Ancient, but awesome adapted to their world, endowed with amazing physical capabilities and special senses, even with an intelligence that makes you think, sharks are - and last - a hundred million years on Earth. Although associated in the collective mind, the danger, attack, bloody events, they are much more than that, and this limited vision, superficial, over them, shows how little is actually known.

1 . Sharks are called, generally, cartilaginous fish with elongated body, with hydrodynamic shape. Within its current classifications be supraorderl Selachimorpha or in a subdivision called Selachii (yes, I know, it's complicated - it's taxonomy, classification discipline dealing with living things). We don't want to complicate things, so we'll simply call them sharks.

Hydrodynamic form does not necessarily show like all the sharks from cartoons, with a pointed snout full of teeth. Evolution has endowed different species with different figures, sometimes presenting some lateral development in one region or another body but a close look, at least the back of the copula has the appearance typical of sharks - elongated and muscular.

2 . The oldest known fossils show that these animals appeared at least 420 million years ago.

3 . There are currently over 400 species of sharks, common in all oceans worldwide.

4 . The smallest shark is known far-lantern shark (Etmopterus Perry) found in the waters of Colombia and Venezuela. Mature specimens reach only 17 cm long.

5 . The largest is the whale shark (Rhincodon typus) which exceed 12 meters long and 20 tons weight. (No, do not eat people, is a huge peaceful - well, in terms of man - it feeds on plankton, small fish and squid.)

6 . Closest relatives of sharks as a group are sea cats, sea foxes & comp., which are all cartilaginous skeleton fish, but have a more developed body and flattened dorsal-ventral side, like a flattened shark. The group is called Batoidea, hence the name sometimes given to these creatures batoizi sharks. But the group descended from sharks Batoidea not "elongated", as long believed, but has developed parallel with them, from a common ancestor with theirs.

7 . Most shark species are marine. There are very few exceptions (the more remarkable), species that can live in saltwater and freshwater. Bull shark (Carcharhinus leucas) and river sharks (several species of the genus Glyphis, very little known) are not only living in brackish water estuaries (the mouth of rivers to the ocean), but also ascends rivers, in freshwater . Bull shark, one of the most dangerous to humans, after that lives in all ocean areas, and it works and upstream rivers in North and South America, Asia and Australia, sometimes thousands of miles way. Bull sharks have been found that climbed the Amazon to Peru, to Iquitos, a town located at 4,000 km of ocean.
Bull shark can also travel through a rare capacity, which is to change its internal environment, in terms of chemical composition, adapting it to the external environment characteristics. Thus, ocean, shark blood is kind of "focused" as very salty water around - has a high concentration of substances such as urea and trimethylamine oxide. But, when in fresh water, the animal must "dilute" the blood somewhat, and to decrease the concentration of urea, otherwise too much difference between the osmotic parameters of blood and those of fresh water would have fatal effects on the body. Bull shark manages to adapt to making and kidneys excrete large amounts of urea, blood osmotic adjusting such features to suit the surrounding environment.

8 . Shark skeleton is made not of bones but of cartilage. Cartilage, although it has only half the density of bone tissue, is more flexible and durable.

9 . Reproduction in sharks has many interesting features, since he's a fish. For example, unlike bony fish, sharks fertilization is internal and involves coupling the two partners of different sexes. Sharks have two male copulation organs, called pterigopode, they use (no, not both at once!) to transfer sperm to the female body (which has only one genital opening, to be completely clear). Again unlike most bony fish (who make a large number of eggs), sharks produce few offspring, but well developed.

Some sharks are oviparous, means eggs deposited in water, after a few days, offsprings will hatch. Eggs of these sharks have a shell leather with different forms and sizes of the species to another. Empty shells of the eggs sometimes reach the shore, the waves being taken on the beach, through some parts of the world, people call them "purses of mermaids".

Other sharks are ovoviviparous, meaning that the eggs hatch the female body even after growth for several months, and cubs are expelled soon thereafter.

There is also a third scenario: viviparous. Viviparous species of sharks, chickens develop in the mother's body, is directly related to it, the placenta-like organ found in mammals. They are therefore species' chicks born alive "as they say in familiar language.

And finally, are known cases (very few, but well documented) by parthenogenesis - asexual reproduction: female shark gave birth to baby without having had any contact with males, and genetic analyzes have shown that babies did not have DNA of paternal origin. This phenomenon was observed in captivity, probably, under normal conditions it is not very widespread, because asexual reproduction reduces genetic diversity, thereby decreasing the power of adaptation of the species.

10 . Sharks senses are among the most amazing adaptations and their explain in part their greater spread and diversity, signs of a remarkable evolutionary success.

Sense of smell is well developed, some species can distinguish blood in the water at concentrations of only one part per million.

Sight, especially important for predatory species, has nothing to do with colors, but rather the contrast between prey and background of those designs. Some sharks are well equipped for the night.

Hearing has a specific anatomical feature - on both sides of the body, inner ear is directly related to the outside through a hole - a feature which no bone or the fish to tetrapods (amphibians, reptiles, birds, mammals).

And besides these senses ... common, say (we're used to them because we have and new), sharks have some unique and fascinating sensory capabilities, associated with its special senses.

For example, they may perceive electromagnetic fields using electro receptor organs, called ampulele Lorenzini. As all creatures produce electrical signals (usually weak and can be detected only with special equipment), sharks use this sense to detect the presence of living creatures, potential food or potential enemies. Some scientists believe that sharks use the same common sense to guide the field lines following the land.

Lateral line organ is a typical fish, which they feel the vibrations transmitted through water, which can signal the presence of a living being that moves nearby. Sharks perceive vibration frequency between 25 and 50 Hz. Some experts believe that the lateral line contains receptors magnetic field as ampulele Lorenzini, filling their function.

Either way, it's certain that sharks pursue and capture their prey with great efficiency and are capable of long trips, some wander oceans, crossing thousands of miles each year, orienting themselves only they know how.

See below some species of shark.


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