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Whoever wrote the Pokedex information didn't even pretend to be interested in Sandshrew's classification, which is ironic considering the series has gone lengths to give arbitrary differences in male and female genders of most species. "What's the point of your classification prattle?" Same as always. Stop taking the game's given information so seriously and start thinking realistically for yourself.
If you recall, I mentioned that just because Nidoran have hair doesn't mean that they are fuzzy creatures by the traditional association, but that might not be completely incorrect. Watch this movie.
Professor Oak's Lecture: Nidoran - 10.5 MB (ed. to be youtube'd 5/13)
Here's a clear image of the most important part, click to enlarge.
Now, what kind of mammal can possibly ruffle up like that if it's just had smooth skin? Ignore the stock electricity sounds, because Nidos aren't electric. But it's definately ruffling or brusseling something in order to poison Professor Oak. I admit this is pretty easy to miss because most people haven't had access to this clip (until now, Nido wise anyway, but you know me, I'll get what you need when it comes to Nidos). Much like a cat can make its hair stand on end, or a porcupine that can expand its quills, maybe? Now we're on to something, and there's supporting evidence even in the games themselves. Recall that Nidoqueen's Pokedex information mentions evolving to have scales that can stand up on end.
Heck, it's even pictured here.
Looks like this trait is something that it could also do in earlier stages. Read up on Nidorina's information and it mentions being able to contract thorns when it's relaxed. Those big things on her back? Since when have those ever retracted? It's possible that it may have meant that, but even in Pokemon Stadium, those large back spines appear pretty immobile. Plus, checking the other Professor Oak Lecture, Nidorina poisons Oak just by touch alone. There's no animation of anything standing on end, which could mean glandular, but then again, it's pretty lazily animated in the first place, using a very stock pose for Nidorina (I tell ya, she gets no respect). So lets say these thorns were all around her body, like a hedgehog, who could also retract and expand its thorns, or quills if you will. And you know what? The quills of an animal such as a hedgehog or porcupine is...guess what... modified hairs. So, it all comes back to hair! Basically, what I'm getting at is that either Nidoran is fuzzy with posionous glands in the skin, or is covered with expandable quills like a hedgehog that secretes poison, and since the series goes on about secreting poison through horns and spikes, and not by glands (unlike Umbreon, for example), I personally believe that Nidoran are covered with quills. Makes sense once you bring all the facts together. To recapitulate, here's a visual aid.