Two zebus with traits of the Indian aurochs

At first glance, zebus seem to be rather different from the aurochs. But there are certain traits found in many zebus that are very reminiscent of the wildtype. For example, many zebu landraces from South Asia have a very short trunk with long legs (more so than most taurine breeds on this world) and small udders. Many also have a comparably long snout. Surely, their often hanging ears, the fleshy hump (which is less likely to be a wildtype trait than a trait that appeared after domestication) and the often rather derived horn shapes give them an unusual appearance that creates the impression they are more removed from the aurochs than taurine breeds, but the huge udders, the piebald colour and tiny horns of Holstein-Frisian, for example, are not wildtype traits either. And not to forget, zebus have been found to share alleles with the European aurochs that taurine cattle have lost [1]. It is most parsimonious to assume that these alleles were also present in the Indian aurochs. Thus, zebus are actually more "primitive" than their looks suggest at first glance. 

While searching for zebus with wildtype traits I found photos of one living zebu and one skull that both respectively share traits with Bos primigenius namadicus. 

For the living individual, go here and here. It has a crazily extreme primigenius spiral. And as so often when a domestic cattle individual has a perfect primigenius spiral, it is a steer (the picture description on shutterstock says it is an ox, thus castrated). Nevertheless, the horns are interesting. Not only because of their curvature, but also because they are antero-posteriorly compressed on the proximal half and thus oval in cross section, which was a trait of B. p. namadicus. In the African aurochs, B. p. mauretanicus, and also some European aurochs, B. p. primigenius (particularly those from the Pleistocene), we see the opposite, namely dorsoventrally compressed horns at the base. Thus, the horns of this zebu steer resemble the Indian aurochs in this respect, thus they can be considered "primitive". I would love to see the bony horn cores of this individual, to see if they have keels. A bony keel on the dorsal and ventral ridge of the horn core was a trait of Indian aurochs, particularly in early individuals [2], that later was lost in zebus again. Whether or not these keels were visible in the living animals is unknown, as no keratinous horn sheaths of this subspecies have been preserved. Therefore it would be interesting to see the bony horn cores of that steer. 

The zebu skull that is interesting can be seen here and here. What makes the skull interesting is that it can be seen that the forehead is slightly convex, which is a trait inherited from B. p. namadicus and the opposite of what is seen in the other aurochs subspecies and taurine cattle (a planar or slightly concave forehead). Also, the profile of the snout is completely straight, while European aurochs and taurine cattle have a slightly convex bulge at the base of the snout. The profile of the zebu skull, and that of many other zebus, thus resembles that of wild B. p. namadicus in these two respects: 

The skull of the Indian aurochs in profile view is at the bottom right; a cross section of the horn with the keels can be seen at fig. 6

Too bad that there is no complete skeleton of the Indian aurochs available. Plentiful of remains of B. p. namadicus have been found, but always only fragmentary specimen consisting of few elements and never a complete skeleton. My suggestion would be to create a composite skeleton in order to get a more complete picture of the morphology of this aurochs subspecies by taking well-preserved remains of individuals of the same sex and size and create a (more or less) complete skeleton. The same has been done for the neanderthal, from which no complete skeleton is known either.  

Literature 

[1] Orlando et al.: The first aurochs genome reveals the breeding history of British and European cattle. 2015. 

[2] Bökönyi: Zebus and Indian wild cattle. 1997.  

Bos primigenius trochoceros?

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. 

A Pleistocene aurochs skull from Germany with massive and wide-ranging horns - Bos primigenius trochoceros?

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. 

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. 

Genome editing for "breeding-back" the aurochs

Traditional “breeding-back” takes a long time until satisfying results are achieved, also because cattle are a comparably slow-reproducing species. Also, “breeding-back” cannot revive the aurochs for several reasons, it can merely produce an imitation of the wildtype. That is why many dream of using genome-editing in modern “breeding-back” projects. Genome editing using the CRISPR-Cas9 method enables to cut and modify the genome of an organism, and to insert or exchange alleles in the genome. The now-dead Uruz Project (which now only exists on Wikipedia) started with the claim that they want to use genome editing for “breeding-back” in order to speed up the process. It sounded great, but there are some obstacles. 

