Orthacanthus

Orthacanthus was an ancient, fresh-water shark that had a long spine growing from the back of its skull. It had a very long dorsal fin, which ran all along the sharks back, giving it an eel-like appearance. 
"Orthacanthus" was the terror of freshwater swamps and bayous in Europe and North America. Its body reached nearly 10 feet (3 meters) in length and its powerful jaws were lined with double-fanged teeth.
"Orthacanthus" lived from roughly 280 million years ago, from the Pennsylvanian period through the Permian period. They were around before the dinosaurs evolved.