The oldest DNA recovered from an animal is adding new chapters to the life history of mammoths, dating back more than 1 million years.
The genetic material of ancient mammoth molars found in Siberia beats very well the previous record set by 700,000-year-old DNA of a frozen and fossilized horse (SN: 26/6/13). Some fragments of mammoth genes suggest that ancient mammoths already had traits that allowed them to withstand cold temperatures during the last ice ages. What’s more, some furry monsters that inhabited North America may have been a hybrid mix between the woolly mammoth and a previously unknown mammoth species, researchers reported Feb. 17 in Nature.
The findings “really highlight the exciting times we live in,” says Charlotte Lindqvist, an evolutionary biologist at Buffalo University in New York who didn’t participate in the work. "We can get genetic data (we can retrieve DNA) from samples so old that they can give us windows directly into the past." These data may reveal how extinct animals evolved, adding to the clues that come from physically examining ancient bones.
Mammoth DNA was extracted from three molars unearthed in the 1970s from permafrost in northern Siberia. Although DNA degrades into shorter strands of genetic material over time, making it difficult to handle and put together, cold permafrost helps protect genetic information from rapid fall. Theoretical studies have suggested that researchers could recover DNA more than 1 million years old. Still, the recovered DNA is “pretty close to the limit of what’s possible,” says Love Dalén, an evolutionary geneticist at the Stockholm Center for Paleogenetics.
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The two oldest specimens, named Krestovka and Adycha, lived between 1.2 and 1 million years ago, Dalén and colleagues found. The third, called Chukochya, dates from 800,000 to 500,000 years ago. Genetic analyzes of the ancient DNA recovered from these specimens, as well as the DNA of other mammoths and current elephants, suggest that Krestovka and Adycha belonged to two different mammoth species. Researchers had previously thought that only one type of mammoth, called the steppe mammoth (Mammuthus trogontherii), lived in Siberia 1 million years ago.
Although Adycha was part of the lineage of steppe mammoths that eventually gave rise to woolly mammoths, the Krestovka mammoth may have diverged from its relatives more than 2 million years ago and could represent an unknown line of mammoths, the researchers found. That unidentified species could have mixed with woolly mammoths to give rise to the Colombian mammoth (M. columbi) – which roamed North America – at least 420,000 years ago. The youngest Chukochya may have been an early woolly mammoth (M. primigenius).
The study adds to the amount of genetic material the researchers decoded and expanded the geographic range where those mammoth samples came from, says Vincent Lynch, an evolutionary biologist at the University at Buffalo who did not participate in the work. Analyzing the genetics of many mammoths from different places is “important if you want to make statements about how mammoths were mammoths, why they look like they are, and how diverse they were,” Lynch says.
The team found traits such as hairy hair, which probably helped the mammoths cope with the cold. (SN: 7/2/15). The mammoths of Adycha and Chukochya already had the genetic adjustments of many of these traits, implying that furry animals have slowly adapted to the cold of the ice ages over hundreds of thousands of years. “A lot of the mutations we think make mammoths mammoths (small ears, a lot of fat, not sensitive to cold) occurred before they got into that environment,” Lynch says.
Still, while the new results are intriguing, old DNA is fragile and there is a limit to the amount of data researchers can get from old specimens, Lindqvist says. Therefore, the findings are unlikely to be the full story, she says.