Great advances have been made during the past 20 years in retrieving and mapping ancient DNA. The techniques used are truly remarkable, and DNA is routinely being obtained and analyzed from fossilized or long-dead human and animal remains. Usually the DNA is extracted from a thigh bone, other large bone, or teeth.
For example, a rough draft of the entire Neanderthal genome, completed in 2010, led to the discovery that Neanderthals interbred with ancestors of modern humans. This is why many humans living today show Neanderthal DNA in their genomes. The oldest fossil from which DNA was extracted was an ancient human who lived 400,000 years ago. The DNA sample was extracted from deep in the thigh bone. (C. Zimmer in the New York Times, Dec. 4, 2013; Science, May 7, 2010)