God takes all of Job 41 to describe a fierce sea reptile called leviathan. The description is of a very intimidating, fire breathing sea reptile. It is most likely one of the aquatic dinosaurs.
Some claim that leviathan is a crocodile, but there are problems with this idea. First of all, have you ever heard of a fire breathing crocodile? Furthermore, Isaiah 27:1 referred to Leviathan as "the dragon that is in the sea." and crocodiles are not found in open sea. Finally, the overall description is of the animal does not fit a crocodile. Leviathan seems so fierce that it would make a crocodile look tame in comparison. So Leviathan was most likely one of the aquatic dinosaurs and clearly not a crocodile.
By the way, it clearly got Job's attention.