A shark that lives for almost four centuries could hold the secret to long life, say researchers.
Greenland sharks, with a lifespan of up to 392 years, are thought to possess unique longevity genes now being searched for by scientists.
Professor Kim Praebel, from the Arctic University of Norway, who is leading the hunt, said: "This is the longest living vertebrate on the planet.
"Together with colleagues in Denmark, Greenland, USA, and China, we are currently sequencing its whole nuclear genome which will help us discover why the Greenland shark not only lives longer than other shark species but other vertebrates."
The team has taken fin clippings from almost 100 Greenland sharks, including some individuals born in the 1750s.
Already the researchers have mapped out all the 16ft shark's mitochondrial DNA - genetic material held in tiny battery-like bodies in cells that supply energy.
Now they are working on DNA from the cell nucleus, which contains the bulk of the animal's genes.
The "long life" genes could shed light on why most vertebrates have such a limited life span, and what determines life expectancy in different species, including humans.
Little is known about the biology and genetics of the Greenland shark, which inhabits deep water in the Atlantic ocean from Canada to Norway and is found off the coast of Scotland.
Prof Praebel added that the sharks were "living time capsules" that could help shed light on human impact on the oceans.
Many were so old they pre-dated the industrial revolution and the introduction of large-scale commercial fishing.
The shark's tissues, bones and DNA could also provide clues about the effects of climate change and pollution over a long time span.
"The longest living vertebrate species on the planet has formed several populations in the Atlantic Ocean," said Prof Praebel, who was speaking at the University of Exeter at a symposium organised by the Fisheries Society of the British Isles.
"This is important to know, so we can develop appropriate conservation actions for this important species."