[Epona]

I thought Liger/Tigon hybrids were a fairly well known phenomenon, not as common as mules.

Similar species within a genus can hybridise but the offspring are usually sterile, it occurs in the wild sometimes but more often in captivity or where numbers in the wild are low due to lack of choice. It's quite common amongst birds (ruddy ducks are causing a problem in one part of the UK because they are hybridising with a similar species, there is a danger the other species could die out as a result), especially parrots because most of them form life-long monogamous bonds with one partner - so sometimes they'll pair up with a mate from a different species, they seem quite irrational when picking mates - it's either hate or love at first sight. My parrot thinks I am his bonded mate and I'm not even a bird (at least not of the feathered variety!), so there you go.