Narwhal has the strangest tooth in the sea

narwhal illustration

TWISTING TOOTH  Most narwhals grow only one, the left tooth, and it always spirals to the left. Even in the rare cases where a right tusk emerges too, it also spirals to the left instead of having the mirror symmetry usual for mammal body parts. Narwhal tusks can grow to half the animal's body length.

W. Scoresby/Wikimedia Commons

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Sometimes called the unicorn of the sea, the male narwhal’s tusk is actually a tooth, and it grows directly through the whale’s upper lip instead of pushing the lip aside. It’s an exuberantly large version of a canine tooth that grows in a spiral; the only tooth known to do so. Otherwise narwhals are practically toothless, with only vestigial stubs that stop growing during development and rarely emerge into the mouth.

This extreme anatomy has captivated dentist Martin Nweeia, who practices in Connecticut and teaches at Harvard University. For more than a decade, he has pioneered ways to study these difficult-to-reach Arctic whales, and he and his colleagues now describe in the April Anatomical Record that narwhals can detect changes in water salinity using only their tusks. The animals “don’t have a good sense of humor,” though, about being temporarily restrained for the testing, Nweeia says.

ANATOMY OF A TOOTH Unlike human teeth, no enamel protects the outside of a narwhal tusk. Kevin Hand, M.T. Nweeia et al/Anatomical Record 2014
SENSITIVE TEETH Abundant pores in the outer layer (cementum) allow the salinity of surrounding water to trigger special cells called odontoblasts that connect to nerves in the tusk’s inner pulp. Heart rates increased in living narwhals when researchers changed the water salinity around the tooth. Kevin Hand, M.T. Nweeia et al/Anatomical Record 2014
FEELING PAIN Studies of narwhal tooth anatomy reveal an extensive sensory network and production of substance P, linked to sensing pain. Kevin Hand, M.T. Nweeia et al/Anatomical Record 2014
FEMALE TEETH Only 15 percent of female narwhals have a tusk (blue) that emerges from the skull. Both sexes also have tiny vestigial teeth (green), not useful for eating. Ethan Taylor, M.T. Nweeia et al/Anatomical Record 2012

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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