Bigeye thresher shark
Japanese horn shark
Spotted bamboo shark
Sharks possess the same senses of the man, more
other two to us strangers, that are the ability to perceive the electric
fields and the waves of pressure spreaded in water.
Sharks teeth are the most known part of these fishes, they constitute further a present element in the descriptions and in the images that have to strike our imagination. The teeth are similar to the placoid scales that dress the shark body; they are modified and of greater dimensions, not anchored to the cartilage of the jaws, but simply fixed in the derma by fibers of connective fabric. They are externally dressed again by an enamel that is very hard and resistant for the almost total absence of organic substance. The enamel protects a layer of dentina inside which the pulp is found, rich of blood vases. In the sharks jaws the teeth are prepared in more file, six and the last toward the inside of the mouth are generally tilted, covered by a fold of fabric and not yet completely developed. During the growth the tooth is subject to a move in ahead for the continuous formation of the gengival fabric to which is connected. In their advancement they progressively straighten, because of the simple mechanical tension, until they don't become entirely functional. After a few times the teeth of the anterior lines are destined to fall, following traumatic breakups or spontaneously and the biologist think they are singly replaced every 8-15 days, more frequently in the youngest samples. The biologist think that some kinds of sharks renew a whole line of teeth to the time.
characters the teeth of the sharks have forms and very different
dimensions, due to the alimentary habits of every kind, even if the preys
are almost swallowed without mastication. They can be long and pointed,
sharp, wide, of triangular form and with serrated edges: each of these
solutions is proper to a particular type of prey. The teeth of the
superior jaw are often different from those of the inferior jaw, to be
able to make the most effective bite. Generally the superior teeth, direct
to shear the preys, are greater, while those inferior, that have to
furnish the maximum taking, are thinner and pointed. For the different
forms and dimensions the teeth are held useful elements to the recognition
of the kinds and in some cases even of the sex. Some experiments have been
realized for appraising the strength engraved by the bite of a
Carcharhinus: it results of around 3 tons for square centimeter and the
sturdiness of the teeth has been compared to that of steel.
Many aspects of the sharks biology and ethology are not very well known, above all because of the difficulty to study these fishes in their natural environment and for their bashful and solitary behavior.. Here you will find some questions on the life of the sharks that don't have had answered ..
It seem that the pressure practiced by the bite of a shark Carcharhinus obscurus of around two meters is three tons for square centimeter! To that value could arrive then that of a white shark of the length of seven meters?!
According to Walter Starck the strips coloration white and
black horizontal, that reproduces that poisonous snakes of sea can be used
as anti-shark protection in the cases in which it is had to be to narrow
contact with these animals (es: taken back video, search, etc.).
The shark Carcharhinus longimanus is usual to follow the Globicephala macrorhyncus that swims and moves in numerous flocks. The delfinidis, because of the great dimensions, don't come certain considered preys from these sharks.. Which is the explanation of this behavior, really very particular??
The hammer shark Sphyrna lewini, normally solitary, has been observed to swim, in the reefs of Sanganeb in Red Sea, in numerous flocks, with the adult samples to the outside and the young people to the center.. Surely these sharks don't have to unite themselves in flocks to avoid the raiders, and probably they don't even do it for reproductive motives.. Which is therefore the explanation??
In the website www.prionace.it you can continue to read all the informations about sharks biology and etology, with images, video, news, and more about these marvellous animals..