In their relentless quest to one day surpass humankind as Earth's premier beings, dolphins have intermittently revealed some remarkable qualities signaling a highly advanced intelligence. One fairly recent study suggests they can form complex, hierarchical gangs to guard their turf from rivals. More recent research confirms that, like humans, the mammals often call on one another by name.

And now, according to a new study from animal behavior scientists at the University of Chicago, researchers have discovered that dolphins are really good at remembering things, especially when it comes to an old friend.

First, it's worth noting that assorted studies have suggested that some land-based mammals possess pretty keen social memories, too. Monkeys can remember one another for up to four years. And anecdotal evidence indicates that frumpy ol' elephants can remember their kin even after being separated for 10 years.

But dolphins blow them all out of the water, so to speak, capable of remembering their long-lost pals even after being separated for 20 years. If you're keeping score, that's far and away the best of all Earth's non-humans. (And many actual humans, too, for that matter.)

Study co-author Jason Bruck analyzed the whereabouts of 56 bottlenose dolphins scattered around the country. To promote better breeding habits, the animals had been shuttled back and forth between different institutions — aquariums, zoos, you name it — over a period of 20 years.

This provided Bruck with some fairly detailed records about which dolphins had spent time together. So, Bruck and his team set out to record the signature whistles — or what's thought to be the "names" — of 43 of the dolphins, and played a bunch of different calls to the animals via underwater speakers.

When the dolphins heard the calls of animals they didn't know, they ignored them. No surprises there.

But when it was the unique whistle of an old acquaintance? The dolphins whistled back, even if they hadn't seen the other animal in decades. "I was just blown away," Bruck told LiveScience.

It's not really clear why dolphin brains are coded with the capacity for long-term social memories. And not everyone buys that the animals were actually responding to the recorded whistles of their old friends. "Is this really about the dolphins that produce these whistles, or is it just about the sounds themselves?" Heidi Harley, a dolphin researcher who wasn't involved in the study, told the Washington Post. "It's a little hard to disentangle sometimes."

Kind of like some friendships, no? I wouldn't be surprised if dolphins had frenemies, too.