WHAT SWALLOWED JONAH?

Jonah 1:17  Now the LORD had prepared a great fish to swallow up Jonah. And Jonah was in the belly of the fish three days and three nights. (KJV) Matthew 12:40  For as Jonas was three days and three nights in the whale's belly; so shall the Son of man be three days and three nights in the heart of the earth. (KJV)

While it's true that whales are mammals, and not fish, the Hebrew word used in Jonah (dag) refers to any sea creature which propels itself through moving its tail.  Also, the Greek word used in Matthew (ketos) refers to any large sea creature, including large fish and whales.  So, since either passage could be referring to either a whale or a large fish, this is not a contradiction.