New secrets have emerged about a rare bizarre shark believed to live up to 500 years — and they could hold crucial clues to increasing human life expectancy, scientists say.

The elusive Greenland shark — long marveled for its baffling extreme longevity — does not suffer a significant drop in its muscle’s metabolic rate as it ages, according to fresh research presented this week at the Society for Experimental Biology Annual Conference in Prague.

That’s vastly different from other animals, scientists say.

“Most species show variation in their metabolism when they age,” said lead researcher Ewan Camplisson, a PhD student at the University of Manchester, England, to the Telegraph.

“The results support our hypothesis that the Greenland shark does not show the same traditional signs of aging as other animals.”

Scientists had previously thought that the fish — which is usually nearly blind and doesn’t reach maturity till around age 150 — owed its centuries-long lifespan to its habitat: deep, bone-chilling waters of the north Atlantic Ocean that make for sluggish energy-conserving movements.

But researchers have now discovered the new metabolic muscle clue involving the shark — the world’s longest-living vertebrate species — and say it could end up helping to treat human heart disease.

“We want to understand what adaptations they have that allow them to live so long,” Camplisson said.

“By studying the Greenland shark and its heart, we may be able to better understand our own cardiovascular health. These are issues that become progressively more common and severe with increasing age.”

Little has been known about the creatures — one of the world’s largest sharks — except for their record-breaking lifespan.

One of the beasts, which died in 2016, was estimated to have been born likely around 1620, researchers said at the time.

The scavengers typically grow to around 24 feet and weigh 2,220 pounds while feasting on decaying prey such as polar bears and reindeer, according to the conservation group Oceana.

They are born with relatively small eyes that are typically rendered all but useless because of parasitic crustaceans that eat away at their corneas — but the sharks’ remarkable sense of smell keeps them well-fed as they root out rotting flesh.

Some people say the sharks can enter bodies of fresh water — leading to speculation that one may have been the Loch Ness Monster, Oceana said.

“My ultimate goal is to protect the species,” Camplisson told the Telegraph of his research into the sharks. “And the best way to do this is to better understand them.”