I like your idea. No one says it can't be artistic. Look on pinterest and see if someone's pinned something along those lines. Maybe change things up? One wall science, another space, another music, etc. Have one wall for zoology--there's your animals. If you do it right (not too many colors clashing all over) and/or make it subtle, you can do a lot. Do the animals in soft hues, the others tone on tone.
meet the wife half way and go for photo realistic posters of great white sharks, snakes and close ups of various bugs