AINEWS
700,000-year-old poop reveals a lost Ice Age world
A 700,000 year old pellet from a permafrost sealed squirrel burrow in Yukon has yielded DNA from woolly mammoths, an ancient cheetah lineage, and dozens of other Ice Age species.
A 700,000 year old pellet from a permafrost sealed squirrel burrow in Yukon has yielded DNA from woolly mammoths, an ancient cheetah lineage, and dozens of other Ice Age species.
A pea-sized pellet, expelled by an Arctic ground squirrel roughly 700,000 years ago and pried from a permafrost-sealed burrow in Yukon, has yielded DNA from woolly mammoths, an ancient cheetah lineage, and dozens of other plants and microbes, according to research published in Nature Communications (McMaster University press release).
Coprolites — the polite name for fossilized feces — have long been the underdogs of ancient DNA research. They are fragile, smelly, and quickly broken down by microbes, so the genetic material inside them rarely survives long enough to be sequenced. The Yukon pellets survived because Arctic ground squirrels dug deep burrows that froze and stayed frozen, sealing each deposit in permafrost for hundreds of thousands of years.
The team rebuilt at least 18 mitochondrial genomes — the small, maternally inherited packets of DNA used to identify which species a fragment came from — from a single class of object, the paper reports. The haul includes woolly mammoths (Mammuthus primigenius), an American cheetah (Miracinonyx trumani),[1] and a mix of plants and microbes that paints a picture of a community in the vanished land-bridge region of Beringia that once joined Siberia and Alaska.
The 700,000-year date comes from the Gold Run tephra layer associated with the oldest sample, dated to 688,000 ± 44,000 years ago using uranium-lead radiometric dating.[2] The younger samples span 30,000 to 80,000 years ago.
The technique is reproducible: any team with access to permafrost burrows can now treat squirrel pellets as ancient environmental DNA repositories. That matters because the same warming that exposes these burrows is also destroying them. The window for pulling more of these time capsules out of the ground is closing with the permafrost itself.
[1] Miracinonyx trumani, the American cheetah, is a distinct species from the modern African cheetah (Acinonyx jubatus) and is thought to have been a pursuit predator of pronghorn antelope on the North American steppe.
[2] Uranium-lead dating of volcanic tephra is a radiometric method suitable for samples beyond the ~50,000-year limit of radiocarbon dating.