Dolphins apparently create a signature whistle shortly after birth and share that whistle as if it were a name when they meet a new ally or dolphin:
From Discovery Magazine:
"... The signature whistles seem to act like badges of identity. One dolphin can learn information about another by listening to its whistle. But they’re not entirely like human names. For a start, they’re invented, rather than bestowed. They also convey more than just identity – they reveal the caller’s motivation or mood. "It’s a bit like in human language, where you can hear if a person sounds happy or sad, not in the choice of words they make, but in subtle acoustic features in their speech," explains Janik. ...