The surfer said he believed he was bitten by a 6- to 8-foot-long great white shark, which sunk its teeth into his leg 10 times.
An extinction event about 19 million years ago decimated shark populations by up to 90%, researchers say.
The great white shark population off the California coastline is rising, per a study published in Biological Conservation.
According to Florida Fish and Wildlife, tiger sharks are second only to the great white shark in the number of bites on humans worldwide.
A Minnesota boy vacationing in Florida with his family survived a shark attack Sunday in Miami Beach.