Sunday, 22 April 2018

Sharp claws helped ancient seals conquer the oceans

April 18, 2018 by David Hocking And Felix Georg Marx, The Conversation

If you've ever seen seals frolicking in the water, you know they are agile swimmers, with perfectly adapted paddle-like limbs. But if you think those flippers are just for swimming, then think again.

In a study published today in Royal Society Open Science, we took a fresh look at how one group of seals – the northern true seals, including grey and harbour seals – use their forelimbs to process and eat their prey. This behaviour is rare among living marine mammals, and shows how ancient seals evolved to feed in water.

What's in a flipper?
Seals are best known for having long, streamlined forelimb flippers, much like those of a dolphin.

Flippers and fins are great for steering and swimming, and independently evolved in many aquatic vertebrates: fish, seals, whales, dolphins, turtles, and extinct marine reptiles such as plesiosaurs and ichthyosaurs.

But northern seals are an exception. Rather than wing-like, their hands are short, with mobile fingers that end in large protruding claws.

Instead of flippers, they really have paws—more like a dog than a dolphin. The question is: why?

The clawed seals of the north
The answer has to do with how these animals eat. When watching how northern seals feed, both in captivity and in the wild, we found that they don't just take a bite out of their catch.

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