Life at the Pole set by Sassafras Lass, from Two Peas in a Bucket
For whatever reason, I had gotten it in my head that narwhals were make-believe creatures, kind of like Bigfoot or the Loch Ness monster. Not true. Apparently, narwhals are real. I consider myself schooled.
At first, I was researching narwhals on Wikipedia, but then I decided I needed a more reputable source. Enter the narwhal profile by National Geographic.
The narwhal in the stamp set is pretty cute.