Sharks predate dinosaurs – and these incredible fish have used their lengthy time on the planet to perfectly adapt to their surroundings. ZSL researcher Dr David Jacoby reveals a few things you never knew about these incredible creatures.
1. The earliest sharks date back to around 450 million years ago, meaning they were around millions of years before dinosaurs walked the Earth. Perhaps the most formidable extinct ancestor of modern-day sharks was the megalodon. An ancient version of the great white, it was around 20 metres long and weighed around 48 tonnes.
2. There are more than 500 species of shark, and just three (the great white shark, bull shark and tiger shark) are responsible for most reported attacks on humans. Such attacks are very rare – in fact, for every human killed by a shark, two million sharks are killed by humans, with a quarter of the world’s shark species now at risk of extinction. In fact, you’re 75 times more likely to be killed by lightning than by a shark.
3. Sharks get through up to 30,000 teeth in a lifetime. They never stop generating new teeth, and their gums work like a conveyor belt: teeth grow from the back and move forward when needed, so if a tooth breaks in the front row, there’s always a row behind to replace it. And they get through a lot!
4. The sea isn’t the only place sharks can be found, as a few species have the ability to venture into freshwater systems. In the Bahamas, South Africa and Australia, bull sharks will travel up and down rivers. It takes a lot of energy for them to move between saltwater and freshwater, but being able to do so opens up a whole new set of prey for them. Meanwhile, the epaulette shark, which is found around coral reefs in New Guinea and Australia, can leave the sea by climbing out of the water at low tide and ‘walking’ between tide pools to hunt stranded prey.
5. There are far more sharks off the UK coast than people think, including larger species such as blue sharks and basking sharks. They are most often spotted around England’s south-west coast, north of Ireland and Scotland. Sharks are found in all of the world’s major oceans, even in the Arctic, which is home to the Greenland shark. This remarkable fish is thought to live for up to 400 years, making it the longest-living vertebrate known to science.
6. Sharks can adopt some very unique – and clever – ways of hunting. Thresher sharks have an incredibly long upper caudal (tail) fin, which they use like a whip to stun and kill their prey. Angelsharks, on the other hand, are ambush predators. They bury themselves in sand and wait for prey to go over their heads, then pounce with their big, extendable mouths. Great white sharks have also been known to use the angle of the sun to hide their approach when hunting seals.
7. Some sharks have evolved in a way that means they have to keep swimming to breathe – the great white is one example. We don’t really understand how this impacts them sleeping, but there has been recent footage showing a female great white, where she minimises as many of her bodily functions as possible while still moving. It could be a similar system to dolphins, as they can shut down one side of the brain so just the other half is regulating them. As yet, no one knows for sure whether sharks are capable of this.
8. Tiny pores in the end of a shark’s snout are filled with a gel that is very sensitive to electrical signals in the water. This is known as an electrical sense, and makes up one of the shark’s three primary senses. They use those three senses at different times – to initially approach prey, they use smell, then the electrical signal is used for more fine-scale hunting, with vision kicking in at the last minute only.
9. There can be a huge variation in the size of different shark species – the largest alive today is the whale shark, a whopper that can grow up to 40 feet in length and weigh up to 4.5 tonnes. At the other end of the spectrum is the dwarf lantern shark, which can fit in the palm of your hand. These curious fish are found in very deep water, so few people ever see them.
10. Some shark species have been known to reproduce via a virgin birth – a process known as parthenogenesis. This was recently observed in the critically endangered smalltooth sawfish. It occurs when females fertilise themselves with material that splits off from an egg as it divides, but then fuses back with the egg. Some sharks have also been known to eat their siblings in the womb. The fastest-growing embryos will feast on the yolk sacs and embryos of their less developed brothers and sisters.
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