Barbara Bernát is a graphic designer and for her MA degree project she designed a complete set of Hungarian paper money.
Note each side of the bills: the front side an animal, the back side the related species of plant. As you scroll down the page you can see her entire process. It’s a great project and a great documentary post about it.
The kicker is at the end of the post: If you hold the notes under UV light you see the skeletons of the animals.
This reminds me of the work of the late Donald Evans who hand-painted complete sets of postage stamps from countries he made up.
Note: You can still purchase the out of print book documenting the amazing work of Donald Evans: The World of Donald Evans. I have a number of copies, including a first edition hardback.