[undersuit]

All Cetaceans have blowholes. I think it's one of the original evolutionary traits.

"The trachea only connects to the blowhole, and the animal cannot breathe through its mouth." https://en.wikipedia.org/wiki/Blowhole_(anatomy)

[masterponomo]

I can see where natural selection would lead to separation of the blowhole from the mouth. I'll bet proto-whales without that adaptation had frequent clogging of the blowhole with food from within. This would not only block the airway, but blowing the food out (if they could manage it before blacking out and sinking) would deprive them of nourishment.