In the first photographed example of friendliness between them, humpback whales and bottlenose dolphins were seen off the coasts of Hawaii playing with each other, according to a January report by the American Museum of Natural History.

They have little reason for politeness other than a shared living space, but in two separate instances, scientists say, dolphins hitched a ride on the heads of whales, then slid down like a sea-bound playground.

The whales lifted the dolphins up and out of the water, then calmly let them ride back down.

The peer-reviewed science journal Aquatic Mammals reported a similar finding in 2010, also from Hawaiian waters.

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