The mammal with the longest life expectancy is the bowhead whale. Although they were once thought to have a 50 to 70 year lifespan like other whales, it is now estimated that they can live to be 200 or older.
Usually, age in animals is estimated using the teeth, and because bowhead whales lack them, it is difficult to estimate their age. Scientists did not know that the bowhead whale had an unusual lifespan until some interesting specimens turned up during whale hunts. These whales had embedded harpoons and spears in them that could be dated to at least 100 years prior, according to the University of Alaska Fairbanks. One discovered in 2007 had an embedded harpoon linked to production in New Bedford, Massachusetts, in 1890. Scientists then used chemical evidence from bowhead whales' eyes to estimate their ages, and they found one specimen with an estimated age of 211 years.