Already, the new research has shed new light on the evolution of North American mammoths. To the researchers’ surprise, their DNA sequences were so old that they pointed to a time long before the origin of the Mammuthus columbi, the American mammoth, one of the two large mammoth species that once roamed the North American steppes. This provided scientists with new insights into the evolution of these giants.
About a million and a half years ago, descendants of European and Asian steppe mammals had reached North America by crossing the land bridge that now lies beneath the Bering Strait from Siberia. Some time later, this new influx led to the creation of Mammuthus columbi. At least two of the larger mammoth species lived in North America around 100,000 to 200,000 years ago: the woolly mammoth (Mammuthus primigenius) in the north and Mammuthus columbi in more southern regions, as far as Mexico. From previous genetic research, the researchers already knew that American and woolly mammoths mated with each other and that hybrid species had emerged from them.
For a long time, paleontologists used the distinctive upper molars of mammoths to tell the different species apart. Based on fossilized mammoth teeth, they assumed that the mammoth population that lived in North America after one and a half million years ago was American mammoths. But while the fossils found indicate a clear continuity, the genetic material from the new DNA research shows that a major change has occurred.
Two of the mammoth genomes from the new study tie in with the lineage that later produced the woolly mammoth. But the DNA from the oldest of the three molars, nicknamed ‘Krestovka’ by scientists (after the stream where it was found), appeared to belong to a previously unknown lineage that split off from the lineage to which the DNA from the other two members belonged.
When Van der Valk’s team compared the mysterious mammoth genome with the previously sequenced American mammoth genome, they came to an astonishing conclusion: Mammuthus columbi is a hybrid that arose between 400,000 and 500,000 years ago after a cross between Krestovka mammoths and Siberian woolly mammoths – a cross that must have occurred somewhere in Siberia, North America or Beringia (the land bridge between the two regions).
After a second crossing that took place in North America some 200,000 years ago, took Mammuthus columbi another 11 to 13 percent of its woolly mammoth genome remains. By the time the American mammoth became extinct some 12,000 years ago, about three-fifths of its total genome could be traced to the woolly mammoth, while the remaining two-fifths came from the enigmatic Krestovka mammoth, known only from DNA from a single molar.
The research shows how well (and how long ago) mammoth species adapted to the cold climate. Previous research on ancient DNA had already revealed the genetic details of this adaptation to the cold by woolly mammoths. But many of the gene variants responsible for woolly mammoths’ ability to weather the bitter cold first showed up in much older mammoth species. And the new research now shows that more than 85 percent of these variants in the woolly mammoth were present over a million years earlier in the steppe mammoths of Siberia, the distant ancestors of the woolly mammoth.
Fossil finds have shown that mammoths lived in the far north as far back as one million years ago, so it’s not surprising that these Nordic titans were so resistant to the cold. But the new study now offers a unique glimpse into the speed with which this adaptation process to the cold went. Mammoths seem to have developed their ‘cold genes’ at a more or less steady pace, not in short evolutionary sprints.
Details in the DNA
According to paleontologists, the discovery will Mammuthus columbi hybrid, further contributing to the ongoing reappraisal of the fossils found of North American mammoths to date.
Recent research comparing fossils of mammoth teeth with the family trees of North American mammoth species had already shown that the different shapes of these teeth are far from a direct reference to the various mammoth species, but that they overlap by region across North America. . Article link https://www.news1.news/news/2021/02/the-worlds-oldest-dna-isolated-from-ancient-mammoth-molars.html
The new study emphasizes that fact once more: before and after 500,000 years ago, there are no significant changes in the teeth of North American mammoths, while the genetic changes that indicate Mammuthus columbi was immense.
“Without genetics, we would be looking at morphology, that is, changes in shape, and without those changes in shape, we couldn’t see changes in a species,” said Lindsey Yann, a paleontologist at Waco Mammoth National Monument in Texas. “When you add the genetic component, you can really tell things apart, and we now have the data to demonstrate that.”
For co-author Adrian Lister, paleontologist at the Natural History Museum in London and one of the foremost mammoth experts in the world, the new research also highlights a long-drawn-out question: how should the teeth of North American mammoths be classified when there is no DNA? is available? If Mammuthus columbi Genetically only emerging around 400,000 to 500,000 years ago, how should paleontologists interpret older mammoth teeth that look exactly the same? Until now, no one has published a study on DNA from North American mammoth teeth older than half a million years.
To add more pieces to the puzzle, Dalén and his colleagues plan to apply their spectacular skills to North American mammoth teeth as well. Article link https://www.news1.news/news/2021/02/the-worlds-oldest-dna-isolated-from-ancient-mammoth-molars.html
The team has already identified some potential candidates for future sequencing: a 500,000-year-old mammoth tooth from Canada and a 200,000-year-old tooth believed to belong to a woolly mammoth.
Now that the scientists have broken the one-million-year mark, it is only a matter of time before even older DNA will reveal its secrets. “That’s the next big goal,” says Dalén. “We’ve seen the data we could produce and I think it will be relatively easy to go back more than two million years if we have a suitable fossil.”
This article was originally published in English on NationalGeographic.com
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