Continuing on a theme of extinct animals that can be resurrected or reinvented in fantasy novels (or even historical novels), one great source for interesting species is islands. So many species from the mainland traveled somehow to islands, became separated from the source species, and evolved down an entirely different pathway, becoming much larger or smaller and/or filling an entirely different evolutionary niche.
An example is the dwarf elephant. Over the course of history, elephants have colonized islands of the Mediterranean, Southeast Asia, and even California! In all cases, the elephants became dwarfed–dramatically so. Each species was different, but the Cyprus Island dwarf elephant weighed in at about 450 lbs, similar to a Shetland Pony.
Think for a moment about an elephant the size of a Shetland Pony. CUTE! And elephants can be domesticated, sort of. Can you imagine a dwarf elephant pulling a pony cart? Maybe acting as a pack animal, in place of a donkey?
I had to resurrect the dwarf elephant for my novel, even though it wasn’t strictly accurate (dwarf elephants were never found on the mainland). I made my dwarf elephants in the 800-900 lb range, a little bit larger so they were more useful, but still smaller than normal elephants. I put a dwarf elephant in the opening scene, mainly as a bit of set dressing. I figured his presence would alert the reader to the semi-tropical setting, and the fact that it was a dwarf elephant would be a red flag saying, “Hey, fantasy world here.”
Only it backfired on me a little. The elephant was so popular that when I didn’t have any followup scenes with him, some of my beta readers complained! So I had to try to create more of a role for him.