This is not the official gender differences. The Pokemon Riolu doesn't have any gender differences. But this is just something I've created to show how I like to draw my female Riolu's and male Riolu's. The reason the male Riolu looks more like the official version is because you can easier capture male Riolu's than female ones. These "rules" of their gender differences doesn't have to apply to ALL female/male Riolu's. If you take a look at Aaron, you'll notice he has almost all male features, but he has bigger eyes than a normal male Riolu has, also a longer tail but the rest of his features are male, so it's a mix. I usually mix the features a bit because I want them to look...."more girly" at times. Like this guy [link] he has long eyelashes even if he's a guy, he's a bit shorter than Aaron and his ears are kind of fluffy but you can still sorta tell he's a male riolu. The eyes are also just in my manga-ish style, i'd do the same thing to their normal eye-style if i drew it up, so it's not so much of a difference.
You can use this if you want. I'd be honored really XD
I hope this cleared up some things with my riolu-anatomy and how I like to use it. I know it still needs a LOT of work but I'm going to improve little by little starting now. I hope you enjoyed this drawing >w<)/. And i also hope it was helpful .w. PS: Sowwiiii for any spelling fails if you find them -w-. You can count this as a small tutorial or reference o3o....*goes to draw more pokemon*