Most modern shark families had developed by about 100 million years ago. Most sharks boast five to 15 rows of teeth in each jaw. They replace teeth all their lives, with a larger tooth replacing the one that falls out. This explains the abundance of fossil shark teeth. That s slightly less than a human eats.
Some sharks can live one year without eating.
They can grow more than 45 feet long. The smallest shark is the spined pygmy shark, less than 10 inches long. The mako shark, the fastest, can swim at speeds of 22 mph. They can sense vibrations more than a mile away. And they have an extraordinary sense of smell.