I know this might not be the best place to ask this, but does 'staart' have the same colloquial meaning it's German counterpart 'Schwanz' which can also refer to a man's penis?
Thank you. I'm not trying to perv everyone out, I was just curious.
You would never say "Cat is a social animal." Or, "I like to drive car." The singular thing is only true of man that I can think of, unless you're talking about meat. "I like to eat cat."
You could of course say "A cat has a tail." But in this case what you're trying to say is that if I pick any random cat it'll have a tail. Which is functionally equivalent to cats have tails (meaning all cats have tails), but it sounds funny and no one really says this unless you're speaking to a child.
Anyway I wouldn't say it's common at all. I'd say we usually use the plural to talk about classes.
A quick etymological search paints a muddled picture. As Nierls says, some sources relate it only to ancestral words basically meaning a stiff thing sticking out, such as the handle of a plough (cognate with German adjective "starr" stiff).
Some relate it together with English "to start" (where the meaning "move suddenly" seems to be the original one) to Dutch "storten", to fall/tumble/plunge. Which might also be related to the root meaning "stiff", though I don't quite understand how...
In summary, they may have a distant common ancestry, but nothing indicates it developed from people saying, the animal starts = begins here (which in my mind would have been the wrong end to point to anyway...).