So, what's with the dolphins? For people of my generation, dolphin characters bring up memories of SeaQuest - which was disparagingly called SquidTrek by many people. (Being as it was essentially a not very good Star Trek ripoff. Well, some people liked it).
I've only had limited contact with dolphins, like most people. Are they as intelligent as us? The jury's still out. They're certainly on the list of animals I won't eat (along with elephants, crow, all primates and the larger squids). No, crow in there wasn't a joke, although none of us want to eat it - birds in the crow family are the most intelligent of all birds. They're at least as intelligent as chimps. In terms of a candidate for a second sapient species on Earth, dolphins are probably it, although a case could also be made for elephants. Both dolphins and elephants pass the "mirror test" - that is they are capable of recognizing their reflection as themselves. The majority of animals mistake their reflection for another animal - as any cat owner who's seen their cat attack the mirror knows.
Using the dolphins was primarily an aesthetic decision. I also wanted to make people think about the other species that share our planet. Should any of them be considered our equals?
I'm a long way from an animal rights activist - I eat meat, after all. But I do question the intelligence of certain specific species. And given how stupid humans can be at times, maybe the dolphins will have the last laugh. Or at least "So Long, and Thanks For All The Fish."