Sadly, no. A species does not evolve into just one new species. They evolve into multiple new species resulting in a group. Narwhals belong to the Cetacea group along with whales and dolphins. Which means the narwhal's ancestor is the same as that of dolphins, orcas, ...FallenTraveler said:that literally just made my day. Favorite animals are narwhals.theonlyblaze2 said:Narwals have a vestigial pelvic bone. This means that at some point, Narwals walked on land. Therefore, Unicorns.
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What exactly this ancestor is has been a mystery for ages (Darwin himself once hypothesized it was a bear, lol) but recent-ish fossils like Rhodocetus sp. and Basilosaurus sp. look promising. (I'm too lazy to post images you can google for yourself)
So that leaves 2 options: either the Cetacea's common ancestor had a horn (which is actually just a giant tooth) and all Cetacea but the narwhal lost it. Or the common ancestor did not have a horn and the narhwal gained it on it's own. The second option seems way more likely though especially if you look at the fossils I mentioned.
Anyway the point is: narwhals evolved from the same ancestor as whales and dolphins, which likely wasn't a unicorn.