Hmm... I would have assumed that interpreting dolphin sounds as pictures is the first thing you'd try after realizing they can echolocate... Is this really the first time that's been explored? Or is it just that no one's been able to figure out how to reconstruct an image properly from dolphin clicks, but it was already a widely suspected possibility for a long time? (I'm not really up to date with dolphin research, unfortunately.)

If they're right about this line of reasoning, then I wouldn't be surprised at all if they come back and point out an animation structure soon (akin to sound detection of a moving object over time) -- and if that's the case, I'd bet you that it isn't "universal", and that different groups of dolphins will have different variants in how they communicate more complex concepts. For example, one group might give an animation of a dolphin swimming around something in one direction a meaning that a different group might disagree with. Another sort of animation that might be interesting to look for would be a change in the composition/texture of an object (e.g. animation of dolphin turning to stone, or stone turning into dolphin or something like that). It seems reasonable to me that even if you communicate in animated 3d images, you'd probably still have to have some less literal meanings too... and the sorts of things you could represent with something like that could get pretty complex, actually.