Toothed whale porpoise as a fish. Toothed whales, as well as baleen whales, are descendants of land-dwelling mammals of the artiodactyl order (even-toed ungulates). They are closely related to the hippopotamus, sharing a common ancestor that lived around 54 million years ago (mya). The primitive cetaceans, or archaeocetes, first took to the sea approximately 49 mya and became fully aquatic by 5–10 million years later. The adaptation of echolocation and enhanced fat synthesis in blubber occurred when toothed whales split apart from baleen whales, and distinguishes modern toothed whales from fully aquatic archaeocetes. This happened around 34 mya. Unlike toothed whales, baleen
What Is and What Should Never Be (Supernatural) creepy look to it". He was pleased to see Smith and Palicki return, and found the character of Carmen to be "a nice addition to the family". Don Williams of BuddyTV agreed, and ranked the episode third in his list of the best episodes of the first three seasons. Deeming it the best standalone episode, he noted that it "can be embraced by anyone who enjoys clever writing, great acting, or a shirtless Jensen Ackles". General Specific Notes What Is and What Should Never Be (Supernatural) "What Is and What Should Never Be" is the twentieth episode of the paranormal