File: Shark Trophy Animals in digital format

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Sharks, squales or selachimorphs are a super order of cartilaginous fishes, with five to seven gill slits on the sides of the head and pectoral fins that are not fused to the head. They are found in all the world's oceans and in some large rivers. Modern sharks are classified in the Selachimorpha or Selachii clade and are the sister group to rays. However, the term "shark" in a broad sense also refers to extinct species of the subclass Elasmobranchii, such as Cladoselache and Xenacanthus. The first sharks appeared in the Devonian, about 420 Ma ago. From the Cretaceous, 100 Ma ago, many shark species adopted their modern form. Since then, there are more than 500 species of sharks grouped in 35 families, not including ray species, which are now considered as sharks in their own right. Some species are only known from their fossils. Their size varies from only 14 cm in length for Etmopterus perryi, to more than 20 m for the Whale Shark. Despite its size, the latter feeds mainly on plankton by filtering the sea water. But most sharks are predators, even superpredators. Sharks are found in all seas, down to a depth of about 2,500 meters. They generally do not live in freshwater, but there are a few exceptions, such as the Bulldog shark and river sharks that can live in both salt and fresh water. They breathe through five to seven gill slits. Sharks have a coating of dermal denticles that protect the skin from parasites in addition to improving their hydrodynamics. They also have several rows of teeth that are renewed regularly. Despite a bad reputation conveyed by the media, only five species are considered dangerous to humans. According to the IUCN, one third of shark species are threatened with extinction (overfishing, bycatch, wanton disposal, etc.). They are used by humans for many purposes, such as food, leather goods, tourism, cosmetics and are sometimes kept in captivity. As superpredators, sharks are essential to their ecosystems. Global protection of sharks remains low, but some states are turning their territorial waters into shark sanctuaries.