The mitochondrial genome of a Pleistocene cave bear (Ursus deningeri) has been reconstructed using extremely short DNA molecules from a bone that is more than 300,000 years old. Apart from rare specimens preserved in permafrost, the fossil is some 200,000 years older than any other material used to generate a complete DNA sequence.

By reworking methods to purify the tiny amounts of damaged DNA that are typical of old samples, Jesse Dabney at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and his colleagues collected and sequenced DNA strands as short as 30 basepairs. More than 90% of the sequences used to produce the genome were less than 50 basepairs long — too short to be used efficiently with conventional methods.

The technique could allow researchers to recover DNA from ancient humans and other specimens that are currently considered too degraded for most analyses.

Proc. Natl Acad. Sci. USA (2013)