Clue problem?

[cranberry44]

I built a 15 X 15 around the entry "extinct man." The clue is "A happy slave," to William Lloyd Garrison, on dispelling the myth of "the happy slave" (with "an"). When I chose the entry, I didn't realize how difficult it would be to come up with a concise clue. It's much too long but I can't seem to shorten it. I think I do need to include words re: myth. Any suggestions? The quote is found in Garrison's preface to "The Life of
Frederick Douglass."

[cranberry44]

Do you think I can change clue to "One known from a fossilized skeleton found near Tepexpan"? Or would the answer "extinct man" be considered "green paint"?

Alternate clue could be "A happy slave," per William Lloyd Garrison (with "an).
(The quote "A happy slave is an extinct man" is found many times on the Internet
because it's part of the preface to Friederick Douglass's narrative. But it is difficult to discern answer from this clue.)