First of all, only a handful of genes responsible for the phenotypic characters of interest in cattle have been resolved. For example, we know that a brindle coat colour is caused by a dominant allele on the Agouti locus, that the polled condition is caused by a dominant allele on the Polled locus, and the three alleles on the Extension locus and aggression in cattle is probably influenced by the MAOA locus (go here). But we have no clue which alleles are responsible for horn size or curvature, the various colour dilutions we see in Podolian cattle and Chianina (which are used in “breeding-back”), the size of the hump, the sexual dichromatism and many other traits. And some traits, such as body size, proportions and other morphological traits (which make up the most important differences between cattle and aurochs) are likely controlled by hundreds of genes or even more (cattle have 22.000 genes). Therefore, a lot of research would have to be done in order to use genome editing efficiently for “breeding-back” an imitation of the aurochs. 

Genetic linkage is kind of an argument pro and contra genome editing in “breeding-back” at the same time. It is possible that some morphological/optical aurochs-like traits are linked to wildtype traits with other functions (for example immunological, developmental, physiological). If the wildtype allele(s) for a certain morphological trait is inserted into another genome with genome editing instead of being introduced with traditional breeding, the wildtype allele for non-visible characteristics would not be transferred to the new genome. This is a scenario where genome editing would not be beneficial for the goal (to have as much wildtype alleles as possible) and where traditional breeding would be more effective. However, the opposite scenario would be equally as likely, that some wildtype alleles are genetically linked with domestic alleles on the same chromosome. If the wildtype allele and the domestic allele lie close together on the chromosome, it is not only impossible to get rid of the domestic allele without also losing the wildtype allele but it is also very unlikely that the linkage is ended by recombination. In this case, genome editing would be beneficial: the domestic allele could be cut out and replaced with a wildtype allele from the same locus from another cattle breed that still has the wildtype allele. This is the scenario where genome editing would be highly beneficial for “breeding-back”, and I believe this is what the Uruz Project was referring to when they said they want to use this technique. However, as outlined above, as long as the alleles responsible for the phenotypic traits of relevance, it is not possible to use genome editing for “breeding-back” effectively. 

This is where the fully resolved aurochs genome that was resolved in 2015 from a British Neolithic aurochs bull comes into play. So far, no particular gene has been identified that played a considerable role in the domestication of the aurochs. In horses, two such genes have been identified: one influencing the ability of the animals to bear weight on their back, and one influencing fear response and docility (here). If the same work was done for the aurochs, one could take these genes in the genome of modern cattle (preferably cattle that are already aurochs-like, not Holstein-Frisian) and replace their domestic alleles on these important loci and replace them with alleles taken from the aurochs individual. It has also been found that zebus have some wildtype alleles that were replaced by domestic alleles in domestic cattle (here). These could also be replaced by aurochs alleles in an aurochs-like cattle individual. This modification of the genotype of an already aurochs-like taurine cattle individual would be a reintroduction of organismic wildtype traits that could be very beneficial for the cattle’s survival in nature under natural selection (be it immunological, developmental, physiological, genomic by the removal of deleterious domestic alleles, morphological or behavioural). 

I think it might be possible (though more effortful) to go one step further: replacing all the domestic allele of an aurochs-like taurine cattle individual with those of the aurochs. The result would basically be a recreated aurochs. It would not be a recreation of the original genetic diversity of the wildtype, but at least one individual. As an aurochs enthusiast, I would of course love this scenario. But if that is not possible for technical reasons, even the reintroduction of single wildtype alleles that are lost in modern cattle would already be a success. I really hope that someone one day is going to try it (what would require the “the aurochs can be bred back anyway” mentality to finally disappear). 

The Vig bull and its horns

The Vig bull is one of the two almost complete aurochs skeletons from Zealand, Denmark. It's from the early Holocene and shows several injuries to the bone caused by arrows. The skeleton is likely a male because of its size, robust postcranial skeleton and long skull shape. However, compared to other finds from males like the London skull, the eye sockets are not nearly as prominent and the overall build of the skull not very robust. 

The horns are not as strongly curved as those of many other aurochs bulls, and also the angle between horns and snout is larger than average (about 80°). On Wikimedia Commons there is a nice photo of the skeleton in frontal view (here). I could not resist to track the skull out with a pencil and do a life reconstruction of the head and horns: 

Perhaps I made the snout look too feminine for a bull, but the skull is very slender. There is no general rule how much keratine to add to the length and thickness to the horn cores because apparently there was much individual variation in the aurochs.