It definitely is an interesting addition to the article.  The only question is whether you can really justify fair use in this case.  On the other hand, I'm not sure if you can really assert copyright over plain text.  PNAS's copyright policy on submissions suggests that, unlike many other journals, PNAS doesn't demand that you sign over copyright.  The question then is whether the copyright belongs to FTE or to Nick Matzke.  I would suggest sending Nick and email and seeing if he will release the figure under a suitable copyleft license.  

I clearly see it as a valuable addition to the article, one that helps the reader's appreciation of the topic.