"We probably mean the crocodile, an animal similar to the alligator, but larger and more formidable, with a narrower snout and webbed feet up to the ends of the toes. [...] It seems that the word Leviathan refers to the crocodile in Ps. 74:14 and Isa. 27:1. But in Ps. 104:26, this term evidently applies to some sea monster, perhaps to the whale. Various large cetacean animals are found in the Mediterranean. (Philip Schaff)"