There are over 500 species of sharks, and together with skates and rays this group of fish are known as ‘Elasmobranchs’. They have cartilage skeletons and first evolved around 4 million years ago, before dinosaurs walked the lands!
While we have five senses, sharks and rays have seven.
- water pressure sensitivity, and
- electrical field detection. They can detect slight electrical fields produced by muscles (as tiny as 0.05 millionth of a volt).
Sharks do not have scales like most other fish. Their skin is made of tiny dermal denticles which function to streamline their bodies making them hydrodynamic. Under a microscope the denticles resembles small teeth-like structures.
Water temperature is one of the most important factors driving shark distribution. Most sharks are ectotherms (cold blooded) but some like the Great White shark can maintain a warmer body temperature than surrounding seawater. They can have a body temperature 10°C higher than the surrounding water.
This allows them to hunt fast prey in cold waters.
About 40% of sharks are egg laying, the rest are viviparous and give birth to live young either nourished by a yolk sac or a placental attachment. Great White sharks give live birth, but this has never been witnessed. They could give birth to an estimated six pups although this is one of those great unknowns. Pups are already 1.5m (5 foot) in length when born.