The ancient Greeks certainly distinguished between dolphins and fish. Whether they knew dolphins, unlike fish, were air-breathing, does not seem easy to establish however. The Greek term for whale , giant fish or sea monster was the same one, apparently (κῆτος) and this is what has led to Jonah's tale being sometimes referred to as involving a fish and sometimes a whale: https://en.wikipedia.org/wiki/Cetus_(mythology) The original Hebrew was fish, though. Interesting. I did not know that.
Animals were divided into those of the field, and those of the sea. Whales were the latter, but not kosher because no scales.
Oh good god! They took fish and dolphins out of the water. One type died. The other type were air breathers. Give it up, man.
Why would they identify an air breather with a mammal or land animal? For all they knew, some fish breathed air.
Yeah, they wanted some meat because there was a day they weren't supposed to eat meat, but fish was okay. One day a week. The impoverishment was epic!
Because each will die if it tries to breathe the other. Your questions have degenerated into the moronic.
They didn't know they were called mammals, of course. They certainly knew that they were warmblooded air-breathers who gave birth to live offspring, and then protected them - and that they were very different from waterbreathing, cold-blooded, egg-laying fish.
GS, I don't see your stance to be as obvious as you seem to. I too don't think that people of pre-biblical times (800BC) - when writing their parables - made much of a distinction between different kinds of sea creatures at an anatomical level. It doesn't mean that the naturalists (or whatever biologists were back then) didn't recognize the difference between the animals, but I think it was pretty academic to most. Distinction of creatures back then (there was no such thing as species) was pretty superficial. (Modern science wouldn't even invented for 1,300 years. Taxonomy wouldn't be invented for 1,500 years.) Now, you may be right, or we may be right - but you're way over reaching to assert that your stance is as obvious as you think.
That may be why YOU classify them that way. The question was why the writers of the Bible would classify them that way. And why would you assume that they did?