Sharks belong to the class of Chondrichthyes (cartilaginous fish) and already inhabited the oceans of the world around 400 million years ago. Unlike bony fish, they have no spine and their skeleton is composed of hard cartilage. While sharks can be found all over the world, the majority of the 500 species known to us today are at home in tropical and subtropical waters. Some species, such as the Greenland shark (Somniosus microcephalus) or Ganges shark (Glyphis gangeticus), live in colder oceans or in freshwater and brackish water habitats. Bull sharks (Carcharhinus leucas) are able to live permanently in fresh water. They are found in regions including the Amazon and the Zambesi.
The whale shark (Rhincodon typus) is around 14 metres long and can weigh up to 12 tonnes, making it the largest living cartilaginous fish. The smallest sharks include the dwarf lantern shark (Etmopterus) which grows to a maximum length of 20 centimetres and a weight of only 150 grams.
Shortfin mako sharks (Isurus oxyrinchus) are among the fastest fish in the world, reaching speeds of around 90 kilometers per hour.
The record for the oldest shark currently known to man is held by the North Atlantic spiny dogfish (Squalus acanthias), which can live to the age of around 80. Sharks generally reach an average age of 30 to 50.
A unique feature of shark anatomy, the Ampullae of Lorenzini are found at the tip of the nose. These organs are electroreceptors which enable the shark to detect electrical impulses such as the heartbeats of other animals in the vicinity. However, sharks also have outstandingly developed senses of hearing, sight and smell.
Shark teeth are arranged in multiple consecutive rows. If a tooth in the front row breaks, a tooth from the next row moves forward and replaces the broken tooth within a few hours.