They will wildly attack the food and anything in the area, even each other, sometimes wounding or eating fellow sharks. Scientists have shown that sharks are relatively intelligent and can learn at a rate similar to that of rats and birds. Some sharks live near the surface, some live deep in the water, and others live on or near the ocean floor. Some sharks even venture many miles up into the fresh water of rivers like the Mississippi in the USA and the Amazon in Brazil. Others, including the dogfish , Greenland , and goblin , live in cool waters.
Some sharks stay in the same region their entire lives while others travel across oceans.
Examples include the bonnethead shark, and the nurse shark . Examples include the dusky shark, the blacktip sharks , the tiger shark , and the sandbar shark. Highly pelagic sharks - these sharks migrate across oceans. Examples include the blue shark and the mako . They evolved over 100 million years before the dinosaurs did.