An rbcL sequence from a Miocene Taxodium (bald cypress).

During the past decade, ancient DNAs from both animals and plants have been successfully extracted and analyzed. Recently, the age of DNA that can be recovered and sequenced was increased manyfold by the amplification and sequencing of a DNA fragment from a Magnolia fossil obtained from the Miocene Clarkia deposit (17-20 million yr old). However, the validity of this report has been questioned based on models predicting that DNA should be completely degraded after 4 million yr. We report here the successful amplification, sequencing, and analysis of a 1320-base-pair portion of the chloroplast gene rbcL from a Miocene Taxodium specimen, also from the Clarkia site. These data not only validate the earlier report of sequence data for a Magnolia species from the same site but also suggest that it may be possible to isolate and sequence DNAs routinely from the Clarkia deposit. The ability to recover and sequence DNAs of such age offers enormous research possibilities in the areas of molecular evolution, biogeography, and systematics.

Chloroplast DNA sequence from a miocene Magnolia species.

DNA has been successfully extracted from several samples of preserved tissue, the oldest so far reported originating from a 13,000-year-old ground sloth. Both severe damage to the preserved DNA, primarily due to oxidation of the pyrimidines, has prevented the acquisition of sequence data from ancient samples except in a few cases. We report here the extraction of DNA from fossil leaf samples from the Miocene Clarkia deposit (17-20 Myr old), the amplification of an 820-base pair (bp) DNA fragment from the chloroplast gene rbcL from a fossil of the genus Magnolia, and its subsequent sequencing. The sequence was verified by comparison with published and unpublished rbcL sequences. These results extend our ability to analyse ancient DNA and may open new avenues into problems in palaeobotany, biogeography, and in the calibration of mutation rates.