l that lived more than 20 million years ago along the ancient shores of Northwest America.
Like the living northern seals, Enaliarctos had long claws and flexible finger joints, suggesting that it would have been able to grasp prey during feeding. But unlike living seals, Enaliarctos also had sharp cutting teeth similar to those found in its meat-eating, land-dwelling cousins.
To use these teeth effectively, Enaliarctos needed to place food carefully in its mouth. This is a difficult task when floating in water, but holding onto prey with its hands would certainly have helped. Perhaps Enaliarctos even still brought its quarry ashore, much like living river otters.
Later seals lost the sharp cutting teeth of Enaliarctos, but retained its ability to grasp prey.
This gradual transition helped to smooth the switch from feeding on land to hunting underwater. Rather than changing all at once, the behaviour and anatomy of early seals changed gradually, remaining effective at each step along the way.
Clawed forelimbs: a relic of the ancient past or useful modern adaptation?
Given the importance of clawed forelimbs to ancient seals, why are northern true seals the only ones that still use them?
The answer, partly, is simply because they could. Unlike their close relatives, the fur seals and sea lions, northern seals primarily swim with their hind limbs. Their paws thus remained free to perform other tasks, and simply kept doing what they always had done.
But there is also a more sinister part to this story. Mobile paws may give seals an advantage when handling large prey. Grey seals, in particular, have put this skill to deadly use.
For years, scientists have noted carcasses of harbour porpoises and various seals with peculiar spiral injuries. The true nature and cause of these wounds was revealed only recently.
Grey seals prey on other marine mammals, using their paws and claws in the process. Somewhat shockingly, they even fed on members of their own kind.
Their claws connect northern seals with their ancient past, and help us understand how their ancestors conquered the ocean. Cases like the grey seals also show that claws are not just an evolutionary hangover. Instead, they remain a key tool, allowing northern seals to exploit niches not – or perhaps no longer – available to most of their kin.