Most modern shark families had developed by about 100 million years ago. Sharks sink if they don't swim. Most sharks have 5 to 15 rows of teeth in each jaw. The teeth don't have roots and are easily broken off. A tooth usually lasts a week before it falls out.
Sharks keep replacing their teeth all their lives.
A larger tooth replaces a smaller one that falls out. A shark may lose thousands of teeth in its lifetime. This explains the abundance of fossil shark teeth. The Great White Shark appears to be a finicky eater with little taste for humans. In 78 attacks recorded along the California coast since 1926, there have been just 8 deaths.