Scientists have discovered mammoth DNA spanning more than a million years of their evolutionary history. (Image credit: Dottedhippo via Getty Images)
Scientists have identified the oldest woolly mammoth fossil in North America and unlocked its genetic secrets, according to a new study.
A 216,000-year-old tooth has been found along the Old Crow River in Canada's Yukon Territory, confirming that woolly mammoths (Mammuthus primigenius) arrived in North America at least 100,000 years earlier than scientists previously thought.
The study's lead author, Camilo Chacón-Duque, a researcher at the Center for Palaeogenetics at Stockholm University in Sweden, told Live Science via email that the find is unusual because most North American mammoth specimens of this age likely belong to other species that existed before woolly mammoths.
“To our knowledge, the Old Crow mammoth is the oldest North American mammoth fossil that can be confidently morphologically identified as a woolly mammoth,” Chacon-Duque said.
Scientists extracted DNA from the Old Crow mammoth as part of a larger study of mammoth genetics. In the study, researchers identified “long-lost” genetic variations from different mammoth lines over more than a million years of their evolutionary history, according to a report from Stockholm University.
The Old Crow mammoth's DNA was in the oldest group of samples in the analysis, described as “deep DNA,” but it was not the oldest. The oldest DNA, from Russia, dates back about 1.3 million years. The scientists published their results online April 9 in the journal Molecular Biology and Evolution.
The ancestors of mammoths originated in tropical Africa and were closely related to modern elephants. These ancestors later began migrating to the Northern Hemisphere about 3 million years ago, gradually adapting to cold conditions as they spread and diversified.
To study the evolution of mammoths, the researchers analyzed 34 new DNA samples along with data from more than 200 samples presented in previous studies. Chacon-Duque noted that the new samples came from across the Northern Hemisphere, primarily from Siberia and North America.
Mammoth DNA dating
The team extracted and analyzed mitochondrial genomes, or mitogenomes, which are the portion of the genome that resides in a cell's mitochondria and is passed down from mother to offspring. The team then dated the samples using a combination of radiocarbon dating and molecular clock dating, which determines the age of DNA based on gene mutations and the rate at which they change in DNA over time.
Most of the samples were less than 50,000 years old, which is the limit for radiocarbon dating. For older samples, the researchers developed an advanced version of molecular dating to improve its accuracy. Chacon-Duque said they experimented with different setups and parameters for their experiments and found that molecular dating of one sample at a time was more accurate than trying to date multiple samples at once, as some previous studies have done.
“We built on previous methodologies and carefully refined them to obtain more reliable age estimates,” Chacon-Duque added.
Sourse: www.livescience.com
