was made possible because the bone was found preserved in Canadian permafrost following the animal’s demise.
The study also suggested that the ancestor of all equines existed around four million years ago.
A remnant of the long bone of an ancient horse was recovered from the Thistle Creek site, located in the west-central Yukon Territory of Canada.
Palaeontologists estimated that the horse had last roamed the region sometime between a half to three-quarters of a million years ago.
An initial analysis of the bone showed that despite previous periods of thawing during inter-glacial warm periods, it still harboured biological materials – connective tissue and blood-clotting proteins – that are normally absent from this type of ancient material.
And this finding was significant as study co-author of the paper, Dr Ludovic Orlando from the University of Copenhagen, explained to the BBC World Service programme Science in Action.
“We were really excited because it meant that the preservation was really good,” he told the BBC. …
From the resulting equine DNA fragments, they reconstructed a draft of its genome. Although the derived sequence data only covered around 70% of the entire genome, this was sufficient foundation for some revealing analyses.
The tell-tale presence of Y chromosome markers showed that the Thistle Creek bone had belonged to a male.
But the DNA also enabled them to reconstruct the evolutionary history of the larger Equus genus, which includes modern-day horses and zebras.
To do this, the scientists also determined the DNA sequence of a donkey, an ancient pre-domestication horse dating back around 43,000 years, five modern horses and a Przewalski’s horse, which possibly represents the last surviving truly wild horse population.
Family trees, based on similarity of the DNA sequences, revealed the relationships between these equine stable-mates and their longer evolutionary history.
Heirs and grazes
The Thistle Creek genome was reassuringly ancestral to the modern horses – positioned as it was at the base of the tree.
Geological dating evidence meant that the researchers could calibrate the rate of evolution in the different branches, and from this look back into the depths of the tree to approximate the age of the Equus genus ancestor – the forerunner to the donkey, zebra and horse.
Horse bone fragments DNA was extracted from pieces of the ancient bone
The results suggested it grazed the grasslands between 4 and 4.5 million years ago – twice as long ago as most previous estimates. …
Over the last two million years horses had experienced significant population expansions and collapses associated with climatic changes, and one collapse coincided with the date when the Thistle Creek and modern horses diverged. …
But would we recognise the Equus ancestor as a horse?
“Even if you look at the Przewalski horse, which has a divergence time of only about 50,000 years ago… and compare it to the domestic horse, you can already see differences,” observed Prof Willerslev.
“I would definitely say it would not look like a horse as we know it… but we would expect it to be a one-toed horse.”