Well the coccyx isn't actually fused in most people. It usually has several jointed bones in it. It's what's left of our tail, but it's certainly not "snapped off". It's just not as long as some other tails. There are still a lot of important bits attached to it (ligaments, etc) so it's still functional, even if you wouldn't think so.
Anyway, let's talk fish. Humans, like all vertebrates, evolved from fish. So, rephrasing your question: if humans evolved from fish, why are there still fish? Well, there are, whether you like it or not. Sure, modern fish aren't identical to our common ancestor with them (although some are suprisingly close) but they're still fish.
Similar situation with apes. We have a common ancestor with gibbons. It wasn't exactly like a modern gibbon, and it wasn't exactly like any modern human (apart from a few weirdos in Deliverance country). However, this common ancestor was still an ape. That's why we can have evolved from apes and there can still be apes around today. In fact technically humans, including you,
are apes. So it's not really accurate to see that we "evolved from apes". A better way of putting it is to say that we evolved from an ape that was rather different to our modern apey selves.
I know what a caveman is.
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My point was that if you're talking fairly recent hominins (like us) then unless you go back way more than 100,000 years, you probably wouldn't be able to tell them from modern humans, assuming both were dressed the same and had a decent haircut. IOW, all the ice age cave paintings and whatnots that you read about were done by people who were pretty much just like us, apart from a less advanced technology.