Protosphyraena was a medium-size predatory fish of the Late Cretaceous seas with a long swordlike snout and bladelike teeth positioned to stab fleeing prey. What's more, one of these ancient fish had long, bony pectoral fins with leading edges serrated like saw blades. While the exact purpose of these sawlike fins is a matter of scientific debate, no doubt this fish was armed with lots of potentially offensive weaponry.

Fully grown adult Protosphyraena averaged between six and nine feet (two and three meters) long, an unremarkable stature in oceans ruled by mosasaurs and plesiosaurs that grew more than 35 feet (11 meters) long.

Complete skeletons of Protosphyraena are rare, which may suggests that either scavengers devoured them or the corpses drifted as they decayed and fell apart. Like some Late Cretaceous sea monsters, Protosphyraenamost likely went extinct 65 million years ago.