Sentence:  It features in textbooks as well, a prime example of a "<WSD>living fossil</WSD>", a reminder of past glories now hanging on in a last-ditch action against final extinction. But is nautilus really an anachronism? 
Meaning of the word marked with <WSD> tags:  Any species discovered first as a fossil and believed extinct, but which is later found living; an organism that has remained unchanged over geological periods. (from 1859)