The Greenland shark can live for up to about 400 years, making it the longest-lived known vertebrate.
Scientists estimate its age by analysing proteins in the lenses of its eyes, which form before birth and remain largely unchanged. Radiocarbon dating of eye-lens tissue showed that some Greenland sharks were several centuries old, with one large female estimated at roughly 392 years.
These sharks grow extremely slowly, at around one centimetre per year, and may not reach sexual maturity until they are more than a century old. They inhabit cold North Atlantic and Arctic waters, where their slow metabolism suits the frigid environment.
The estimate is not an exact birthday. It is a scientific age range based on radiocarbon evidence, so references commonly describe the species as living up to around 400 years rather than claiming a precise lifespan for every individual.