'of yet' and 'as of yet'

The second of doesn't belong to yet but to dinosaurs. He has found dinosaur footprints, but we haven't found bones of those dinosaurs yet. Keeping closer to the given structure, but expressing it formally, you would say:

He's found footprints of dinosaurs of which we have not yet found bones.

So of yet is meaningless. And as as of yet is prolix and graceless, so avoid both and just say yet as tchrist tells you.

The sentence is problematic because of the syntax. A reasonable rewrite that retains the superfluous yet would be:

Most importantly, he’s found footprints of dinosaurs that we haven’t yet found bones of.

A more formal and less verbose rendition of this sentence is:

Most important [1], he has found footprints of dinosaurs for which we have not found bones.

[EDIT: But this is too formal and clunky.]

Most important, he's found footprints of dinosaurs for which we haven't found bones.

As of yet is never any good. It's even more verbose.

You can use yet in a brief response to a question such as:

Have you finished your homework?
Not yet.

Then it's perfectly normal English.

[1]: Sorry, I don't like the /-ly/ form here. I think that adjectives shouldn't end in /-ly/ if they don't need to. Words like homely, comely, and unseemly are adjectives that cannot shed their "ly" without becoming a different word, or, in the last case, a non-word. I also dislike firstly, secondly, etc. But this is strictly a personal style preference.