1# The first sharks lived more than 400 million years ago—200 million years before the first dinosaurs. They have changed very little over the eons.
2# In its lifetime, a shark can have up to 30,000 teeth . They are continuously being replaced and shifted within the mouth.
3# Sharks are hypersensitive to pressure changes in the water. They can notice the slightest changes via specialized cells with tiny hairs in them.
4# A shark’s skin is tough and thick because it is made of a protein called collagen. The whale shark’s skin can be up to 10 centimeters thick.
5# While blood likely does not provoke a shark to attack, a shark in the vicinity likely can detect the blood. Without any conclusive proof of how sharks might respond, some scientists suggest women stay out of the water while menstruating.
6#Sharks have a highly evolved sense of hearing, which allows them to hear low-frequency sounds from up to quarter-mile away.
7# Young sharks spend seven years in a shallow water “nursery” where they grow and learn.
8# Sharks do not have a single bone in their bodies.
9# Unlike fish, sharks do not have a swim bladder to keep them afloat—for this, sharks instead have a large oil-filled liver. Sharks that spend a lot of time on the surface, such as whale and basking sharks, have a massive liver.
10# A bull shark can live in both salt and fresh water by regulating salt and other substances in its blood. A bull shark may have been responsible for a 1916 shark attack that happened in a creek in New Jersey. They have also been found in the Mississippi River