A wild Przewalski’s horse. Probably close to how ancient wild horses looked.
I was looking up this subject in relation to the wheel. I found this article:
Soil from a Copper Age site in northern Kazakhstan has yielded new evidence for domesticated horses up to 5,600 years ago. The discovery, consisting of phosphorus-enriched soils inside what appear to be the remains of horse corrals beside pit houses, matches what would be expected from Earth once enriched by horse manure. The Krasnyi Yar site was inhabited by people of the Botai culture of the Eurasian Steppe, who relied heavily on horses for food, tools, and transport.
“There’s very little direct evidence of horse domestication,” says Sandra Olsen, an archaeologist and horse domestication researcher at the Carnegie Museum of Natural History in Pittsburgh, PA. That’s because 5,600 years ago there were no saddles or metal bits to leave behind. Equipment like bridles, leads, and hobbles would have been made from thongs of horse hide, and would have rotted away long ago. Likewise horses themselves have not changed much physically as a result of domestication, unlike dogs or cattle. So ancient horse bones don’t easily reveal the secrets of domestication.
With research funding from the National Science Foundation, Olsen’s team took a different tack. They looked for circumstantial evidence that people were keeping horses. One approach was to survey the Krasnyi Yar site with instruments to map out subtle electrical and magnetic irregularities in the soils. With this they were able to identify the locations of 54 pit houses and dozens of post moulds where vertical posts once stood. Some of the post moulds were arranged circularly, as would be most practical for a corral.
Next, geologist Michael Rosenmeier from the University of Pittsburgh collected soil samples from inside the fenced area and outside the settlement. The samples were analyzed for nitrogen, phosphorus, potassium, and sodium concentrations by Rosemary Capo, University of Pittsburgh geochemist, and her students. Modern horse manure is rich in phosphorous, potassium, and especially nitrogen, compared to undisturbed soils. But because nitrogen is mobile in soils, it can be lost to groundwater or transferred to the atmosphere by organic and inorganic processes. Phosphorus, on the other hand, can be locked into place by calcium and iron and is more likely to be preserved in the soils for millennia.
As it turned out, the soil from inside the alleged corral had up to ten times the phosphorus concentration as the soils from outside the settlement. Lots of phosphorus can also indicate a hearth, said Capo, but that phosphorus is usually accompanied by a lot of potassium, which is not the case in the corral at Krasnyi Yar.
The corral soils also had low nitrogen concentrations, says Capo, reducing the likelihood that the phosphorus came from more recent manure. “That’s good, actually,” she said of the recently completed nitrogen analyses. “It suggests we’ve got old stuff.”
I had a nose about on line, and the same team also want to analyse pottery for the remains of mares milk, which would confirm domestication.
While on this subject I found mt DNA study that suggests the horse was domesticated in multiple locations; Asia, Europe and Iberia/NW Africa.
The place and date of the domestication of the horse has long been a matter for debate among archaeologists. To determine whether horses were domesticated from one or several ancestral horse populations, we sequenced the mitochondrial D-loop for 318 horses from 25 oriental and European breeds, including American mustangs. Adding these sequences to previously published data, the total comes to 652, the largest currently available database. From these sequences, a phylogenetic network was constructed that showed that most of the 93 different mitochondrial (mt)DNA types grouped into 17 distinct phylogenetic clusters. Several of the clusters correspond to breeds and/or geographic areas, notably cluster A2, which is specific to Przewalski’s horses, cluster C1, which is distinctive for northern European ponies, and cluster D1, which is well represented in Iberian and northwest African breeds. A consideration of the horse mtDNA mutation rate together with the archaeological time frame for domestication requires at least 77 successfully breeding mares recruited from the wild. The extensive genetic diversity of these 77 ancestral mares leads us to conclude that several distinct horse populations were involved in the domestication of the horse.