2. Tigon Tigon is an animal resulting from a cross between a male tiger and a female lion. They are smaller than ligers and often resemble their lion parent in appearance, with faint tiger stripes.

You can read more about ligers here. Nobody could fault you for thinking a tigon should basically be the exact same animal as ...

Do they challenge the definition of species? Not really. The key words are "interbreed successfully"; tigons and ligers generally are sterile and short-lived -- an evolutionary dead end.