At 1.6 million years old, it survived in the permafrost and identified a new kind of mammoth. But here’s the problem:
Researchers had suspected that ancient DNA could survive beyond one million years, if the right sample could be found. Once an organism dies, its chromosomes shatter into pieces that get shorter over time. Eventually, the DNA strands become so small that — even if they can be extracted — they lose their information content.
Orlando’s team found that fragments as short as 25 DNA letters in their horse bone, from the Canadian Yukon Territory, could still be interpreted. They estimated that million-year-old remains preserved in the constant cold of permafrost — which slows DNA fragmentation — should also contain DNA fragments of that length. “My only doubt: does such a sample exist?” Orlando says…
But thanks to advances in sequencing technology and bioinformatics, his team managed to obtain 49 million base pairs of nuclear DNA from the oldest sample, found near a village called Krestovka, and 884 million base pairs from another tooth, called Adycha. Analysis of the DNA suggested that the Krestovka sample was 1.65 million years old, and the Adycha sample around 1.3 million (see ‘Ancient genomes’). The third sample, a 600,000-year-old woolly mammoth tooth dubbed Chukochya, produced nearly 3.7 billion base pairs of DNA, more than the length of its 3.1-billion-base-pair genome.
Ewen Callaway, “Million-year-old mammoth genomes shatter record for oldest ancient DNA” at Nature
The find re the Krestovka tooth provided evidence for new species arising from hybridization — a concept doubted in the days of full-on Darwinism.
The paper is closed access.
More on the “hybrid” aspect:
In their genetic analysis, Dalén and colleagues also examined how the three ancient mammoths related to other known specimens and species. The Krestovka mammoth, at about 1.2 million years old, came out as a unique lineage of mammoth that didn’t fit into any previously known species. And this newly discovered mammoth lineage had an important role to play. The researchers hypothesize that Mammuthus columbi–a huge species the roamed North America from 10,500 to 1.5 million years ago–originated as a hybrid between the ancestors of the woolly mammoth and the genetic lineage of the Krestovka mammoth. “That certainly came as a complete surprise to us,” Dalén says.
That Mammuthus columbi originated as a new species, born of a hybridization event, “has major implications for our understanding of the population structure of Pleistocene megabeasts,” MacPhee says. The ancestors of the woolly mammoth and the Krestova mammoth had diverged from each other for about a million years before a population produced a hybrid that was different from both, giving rise to Mammuthus columbi. More than that, MacPhee notes, “it suggests that mammoths in the Old and New Worlds acted as a hugely distributed metapopulation,” with populations able to interbreed with each other despite looking different from each other.
Riley Black, “Oldest DNA Sequenced Yet Comes From Million-Year-Old Mammoths” at Smithsonian Magazine
Basically, it doesn’t sound as though we should expect similar DNA finds from the Cretaceous era. Bad news for Jurassic Park.
But we shall see. Many wouldn’t have expected the mammoth DNA.
Better off with mammoths anyhow.