Many films and TV shows will tell you that sharks are scary and often eat beach–goers. Sharks play an important ecological role in the ocean.
Many of these fish are top predators (捕食者). They can help control populations of other animals. However, other sharks serve as clean- up crews, chowing down on migrating (迁徙的) birds when they fall out of the sky. Migrating land-based birds that fall from the sky as they cross the Gulf of Mexico can end up in the belly of a young tiger shark. But not all sharks are meat-eaters.
As a group, sharks are much, much older than we are. The first shark— like fish appeared more than 400 million years ago. Some have saw— toothed noses, and some may have big hooks on their heads.
They have super-sensitive noses and use snouts (鼻子) to find weak electrical signals from their food. Scientists are even trying to design materials to imitate shark's bacteria-battling skin.
A. But that's simply not true.
B. There are many different birds.
C. Sharks also have a lot of fascinating talents.
D. They usually migrate in a very long distance.
E. Some are peaceful plant- eaters, like the whale shark.
F. Since that time, they've existed in many different forms.
G. Tiger sharks, for example, eat migratory birds that fall out of the sky.
