NOT ONLY ARE SHARKS EXTREMELY IMPORTANT; THEY ARE ALSO FASCINATING AND SERIOUSLY COOL....
We have had sharks in the oceans for over 450 million years, and they have survived all five of the mass extinction events that have occurred during this time, some of which wiped over 95% of all species off the face of the earth! To put this into some perspective; Dinosaurs appeared around 230 million years ago, and subsequently became extinct in one of these events, and Hominids (Human-type animals) evolved 4.5 million years ago.
So not only have sharks been around 100 times longer than us, they massively outlived the Dinosaurs and even existed before the evolution of land plants and trees! In fact we even share a common ancestry with sharks; Our evolution from the oceans means that we have developed certain characteristics that originated in sharks and fish, our jaws and the muscles surrounding it that enable us to speak and chew, as well as small bones in our ears that enable us to hear, all evolved from the primitive gill arches in fish, and our top lip, jaw and palate all start life as gill-like structures on our necks in the womb.
Over this long period sharks have evolved to become the perfect predators within their environments, with species occupying almost every marine ecosystem including some in freshwater.
Although they can differ dramatically in appearance and size, (the smallest shark is the Pigmy Lantern shark 8.3 inches - to the biggest, the Whale shark 17 meters) all sharks share a few essential biological traits. For example sharks do not have a single bone in their bodies; their skeleton is made from cartilage, and they all share similar sensory organs. There are currently over 500 known species of shark, 600 species of skate and ray and 30 Chimaera - all of which belong to the class Chonrichthyans (cartilaginous fishes).
When you picture a shark often the first thing that jumps into your mind is the image of teeth, and lots of them!
Most shark species have between 5-15 rows of teeth and in fact you can really see the difference between shark species when you look at the design of their teeth, each species; depending on the environment they inhabit and the type of prey they consume has a tooth specifically designed for the job. These are very distinct, for example Great White sharks have large triangular teeth with serrated edges for tearing large chunks of flesh, where as Mako sharks have very pointed teeth for piercing and trapping fish.
The skin of a shark is covered with tiny teeth called dermal denticles (or placoid scales) These are covered in hard enamel and as the shark grows these fall out and are replaced with new ones. They function defensively to protect the shark but also reduce drag making the shark more efficient as it travels in the water. What is fascinating about these scales is that many scientists believe the teeth of a shark evolved directly from them....as sharks teeth are similar in composition and shape, and like the scales fall out to be replaced on a conveyer-belt type system.
Sharks have highly developed senses - in fact they have SEVEN of them! thats two more than we have. Not only this, but the senses that we do have in common are far more developed. Sharks possess a reflective layer behind their retina called a Apetum Lucidium which allows them to see in dark environments, meaning that their eyes are ten times more sensitive to light than ours.
Two thirds of the total weight of a sharks brain is made up of olfactory lobes, which allow it to analyse smell directionally; they can detect one part of blood to one million parts of water, equivalent to one teaspoon of blood in a swimming pool. Sharks also have very acute hearing and are particularly sensitive to the low frequency sounds associated with wounded prey or sporadic swimming. Their sense of touch is heightened by the fact that sharks have multiple nerve endings beneath their denticles and in their teeth which they use to identify objects with 'test' bites.
However it is the two extra senses that a shark possess which are by far the most impressive. Sharks are able to detect changes in water pressure through a system of fluid filled canals that run down the side of a sharks body - known as the Lateral line. Any variations in the water around the shark are detected through ripples in the water made by displacement or pressure; they can quite literally sense the presence of other fish around them.
Finally (and most interestingly) sharks are able to detect electrical currents! They have an extraordinary electrosensory system, comprising of jelly-filled pores on the snout and head called the Ampullae of Lorenzini which enable the shark to detect changes in the Earths geomagnetic field or the electrical currents given off by all living things such as a muscle movement or a heartbeat