The species of the aurochs, Bos primigenius, has many synonyms – last time I counted it was 8, counting only those that are based on wildtype material and there might be more (with those based on cattle there would be much more). One of those synonyms is Bos trochoceros, a species which was described for Pleistocene European aurochs. However, as the differences between Pleistocene European aurochs and Holocene European aurochs is not dramatic enough to justify a split on species level, it has been synonymized decades ago. But what about subspecies level? Might it be justified to classify Pleistocene European aurochs as Bos primigenius trochoceros?
There were differences in the morphology of Pleistocene and Holocene European aurochs. First of all, the former reached very large sizes of 200 cm withers height or more, while individuals from the Middle and Late Holocene were smaller (what was most likely due to anthropogenic factors). It also had – on average – considerably larger and more wide-ranging horns as the horn size of Holocene aurochs was decreasing and also the curvature was narrower (with large-horned Holocene individuals such as the Sassenberg bull being exceptions) throughout this period. The coat colour, however, was seemingly identical between Pleistocene and Holocene European aurochs, as a comparison between cave paintings and historic texts suggest. The question if the differences in body size and horn size are enough for a split on subspecies level is not easy to answer, as taxonomy is rather subjective – what is distinct enough for one worker is not distinct enough for the other.
However, genetic information might endorse a split on subspecies level. Southern European aurochs (at least Italian ones) have the mitochondrial haplotype T which is also found in taurine cattle (hence the “T”), while those from the Northern half of Europe have the haplotype P (from “primigenius”). Southern Europe was a refuge for the aurochs during the last glacial, when the mammoth steppe covered most of its former range in Europe. The different haplotype of northern aurochs suggest that Europe was recolonized from the East rather than from the South after the last glacial [1]. So, there is a genetic difference between Southern and Northern European aurochs, and it must be noted that during the Pleistocene the range was restricted to Southern Europe. 
A Pleistocene aurochs skull from Germany with massive and wide-ranging horns - Bos primigenius trochoceros?
As it happens, Bos trochoceros is based on a Pleistocene skull from Siena, Italy [2]. And Bos primigenius is based on a Holocene skeleton from Haßleben in Germany, thus the northern half of Europe. Doesn’t that fit nicely? So, can we say that Bos primigenius primigenius represents only the Central and Northern European aurochs from the Holocene, that migrated from the East to Europe after the last glacial and have the P haplotpye, and that Bos primigenius trochocerosrepresents the Southern European aurochs that were slightly larger, had larger and more wide-ranging horns, were present in Europe during the last glacial and all had the T haplotype? I don’t consider this assumption all too absurd. We also have to consider that there likely was a continuum between both forms, as their range was continuous during the Holocene (similar as in the case of Canis lupus lupus and Canis lupus italicus). Not all Holocene aurochs with the P haplotype had smaller horns (see the Sassenberg specimen) and not all of them were smaller than Pleistocene Southern European ones (see the Prejlerup specimen which might have been around 195 cm tall in life).
It seems that I am not the only one who considers the use of the trinominal name Bos primigenius trochoceros legitimate. The name has been used in a 2020 paper and a 1995 work for Middle Pleistocene aurochs remains in France [3,4].
If a split on subspecies level within the European aurochs was legitimate, this also would have consequences for the evolution of cattle. Since Southern European aurochs have the T haplotype, Near Eastern aurochs in the fertile crescent from 10.000 years ago that were the ancestors of taurine cattle, likely had the same haplotype. Quite possibly, the populations were connected at some point, and most likely the aurochs entered Southern Europe via Anatolia. Therefore, it is likely that Near Eastern aurochs from that time can be or must be considered Bos primigenius trochoceros too. That means taurine cattle were not domesticated from the nominate subspecies, Bos primigenius primigenius. Nevertheless, B. p. primigenius in this strict sense left a lot of living descendants because of secondary introgression into cattle in Europe (go here).
I consider this split on subspecies level at least possible – I am very open for the possibility that trochoceros rises from the grave of the junior synonyms thanks to genetic and morphological information. We would have five mainland subspecies of the aurochs in this case: the Northern European aurochs Bos primigenius primigenius, the Southern European (and possibly Near Eastern) aurochs Bos primigenius trochoceros, the North African aurochs Bos primigenius mauretanicus, the Indian aurochs Bos primigenius namadicus, and the East-Asian aurochs Bos primigenius suxianensis. I am also convinced that this would not be over-splitting as other bovines with a large geographical range such as the cape buffalo which is divided into two to three subspecies (depending on the status of Syncerus nanus), and this includes only those that live today in the late Holocene. The aurochs simply was a species with a large geographical range over a comparably long period of time, which goes hand in hand with the evolution of several subtypes.
Literature
[1] Mona et al.: Population dynamic of the extinct European aurochs: genetic evidence from a north-south differentiation pattern and no evidence of post-glacial expansion. 2010.
[2] Rütimeyer: Überreste von Büffeln (Bubalus) aus den quaternären Ablagerungen von Europa. 1870.
[3] Uzunidis: Dental wear analyses of Middle Pleistocene site of Lunel-Viel (Herault, France): did Equus and Bos live in a wetland? 2020.
[4] Tuffreau et al.: Le gisement acheuleen de cagny-l’epinette (somme). 1995.
I think the most appropriate term for this kind of thing would be "chronotype". The concept already exists for American bison. There are numerous forms, progressing from priscus and latifrons to antiquus and occidentalis and finally to the modern bison. Really all of these should be regarded as a range of forms within a single species, which I would dub Bos bison, but having names to describe these eco/chronotypes can be useful.
ReplyDeleteThat's certainly possible, that would also depend on if the aurochs that inhabited Europe during the last interglacial and retreated southwards during the last glacial were ancestral to those that inhabited Europe during the Holocene, and which haplotype the middle Pleistocene aurochs in Europe had. Mona et al. suggested that the P haplotype evolved somewhere in the East, what would mean that the aurochs of the last Interglacial were probably not ancestral to those that inhabited the northern half of Europe during the Holocene.
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