The first half of this sentence is correct. Shark's teeth are not permanent, because sharks will change thousands of teeth in their lifetime. If only humans had such a function. But sharks do not have a fixed row of teeth, but five or six rows.

When the outer row of teeth falls off, the inner row of teeth will move forward to replace the original teeth. That is to say, the back rows of teeth are spare and substitutes. Sharks need to bite their prey, which requires a lot of teeth, so they have evolved such super functions.

Characteristics of shark teeth:

Shark's teeth are not fixed in a row like other animals in the ocean, but there are 5-6 rows. Except for the outermost row of teeth, the other rows are "supine", just like tiles on the roof.

Once the outermost tooth falls off, the inner row of teeth will move forward immediately to make up for the cavity position that replaces the fallen tooth.

At the same time, the larger teeth of sharks will constantly replace the smaller teeth during their growth. So sharks often have to change tens of thousands of teeth in their lifetime. According to statistics, a shark needs to replace more than 20,000 teeth in 10 years. There are more than 340 kinds of sharks in the world.

Sharks appeared 350 million years ago, but they kept all the features of prehistoric animals, such as soft bones and many cheeks on both sides of the jaw. In the deep sea, the average adult great white shark can reach 7-8 meters in length, and some can reach 12 meters, which is equivalent to the length of a bus. The biting force of great white sharks is 300 times that of humans, and they can easily bite their prey in half.