The last free-ranging horses in Europe were hybrids

EDIT: The individual examined in the study is actually the Shatilov tarpan, a specimen which was also caught in the Cherson region but died in 1868. 

The nature of the horses described in contemporaneous literature from previous centuries, such as by Gmelin, Pallas, Smith and others, has long been dubious. It was unclear if those horses were genuine wild horses, feral domestic horses or hybrids. In the Russian steppe, these free-ranging horses of the 18th to the early 20th century were called "tarpans". 

The fact that a black dun colour prevailed in these historic reports may suggest that these horses were at least partly wild horses, because black dun or black was the prevalent colour of late Holocene European wild horses. However, the fact that also non-wildtype colours were mentioned in these reports suggests admixture. The mane of the last free-ranging horse of the Russian steppe was described as being semi-erect, as to be expected from a hybrid between a horse with an upright mane and a falling domestic mane. 

The Cherson Tarpan, photographed in 1884

Librado et al. 2021 examined the genome of the so-called Cherson Tarpan, the only "tarpan" to be photographed. It revealed that at least this individual has a hybrid origin of western wild horses and domestic horses. To be precise, the authors write: "The tarpan horse came about following admixture between horses native to Europe [...] and horses closely related to DOM2". A hybrid origin for the free-ranging horses described in historic references makes sense. That they were pure wild horses was unlikely due to their phenotype (domestic colour variants et cetera). That they were merely feral horses was also unlikely because black dun prevails in these reports, and it would be a big coincidence if feral domestic horses also were mainly black dun in colour. Also, I have always considered it the most likely scenario that the pure wild horse did not die out as a whole but got continuously genetically influenced by feral domestic horses. So it seems that this scenario is confirmed, at least under the assumption that not only the Cherson tarpan but all the other free-ranging horses of Europe during the 18th to 20th century were hybrids. 

The information that the horses historically called "tarpans" might help to stop the inappropriate synonymization of the word "tarpan" with the original European wild horses. 

The study's main purpose was the origin of the domestic horse. They conclude that the domestic horse most likely originated in the lower Volga-Don region, and that mutations on two genes were of particular importance for the domestication of the horse: one on the GSDMC gene, probably improving the horses' ability for bearing weight on their back, and one on the ZFPM1 gene, probably reducing the fear response and increasing the docility of the horses. 

The study, however, completely ignores the work of Taylor et al. 2021 that concluded that the Botai horses were not domestic. 

Literature: 

Librado et al. 2021: The origins and spread of domestic horses from the Western Eurasian steppes. 2021.