Not all narwhals have tusks

The majority of tusked animals have tusks on both males and females. However, only about 15% of females and all male narwhals have tusks, which is one of the most interesting facts about narwhals. Researchers find this to be perplexing. Why wouldn't females inherit such an evolutionary feature if the narwhal tusk is, as current studies contend, a method for perceiving the environment? This may provide additional support for the idea that the tusk is primarily a male adornment used to attract attention and establish dominance.

Even more rarely, two tusks have been seen extending on a few narwhals, some of which are on display in the Smithsonian National Museum of Natural History's Sant Ocean Hall.