics.
Between 2008-2010, nearly 200 world records were broken by swimmers wearing similar swimsuits, which reduced drag and gave them increased buoyancy and speed. Since 2010, there has been a worldwide ban on wearing full-body high-tech suits during competitions.