Amazing Sharks:🦈Deep Sea Creatures, Sea Dinosaurs

The ancestors of modern sharks appeared in the oceans about 350 million years ago. The earth then looked completely different than it is now: the continents and oceans have not yet acquired our usual outlines. Ancient sharks swam where in our time they sow wheat and build cities. Therefore, the fossil remains of sharks are sometimes found thousands of kilometers from the sea. Paleontologists - scientists studying ancient forms - most often find shark teeth. Fossil shark teeth are striking in their size. The largest — 15 cm long and weighing 340 g — belonged to a monster, in whose mouth could fit a man who had risen to his full height, and it reached 13 meters in length!

After hundreds of millions of years, the descendants of ancient sharks, having overcome the thorny paths of evolution, continue to plow the seas and oceans. Sharks, of course, are in many ways inferior to bone fish that are more progressive in structure. Fishes Sharks do not have bones - their skeleton consists entirely of cartilage (although their ancestors had a bone skeleton). The gill slits of sharks are not covered by gill covers. And most importantly, sharks, like all cartilaginous fish, do not have a swimming bladder. In part, however, swimming shark bladder replace fat deposits in the liver.

To stay in the water and not sink to the bottom, the shark spends life in constant motion. She also does not have to sleep, only coastal and reef sharks allow themselves to relax at the bottom of underwater caves. The gills of sharks are not as perfect as those of bone fish. And they extract only half of the dissolved oxygen from the water (80% of bone). The shark must also move continuously so that its gills are constantly washed by fresh water. It is no coincidence that captive sharks become "sleepy" from a lack of oxygen. Sharks caught in the net often suffocate and die long before they are pulled out of the water. However, the ancients do not mean primitive.

The shark is perfectly adapted to life in the ocean. The body of the shark has a perfect streamlined shape. Triangular teeth are located in 5-6, and even 15 rows. The total number of teeth reaches several hundred, and each is sharper than a razor. The back teeth replace the front ones as they wear out, like cartridges in a revolver. For 10 years, a shark can blow up to 24 thousand teeth. Unlike most teeth, they grow in the skin, and do not grow to the bone. The compression force of the jaws reaches 18 tons! So even a medium-sized shark can easily bite a sea turtle or a dolphin in half.

The rough scales of sharks, scientifically called placoid, - the same teeth, only smaller, - resembles sandpaper. Sharks are very tenacious. There are frequent cases when a shark caught, gutted, and thrown back into the sea is again hooked. The most amazing "achievement" of sharks is their reproduction. Some sharks lay their "eggs" - eggs protected by a thick leathery shell equipped with "antennae" and allowing them to attach to underwater vegetation. But most sharks, not trusting the vagaries of fate, bear their offspring themselves and give birth to live cubs. A shark sees the world in a black and white image and enough "ear tight". But she has a very delicate sense of smell and a well-developed lateral line, which gives her a "sixth sense", allowing her to catch the smallest fluctuations in water.

Thanks to the lateral line organs, the shark can feel the movement of large fish at a distance of up to 300 meters. To top it all, the shark has one more organ on its head - the so-called Lorencini cells, with the help of which it senses changes in pressure, electromagnetic permeability and temperature. Everyone knows: sharks are predators. A shark attacks everything that seems to be possible prey: fish, turtles, seabirds and mammals, its fellow sharks, and once sharks attacked an elephant that entered the sea off the coast of Kenya.