Horses and humans in North America: Another piece added to puzzle

The horse jaw specimen is dated at 19,650 radiocarbon years, which is equivalent to between 23,000 and 24,000 calendar years ago. The bone surface is a bit weathered and altered by root etching but the cut marks are well preserved; they are located on the side, under the third and second molars, and are believed to be associated with the removal of the tongue using a stone tool.
The horse jaw specimen is dated at 19,650 radiocarbon years, which is equivalent to between 23,000 and 24,000 calendar years ago. The bone surface is a bit weathered and altered by root etching but the cut marks are well preserved; they are located on the side, under the third and second molars, and are believed to be associated with the removal of the tongue using a stone tool. Image: PLOS ONE study

One of the intriguing questions in the rich ancient history of the horse centers around its demise in North America.

It is fascinating because we don’t have a complete picture of what led to their disappearance several thousand years ago, although there is evidence that climate change and associated vegetation changes played a crucial role.

What adds an element of mystery is the role of man, if any, in their demise. Is it possible that the arrival of humans on the continent played a part?

The weight of scientific opinion lies with climate and vegetation changes being behind the decline, but there is a growing body of evidence which has been pushing the human-horse overlap out to several thousand years.

There is now evidence that horses lingered in parts of the continent longer than 12,500 years ago, which seemed to be a figure that attracted some agreement within the scientific community.

Today, we have evidence of the horse’s survival in a pocket of North America until 7600 years ago – some 5000 years longer than previously thought. Researchers who removed ancient DNA from horse and mammoth remains in permanently frozen soil in central Alaskan permafrost dated the material at between 7600 and 10,500 years old.

The new timeline from the 2009 research suggested an overlap with human habitation approaching 6000 years.

I’ve followed all the arguments around the fate of the horse in North America with interest.

Some consider the species, having been reintroduced by the Spanish conquistadors, to be feral in North America. Others argue that its absence from the continent for a few thousand years in the context of millions of years of habitation is neither here nor there. The species, even acknowledging its reintroduction, should be considered native.

Some believe that horses never died out at all.

For me, the area of greatest interest lies in the mists of time, when humans were getting established on the continent and horses were already in trouble, with dwindling numbers pushing them close to extinction.

The evidence is now clear that humans butchered horses. A cache comprising 83 stone implements found within the city limits of Boulder City, Colorado, in 2008 provided scientists with invaluable insights.

Biochemical analysis showed that some of the 13,000-year-old implements were used to butcher ice-age camels and horses.

The University of Colorado study was the first to identify protein residue from extinct camels on North American stone tools and only the second to identify horse protein residue on a Clovis-age tool. A third tool tested positive for sheep and a fourth for bear.

Other evidence of early Americans hunting horses had earlier been uncovered by University of Calgary scientists, who discovered the remains of a pony-sized horse while excavating the dry bed of the St Mary Reservoir in southern Alberta.

Several of the horse’s vertebrae were smashed and it had what appeared to be butcher marks on several bones. About 500 metres from the skeleton, they found several Clovis spearheads. Protein residue testing and examination confirmed they had been used to hunt horse.

Now, we have some tremendous research that redraws an important part of the picture.

Evidence has been uncovered of horse butchery in North America that dates back 24,000 years. The groundbreaking study pushes the timing of the first entry of humans into North America across the Bering Strait back by 10,000 years.

A horse mandible from the Yukon shows the marks of a stone tool apparently used to remove the tongue. The jaw was dated at 19,650 radiocarbon years – the equivalent to between 23,000 and 24,000 calendar years ago.

The work by University of Montreal anthropology professor Ariane Burke and her doctoral student Lauriane Bourgeon, as well as the efforts of Dr Thomas Higham, who is deputy director of Oxford University’s Radiocarbon Accelerator Unit, involved painstaking analysis of artifacts removed from the Bluefish Caves, on the banks of the Bluefish River in northern Yukon, not far from the Alaska border.

Although the caves yielded a massive haul of animal bones from the likes of horses, mammoth, bison and caribou, there was no evidence that this accumulation arose from human activity.

Bourgeon examined about 36,000 bone fragments taken from the caves in a task that took her two years.

Certain bone pieces were taken to the University of Montreal’s Ecomorphology and Paleoanthropology Laboratory, where further work revealed undeniable traces of human activity in 15 bones. About 20 other fragments showed probable traces of the same type of activity.

Burke says a series of straight, v-shaped lines on bone surfaces were made by stone tools used to skin animals. “These are indisputable cut-marks created by humans,” she says.

Bourgeon organized further radiocarbon dating of the specimens.

The oldest fragment, a horse jaw showing marks from a stone tool, was dated to between 23,000 and 24,000 years ago.

The different activities on the bones included skinning, dismembering and defleshing.

“Our discovery confirms previous analyses and demonstrates that this is the earliest known site of human settlement in Canada,” Burke says. “It shows that Eastern Beringia was inhabited during the last ice age.”

Beringia is a vast region stretching from the Mackenzie River in the Northwest Territories to the Lena River in Russia.

But, as always, the picture is complicated. Just because humans were living in the region 24,000 years ago did not mean they immediately set off across the continent.

Indeed, studies in population genetics have shown that a group of a few thousand individuals lived in isolation from the rest of the world in this region 15,000 to 24,000 years ago. This is known as the Beringian standstill, or genetic isolation, hypothesis.

The terrain was too challenging – there were glaciers and rugged steppes – and perhaps tough living conditions didn’t provide the opportunities to look further afield.

Research such as this makes a tremendous contribution to the picture of early North American habitation and adds to our knowledge on the fate of the megafauna that once roamed the continent.

We are still a long way from the full picture, but it’s fascinating to watch the pieces of the puzzle fall into place.

Further reading:

Why did horses die out in North America? 

Evidence of horse hunting in North America pushed back to nearly 24,000 years ago 

The latest study can be read here

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