What name use for ‘Horses’?
E. ferus. Whatever was the ‘Tarpan’, its presently available osteological remains are limited to one complete skeleton (St Petersburg : ZIN 521) and one isolated slull without mandible (Moscow : MGU 94535). Moreover, both Tarpans were old and castrated. Other specimens labelled ‘tarpans’ are the result of tentative genetic reconstructions by crossing domestic horses and selecting which individuals appear, in their exterior morphology, more like the available descriptions of extinct Tarpans. The Pleistocene fossil wild horses differ markedly from the known Tarpan remains. For these reasons, I do not think appropriate to use the latin name of the Tarpan – Equus ferus – for all wild caballine horses.
E. caballus being the name of the domestic form, it does not seem appropriate either. Moreover, I feel that to apply a single specific name to animals whose ranges in space (a) and time (b) are so extensive is not a good solution : do they really belong to a single species? After all, the degree of genetic proximity between the mongolian wild Prjewalsi’s horse and the domestic forms is not clear (Ryder 1994),
One thing is clear, however : the existence of a group of horses, wild and domestic, extant and fossil, which share some associated cranial and dental characters, and which can be united under the name of ‘Caballines’. I insist on the association of characters necessary to define this group (as well as others groups indeed) : a single character may be shared by diverse species or groups of species.
Now, how can we refer to representatives of this ‘Caballine’ group ? And what is the status of the Caballine group, a subgenus? or a species? And what is the status of the diverses forms within, are they subspecies? or simple morphs? In any of these cases, we should ‘formally’ name the horse from Mosbach (for example) either Equus caballus mosbachensis or Equus ferus mosbachensis. If (as it happened) a subspecies was recognized, its name should be Equus caballus mosbachensis lunellensis.
I prefer to avoid this quadrinomial nomenclature, and (with appropriate apologies to the formal Taxonomy…) will use a binomial one : Equus mosbachensis, and specify that this animal belonged to the Caballine group.
[(a) In the Old World, during the late Pleistocene, caballine horses may be found from 75°N (Lazarev 1980) to 35°N (Bagtache et al. 1984), and from 130°E (Kuzmina 1990) to 10°W (Cardoso 1996). At the same period, caballine horses were present in North America from Alaska and Yukon to California and Louisiana.
(b) Members of a single species are supposed to be recognized, not according to their resemblances, but according to their ability to produce fertile offspring. Naturally we cannot use genetic criteria in paleontology, but even in zoology, the answer to a conspecificity issue is not always a plain ‘yes’ or ‘no’. Note that for the domestic horses, at least 77 DNA types were found among the extant populations, and were probably already present 10,000 years ago (Oakenfull and al. 2000).]