While the discovery made for some heady news releases, and excited anyone in the field of radiocarbon dating, it also raised a pretty serious question. That is, how do some animals live for so long, while others—like humans—only get a few decades?

In August this year a team of marine biologists came up with an ingenious method of radiocarbon dating sharks in Greenland. Doing so, they found one female specimen was 400 years old. She was a five-metre shark, probably born sometime around the death of Queen Elizabeth 1.

This definition doesn't include the extra biological time amassed by cases of suspended animation—such as the Tardigrade, otherwise known as That Water Bear everybody loses their shit over. Tardigrade have relatively short lifespans but can theoretically exist forever based on their ability to take biological timeouts, which is cheating.

Dr Sarah Milton of Florida Atlantic University attributes negligible senescence to "adaptations that permit both extended anoxic survival and recovery." In other words, the ability to survive long periods without oxygen, as well as being able to recover rapidly from those periods. Both set organisms up for surprisingly long lives.

Negligible senescence is basically defined by a lack of ageing, the absence of functional decline. Such a phenomenon explains some seriously long lifespans, such as the alleged 255-year-old Aldabra giant tortoise, which died in 2006 at India's Kolkata Zoo. Or the 507-year-old ocean quahog clam that was caught off the coast of Iceland in the same year.

To understand, we'll need to get a little technical. The concept of senescence refers to biological ageing. The precise mechanism behind human senescence is very complicated; however, it's fair to say we experience the progression of ageing differently to many other species. Theoretically, some animals will never die of natural causes.

According to American physicist and popular science pundit, Dr. Michio Kaku, crocodiles have no recognised finite lifespan. Instead, they just get bigger and bigger until they're inevitably killed out by "starvation, accidents, or disease." This is the reason we don't happen to see crocodiles the size of Boeing 747s in the wild.

If you're looking for the poster child for negligible senescence you need to think bigger, specifically, the saltwater crocodile.

Dr Kaku also claims the standard 70-year crocodile lifespan defined by textbooks is basically because "zookeepers die at 70." While this may sound like some sensationalist science reporting, there are undeniable facts we have to take into account.

For a start, saltwater crocodiles have the well-documented ability to survive without oxygen for over two hours. They also do not require lengthy recovery times following these anoxic periods. Animals such as whales can survive three hours at the bottom of the ocean hunting for squid, but require approximately double that time to recover. Crocodiles simply come up to breathe and can immediately submerge themselves again.

All of the mechanisms supporting anoxia, such as hypometabolism and the induction of various protective proteins, are associated with some serious longevity in animals.

It should also be noted that crocodiles don't appear to deteriorate with old age. They are as vigorous at 70 years old as they are at five, suggesting that they don't experience a decline after reaching sexual maturity.