1. Shark embryos attack each other.
Sharks are so tough, their embryos are known to attack one another. The largest embryo in a shark litter is known to eat its fellow embryos, in an act known as intrauterine cannibalism. Researchers looked at this phenomenon in sand sharks, noting that, "While 12 littermates may start the journey, all but one is eaten by the biggest in the pack. That strategy allows sand tiger sharks to have much larger babies at birth than other shark species, making the little ones relatively safe from other predators."
2.Sharks have a sixth sense.
In addition to their killer sense of smell, sharks also can detect prey by tapping into the small electrical fields that other animals generate using tiny organs called the ampullae of Lorenzini. These small pores, located near their nostrils, around the head, and beneath their snout, are something of second sight. The pores connect to long, jelly-filled bulbs that connect to nerves below their skill.
3. And it's strongest in hammerheads.
Hammerhead sharks have that funny-looking head for a reason. It contains a whopping 3,000 ampullary pores for picking up on electrical fields in the ocean. As MNN reports, "The hammerhead's increased ampullae sensitivity helps it track down its favorite meal, stingrays, which are usually hidden under the sand."
4. Hammerheads also have 360-degree vision.
Another advantage of hammerheads' weird heads is that they have incredible vision. A 2009 study found that the placement of their eyes gives them impressive binocular vision and the ability to see 360 degrees. "The eyes of hammerhead sharks are bent slightly forward," as BBC Earth put it, "allowing the field of vision of each to significantly overlap."
5. The longest fish in the world is a type of shark.
Reaching lengths of 40 feet long, the whale shark is seriously huge and holds the title of largest fish in the sea. But in the strange circumstance that you encounter one of these in the water, don't be alarmed: their main meal is plankton, which they eat by "filter-feeding," in which they scoop up a huge amount of ocean water and scoop out the tiny plants and animals—it's tough to catch a person in that.
6. Female sharks generally dwarf male sharks.
Partly because they need to carry shark babies, females tend to be larger in most shark species.
7. There are hundreds of shark species.
All told, there are almost 500 species of shark, including angel, bullhead, carpet, and dogfish sharks, not to mention weasel, mackerel, crocodile, zebra, and even catsharks. They range in size from a few inches to 40 feet long, living in a wide range of habitats and boasting a strange assortment of physical characteristics.
8. No, not all sharks live in the ocean.
Just when you thought it was safe to go back into the lake… While sharks live in all of the world's oceans, a few species are also known to inhabit freshwater lakes and rivers. For example, bull sharks are found in tropical rivers and have evolved to swim between salt and freshwater. River sharks, true to their name, have been found in rivers in areas of South Asia, New Guinea, and Australia.
9.Some sharks are pregnant for two years.
You thought nine months seemed like a while, but the spiny dogfish species of shark can take two years to gestate before delivery—making it the longest gestation period of any vertebrate.
10. Yes, you can ride a shark.
The largest species of shark is also one of the most easygoing. Whale sharks have been known to give a ride to hitchhiking swimmers, and cruise through the water atop them. But aquatic life experts caution against popularizing this sport. "When people spend a lot of time and a lot of pressure on a fish, it takes away that slime covering and potentially has negative health impacts for the fish," Marine biologist Bruce Neill told ABC News.