I don't think that analysis is right. From the original Royal Society paper: > The average DNA half-life within this geographically constrained fossil assembla

I don't think that analysis is right. From the original Royal Society paper: > The average DNA half-life within this geographically constrained fossil assemblage was estimated to be 521 years for a 242 bp mtDNA sequence, corresponding to a per nucleotide fragmentation rate (k) of 5.50 × 10–6 per year. If there is a 50% chance that a 242 base pair sequence has a break in 500 years, you will be able to recover the full sequence in way more than 50% of 500 year old samples. First, you have many copies of the same DNA fragment in a macroscopic drop of blood, so some will not have a break. Second, even if it's older and all strands have at least one break, you can look at a bunch of half strands or tenth strands and infer the complete sequence. Likewise, if I had a thousand copies of a book where each copy had a few destroyed pages, it would not be hard to reconstitute the entire contents of the books. I think the above rate of decay would allow for recovery of the sequence in a sample after probably tens of thousands of years. This is why mammoths, but not dinosaurs, are typically the targets for brining back extinct mammals.