Ancient Yukon fossil changes scientific thinking

Listen The discovery of semi-fossilized bones in Canada’s far north has geneticists and indeed much of the scientific world excited.

It is known that DNA can survive long after the organism dies, even many thousands of years in the right conditions.  However these are almost never complete but rather as short broken pieces of the chromosome. Sometimes though enough pieces can be  assembled to recreate the complete genome.

Previously, the limit for being able to find enough DNA bits and pieces to recreate a genome was thought to be about 70,000 years. This discovery of ancient horse bones by Duane Froese and his team has led to a major reassessment of previously held beliefs.

The horse bones which were found in permafrost in the Yukon and Klondike were, determined to be about 700-thousand years old and were so well preserved by the permafrost that, combined with recent technology, they were able to sequence the genome and develop new information  about horse evolution.

Duane Froese is a professor of Geology in Earth and Atmospheric Sciences at the University of Alberta and Canada Research Chair in Northern Environmental Change

When the bones were first discovered, the large size was of immediate interest as was the excellent state of preservation. Usually ancient horse fossils from the unglaciated areas of the Yukon, Alaska and Siberia date to the last 100-thousand years, and show much smaller animals.  Dr Froese has seen bones of much larger horses at geologically older sites, but because these had lain frozen in the permafrost for hundreds of thousand of years, they were in far better condition.

Because of the low-moisture, low oxygen level of the permafrost where they had lain, the bones had not become fossilized, theDNA had not been completely destroyed, and even collogen was present.

By sequencing this ancient horse genome and comparing it with those of a 43,000 year old horse genome, several modern horses and a donkey, they have now revised previously held beliefs about when horse species split into various branches of zebras, horses, and donkey. The new information pushes back the split in time to almost double at 4 to 4.5 million years ago.

The new research also shows that there have been major fluctuations in horse populations in conjunction with climatic changes, including major losses in diversity.

The new genome work also is good news for those who have been preserving the  Przewalski’s Horse of the Mongolian steppe. Discovered by western researchers in the latter half of the 19^th century, the evolutionary origin of this horse, that shows striking physical differences compared to domesticated horses, as well as an extra-pair of chromosomes, remained a mystery.  The new effort shows this species was isolated from modern horses about 50,000 years ago.  There had long been concerns that the horse had however been mixing with domestic horses. The genome shows there are pure strains of the species and is worthy of the conservation efforts.

Dr Froese notes that as technology advances more and better genetic data will become available leading to a better understanding of what drives evolution and the roles of things like climate change.

The report on the findings will be published in the July 4 edition of the scientific journal, Nature.

U of Alberta, Duane Froese page

Froese Group

CANQUA-CGRG Edmonton  Aug 18-22, 2013