Seals and sea lions are fast swimming ocean predators that use their flippers to literally fly through the water.
But how do they do it?
Well, some swim with their front flippers, while others propel themselves with their back feet. These creatures are super-efficient swimmers. New research explains why.
These "underwater acrobats" are ocean predators that use their flippers to "literally fly through the water", a Monash University study said.
"In Australia, we have fur seals and sea lions that have wing-like front flippers specialised for swimming, while in the northern hemisphere, grey and harbour seals have stubby, clawed paws and swim with their feet.
"But the reasons why these two different ways of swimming evolved has perplexed biologists for generations."
They wondered whether one style was better than the other.
The study used computer simulations and footage of live seals to answer this evolutionary mystery.
"The difference in swimming style between forelimb- and hindlimb-propelled seals is so great that these groups were originally thought to have evolved from separate land-dwelling ancestors," said Dr David Hocking, of the university's School of Biological Sciences.
"Genetics clearly shows that all living seals come from the same group of animals."
How, then, could such different swimming styles evolve within the one animal group?
The researchers used advanced fluid dynamics simulations to show how water flows around seal flippers of different shapes.
"Our analysis showed that some Antarctic seals, like leopard seals, actually have very streamlined, wing-like forelimbs, despite being from the 'foot-propelled' seal family," Dr Shibo Wang said.
This is supported by footage of live leopard seals swimming at Taronga Zoo, where they used their front limbs to swim in a similar way to the fur seals and sea lions.
This discovery shows how wing-like flippers can evolve in seals that already swim with their back feet, providing a pathway for the evolution of forelimb swimming in the fur seals and sea lions.
"Wing-like flippers help leopard seals to surge forward and ambush fast-swimming penguins," Associate Professor Alistair Evans said.
"It seems likely that the earliest sea lions also needed this extra speed to capture their preferred prey: schooling fish.
"We finally have a window into the early evolution of swimming in seals."
The study explains the origin of seals, but could also help improve human design.
"Seals have had millions of years to perfect their swimming, and they can teach us a thing or two about underwater grace and elegance," Dr Hocking said.
"Learning from them may help us to improve the design of human-built machines like underwater drones and submersibles, increasing their speed, manoeuvrability or energy efficiency."
Perhaps in future, we'll see seal-shaped submarines? Or how about seal-shaped surfboards? Somebody call Mark Richards.
Jokes of the Day
What do seals say when they get stuck in seaweed? Kelp.
What did the seal say to his mate when he couldn't understand her? Can you be more Pacific?
Why do people share bad seal jokes? Because they're sealy.
