Million-Year-Old Mammoth DNA Rewrites Animal's Evolutionary Tree
takyon writes:
Million-year-old mammoth DNA rewrites animal's evolutionary tree
DNA from three ancient molars, one likely to be over a million years old, has revealed that there is a ghost lineage of mammoths that interbred with distant relatives to produce the North American mammoth population.
[...] We don't have precise dates for any of the teeth, as they appear to be too old for carbon dating. Instead, dates have been inferred using a combination of the species present in the deposits and the known timing of flips in the orientation of Earth's magnetic field. In addition, the shape of the teeth provide some hints about what species they group with and provide some further indication of when they were deposited. In all, one tooth is likely to be at least a half-million years old, another about a million years old, and a third somewhat older still.
Previously, the oldest DNA obtained from animal remains is roughly the age of the youngest of these samples. But the researchers were able to recover some elephant-like DNA from each of the molars, although it was badly fragmented, and many individual bases were damaged. Researchers were able to isolate the full mitochondrial genome for each of the three teeth, as each cell contains many copies of this genome in each of its mitochondria. Only fragments of the nuclear genome could be obtained, however-at most, about 10 percent of one genome, and at worst under two percent. (Although less than two percent is still tens of millions of individual bases.)
Using the differences between the mammoth and elephant DNA and assuming a constant rate of mutation, the research team was able to derive independent dates for when each of the animals that left a tooth must have lived. Based on the mitochondria genome, the dates were 1.6 million, 1.3 million, and 900,000 years ago. For the two that had enough nuclear genome to analyze, the dates were 1.3 million and 600,000 years ago. The DNA-based dates for these two lined up nicely with each other and the date of the material they were found in. The oldest sample might be older than the deposit it's in, and thus it might have been moved after death.
Million-year-old DNA sheds light on the genomic history of mammoths (DOI: 10.1038/s41586-021-03224-9) (DX)
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