There's been so many good suggestions already, it's hard to think of much to add. But I thought I'd elaborate on the suggestion of dolphins.
There are actually a fair variety of dolphins - we don't have to go with just the gray bottlenose (not that there's anything wrong with them!)
There's also
Commerson's Dolphin, a funny looking - and cute - stocky black-and-white dolphin,
the
Common dolphin, a rather colorful dolphin, in shades of gray with a yellowish stripe on its side, and often featured in ancient
Greek art ,
Risso's dolphin, an unusual dolphin that collects scars on its hide over it's life,
the
spotted dolphin which is... spotted, and kinda like the Risso's, collects more spots over its lifetime,
the
Dusky dolphin, which I consider to be a quite pretty animal, being in hues of creamy white and gray and shadowy dark gray
Spinner dolphins, which have long, pointy beaks and are known for their fantastic breaching antics, particularly their amazing spinning,
and the
Indo-Pacific Humpbacked dolphin , which can be white or pink! And of course we probably all know about the killer whale/orca, actually the largest of the dolphins! And more not mentioned here.
So, when it comes to dolphins, there's plenty of variety to inspire our artists!