The Greenland shark likely lives at least 400 years, making it a strong candidate for the world's oldest vertebrate species.
The carnivore doesn't even reach sexual maturity until age 150, according to a new study published this week in the journal Science. The international team of scientists was led by Julius Nielsen of the University of Copenhagen in Denmark, and included researchers from Greenland, Norway and the United States.
The researchers performed carbon dating on the eyes of 28 female sharks that had been caught as accidentally by fishing boats in Greenland.
They looked through the layers of the eye for levels of carbon-14, a particular carbon isotope introduced into the environment during nuclear bomb tests beginning in the 1950s.
The eyes develop while the shark is still in the womb, and levels of carbon-14 would be higher if the shark's mother was pregnant in the 1960s, when carbon-14 levels made their way into the food the shark's mother would have been eating.
The team found that most of the sharks were older than 50 years. The researchers then used this benchmark to estimate how old each of them were. Greenland sharks grow at an extremely low rate of about 1 centimeter per year.
Simply by measuring the sharks, Nielsen and his colleagues figured the oldest shark was about 392 years old, the second largest shark was about 335 years old, and the average lifespan of the total sample was at least 272 years.
This would make the shark older even than the bowhead whale, which is thought to live 211 years.