Echolocation in dolphins and bats evolved separately, but through the same genetic changes.
"The natural world is full of examples of species that have evolved similar characteristics independently" said Stephen Rossiter. "However, it is generally assumed that most of these so-called 'convergent traits' have arisen by different changes in the animal's DNA. Our study shows that this very complex ability - echolocation - has in fact evolved by identical genetic changes in bats and dolphins."
Ref.: Convergent sequence evolution between echolocating bats and dolphins. 2010. Y. Liu, et al. Current Biology 20: R53-R54, 26.