Leviathan
a transliterated Hebrew word (livyathan), meaning “twisted,” “coiled”
a sea monster
The “leviathan” the Bible talks about in Job 41 is described as the greatest creature in the sea. Unlike a crocodile or fish, it was useless to try to catch a leviathan with hooks, harpoons or anything else. “Nothing on Earth is his equal—a creature without fear” (Job 41:33, NIV).
What was a leviathan? The large size, strong jaws, great teeth, fast swimming ability and its protected back and underside all give clues. It could have been a Kronosaurus (pronounced: KRON-oh-SOR-us) or something like it. This was one of the greatest, most overwhelming animals ever to swim the seas. It was not a true dinosaur, but it was reptile-like and had great, sharp teeth.
It seems these animals were still alive at the time of King David. Psalm 104 says they played where the ships go to and fro. This was probably the Mediterranean Sea.
It is interesting that many reports of “sea serpents” closely match the ancient pliosaurs and mosasaurs. They looked somewhat like huge lizards or crocodiles with flippers or webbed feet. Fossils show their backbones were very flexible. They could probably swim in a snake-like motion.
More information