A group of dolphins has learned to protect their noses by lancing a sea sponge and wearing it like a glove on their snouts while digging for worms. This behavior appears to be passed down by demonstration, and only from mothers to daughters. (Seeing grandma doing it clinched the matrilineal hypothesis.)
The only other species that are known to pass on cultural ideas are great apes, who teach each other how to use tools such as hollow reeds to suck ants from anthills. Birds pass on songs, but in isolation they're still programmed to sing, just not the same tunes as each other.
The aquatic mammals seem ever more clever than we previously thought. And they're cross-breeding to perfect their genetic edge, creating the unbeatable 'wholphin'. The inter-species war scenario The Simpsons warned us about in Treehouse of Horror IX: Night of the Dolphin can't be far off.
Is this a bad time to mention that Hurricane Katrina released a group of "armed dolphins, trained by the US military to shoot terrorists and pinpoint spies underwater" who may be "missing in the Gulf of Mexico"?
P.S. If we are attacked by terminator dolphins, we'll need intrepid scientists like biologist Frank "yeah, I know it's apropos" Fish. Investigating "spinner" dolphins, who twist up to seven times in a single leap into the air, Fish hypothesized that perhaps the dolphins were attempting to shake off ramoras. But don't most large aquatic animals like teaming up with ramoras? To understand why having a ramora might be unpleasant, Fish attached one to his back. Turns out it's pretty painful. Way to take one for the team, Fish!