Sharks are ancient creatures. Take any biology course that covers ancient life and they will tell you that sharks have been around for a darn long time. They do not technically have bones and thus, like lampreys, are considered very primitive fish. They have had thousands of years to perfect the art of devouring anything stupid enough to drip a single drop of blood into the water.
But even Jaws had an older relative. A much creepier, much older relative:
Frilled sharks (Chlamydoselachus anguineus) are rarely-seen, but when they turn up, they cause a stir. No wonder; that shark can reach up to two meters in length and looks like something found only by staring into the abyss too much. That is not too far from the truth - frilled sharks live mostly in the deeper waters where humans dare to tread, but are caught more frequently and at shallower depths in Suruga Bay, Japan. Go figure; it's found in the two places known for monsters.
Don't look in its eyes...
One glance is enough to tell you that the frilled shark is not a normal shark. Its namesake gills look somewhere between a regular shark's and a salamander's; it lacks the triangular dorsal finand streamlined build that most people associate with sharks; even the head looks off, with those teeth like small pine trees, that strange bluntness, and dead eyes that freeze your soul. It eats fish, cephalopods, and other smaller swimming things in a style befitting a snake. This thing is not just a living fossil; it is a fossil given Lovecraftian reanimation treatment, then set loose in the depths of the ocean for kicks.
Clearly, this is what happened.
That said, it really is that old. Sharks in general have skeletons made out of cartilage instead of bona fide bone; this shark barely has distinct vertebrae. Those gills make the operculum look like an awesome invention. This shark is just barely a genuine fish, even if it has evolved slightly in the past few millennia. (Oh, and by the way, it's one of those sharks that gives birth to live babies just to freak you out more.) The frilled shark makes the coelacanth look like a newborn.
Forget Jaws. This is the shark that will be haunting your nightmares from now on.