Tusks, those ivory spears that protrude from the jaws of certain large mammals, are actually elongated teeth. Ivory, the stuff they're made of, is a type of dentine calcium-rich tooth tissue .
The tusks of elephants and narwhals are modified permanent upper incisors, whereas the tusks of walruses, warthogs and wild boars are outsized canines .
There's no one reason that tusks evolved from teeth in so many different species. Elephants use them to dig and bore. Male narwhals spar with them to impress narwhal-ladies. Walruses use them like picks, to grip ice. Boars use them as weapons.
The largest tusk ever recorded belonged to an African elephant . It weighed 214 pounds and was 11 feet six inches long.
Original story on Live Science.