Genetic scientists have sequenced and analyzed short pieces of DNA preserved in bones from an early Middle Pleistocene horse that had been kept frozen for the last 700,000 years in permafrost at Thistle Creek, Yukon, Canada.
Unlike the small Ice Age horse fossils that are common across the unglaciated areas of the Yukon, Alaska and Siberia that date to the last 100,000 years, the Thistle Creek horse fossil found by Dr. Duane Froese from the University of Alberta was at least the size of a modern horse.
The scientists had dated the permafrost at the site from volcanic ashes in the deposits and knew that it was about 700,000 years old – representing some of the oldest known ice in the northern hemisphere. They also knew the fossil was similarly old.
They them extracted collagen from the fossil and found it had preserved blood proteins and that short fragments of ancient DNA were present within the bone.
The DNA showed that the horse fell outside the diversity of all modern and ancient horse DNA ever sequenced consistent with its geologic age. After several years of work, a draft genome of the horse was assembled and is providing new insight into the evolution of horses.
The study, reported in the journal Nature, showed that the horse fell within a line that includes all modern horses and the last remaining truly wild horses, the Przewalski’s Horse from the Mongolian steppes.
The 700,000-year-old horse genome – along with the genome of a 43,000-year-old horse Equus lambei, six present-day horses and a donkey – has allowed the team to estimate how fast mutations accumulate through time. In addition, the new genomes revealed episodes of severe demographic fluctuations in horse populations in phase with major climatic changes.