Cladoselache clarki

One of the first sharks to swim in the sea, Cladoselache looked quite different from the killer "jaws" sharks we know today. Its body was shaped like a cigar with a wide tail, and its teeth were far from the vicious killing tools of the modern great white shark. Still, Cladoselache was a good hunter. Fast and agile in the water, it could snag prey with its teeth and swallow the victim whole. "Fast & Flexible: Cladoselache's tail was shaped like a wide 'V,' and it body was long, thin and flexible. This was design wasn't as streamlined as modern sharks' bodies. but it was good enough to allow the ancient fish to chase prey at high speeds and make sharp turns in the water.""Nearly Naked: This fish didn't have the tooth-like scales that armor a modern shark's body, but it did have some protection. Short spikes grew in front of its dorsal fins, which would have stabbed into the mouths of attackers."

Jaws, Past and Present
Cladoselache's jaws looked and worked much differently from those of today's sharks. The ancient fish's hinged jaws weren't recessed under its snout, as they are with modern sharks. Plus, Cladoselache's teeth were shaped much differently. Each of the creature's chompers had three prongs, with the biggest in the middle. These teeth weren't sharp, so the shark couldn't bite chunks of flesh from its victims' bodies. Instead, Cladoselache used its teeth to grab onto its prey, then swallowed them whole. "No Sense: This shark's brain and nasal cavities were small for the size of its body. Experts think this means that Cladoselache's sense of smell wasn't good, and it lacked the keen sense that today's sharks have. This beast probably hunted by sight only.""Run Away! Beyond hunting, Cladoselache had a good reason to be a fast swimmer. It shared the Devonian oceans with 20-fot predator called Dunkleosteus. This beast had the deadliest jaws in the sea, but Cladoselache could have out swam it in most chases."