How large were the largest aurochs?

The size of the European aurochs has been both over- and underestimated. The largest size estimate given in the literature I have seen so far was 230 cm at the withers (I don’t remember the source, unfortunately), the smallest for bulls was 145 cm. The latter is definitely inaccurate, as there is no evidence for European aurochs bulls with a withers height noticeably below 160 cm. But what was the upper size limit of aurochs bulls? 

 

The preserved skeletal material is the only reliable indicator for the size of the aurochs available as no living aurochs were measured. Complete skeletons are considerably rarer than finds consisting only of fragmentary material or single bone elements, but they are the better indicator for the size of the animal in life. But in order to give an accurate idea of the size of the living animal, it has to be mounted anatomically correct. Alas, most skeletal mounts of the aurochs have anatomical flaws. These flaws can make the withers height of the skeleton smaller or larger, depending on what is wrong. The Prejlerup bull skeleton, however, is mounted fairly correctly. I was unable to find a reliable source on the height of the skeleton. Using a photo of the skeleton in profile view with a person next to it whose height I know, I calculated the withers height of the skeleton and it turned out to be around 190cm. This is the largest size for a complete aurochs skeleton that I know of. However, it must be considered that the skeleton lacks the soft tissue surrounding the bones, so that the skeleton appears smaller than the individual was in life. For example, the intervertebral discs add quite a few centimetres to the length of the skeleton. The connective tissue between the leg bones adds to the height of the skeleton. The hooves alone might add 2 to 3 cm. And lastly, the skin and fat tissue adds one or two more centimetres. Therefore, it is not unlikely that the Prejlerup bull was 5 to 10 cm taller in life than its preserved skeleton. Thus, the bull might have been 195 to 200 cm tall at the withers in life. 

The Prejlerup bull is the largest complete skeleton from the European aurochs, but probably not the largest specimen found so far. Unfortunately, these specimens are not known from complete skeletons but from fragmentary, isolated remains. The perhaps largest European aurochs found is the London skull, exhibited at the British museum of London, which reportedly has a length of 91,2 cm [1]. This is very large, also compared to other aurochs specimens. The skull length in the other skulls observed by Nehring 1889 was between 64 and 72 cm [1]. Unfortunately, I do not have access to the original source by Nehring, so I don’t know if he specified what he means by “length” in his work – the length from the caudal end of the neurocranium to the cranial end of the nasal bone or to that of the premaxilla? I am cautious considering the huge size of the given length and assume it is from the end of the neurocranium to the premaxilla. This is still very large. 

How large was the animal that belonged to the London skull? In the lack of a complete skeleton, there is no other possibility to get an idea of the total body size than to extrapolate the size based on complete skeletons of other bulls. I used photos of four bull skeletons (Prejlerup, Vig, Sassenberg, Store-damme) in clear profile view and started to calculate. At first, I calculated the absolute skull length of the skulls of the skeletal mounts that I know the withers height of, the Sassenberg (165 cm), Prejlerup (possibly 190 cm) and Store-damme (175 cm) specimen in order to check if the calculation is plausible. The results were a skull length of 79 cm for the Prejlerup, 71,5 cm for the Sassenberg and 70,3 cm for the Store-damme skeleton. The latter two are in accordance with what was found by Nehring, the Prejlerup is slightly larger but the whole skeleton is larger than the other two. So the calculation results in plausible skull sizes for the given skeletons. The relation of the skull length to the withers height was 2,4 in the Prejlerup, 2,307 in the Sassenberg and 2,49 in the Store-damme and Vig specimen. Those are very similar values, the Sassenberg bull has the proportionally largest skull, but it has to be noted that it is partly a composite specimen. Under the assumption that the proportions of the London specimen were comparable to the other specimen, I calculated the possible withers height for the 91,2 cm long skull. The results were: 

If the proportions were identical to that of the Prejlerup bull: 218,4 cm

If the proportions were identical to that of the Sassenberg bull: 210 cm 

If the proportions were identical to that of the Store-damme and Vig bull: 226 cm 

If the proportions were intermediary between those of all four: 220,1 cm 

These are very large sizes. But we simply have that skull that was about 28% larger than what was found to be the average by Nehring 1889 – unless Nehring’s 91,2 cm for the London skull are inaccurate. However, I do not know Nehring’s sample size and if his sample was representative of aurochs from the northern half of Europe (which the other skeletons and most likely the London skulls were), and if all of the examined skulls were from males as females were smaller. There is at least one skull that might be comparable in size to the London skull, the Berlin skull. I saw this cranium two times, and I can firmly tell, it is huge. I don’t know if anyone measured that skull, however. But assuming the Berlin skull is of the same size or a similar size as the London skull, are the results of my calculation plausible? 

Well, there are several possible error sources. 

1. Nehring’s 91,2 cm for the London skull might be inaccurate 

2. The bull that belonged to the London cranium might have been oddly proportioned, i.e. with a head larger than usual for aurochs 

3. The photos I used might not reflect the natural proportions of the skeletons (I think they do) 

4. The measurements I took from the photos might be inaccurate or imprecise (in this case, the resulting absolute skull sizes for the skeletons would not be plausible, but they are) 

5. The four specimens do not reflect the variation in proportions within the European aurochs (since the values for the relative skull length are all very similar, except for the one specimen that is partly a composite, I do not think this is necessarily the case). 

The results of these calculations would certainly be more accurate if I had the possibility to take measurements from the actual bones, which I don’t have. But is a size between 210 and 226 cm for the largest aurochs plausible? Large wild yaks reach sizes up to 205 cm, gaur bulls 220 cm, and the extinct Bos (Bison) latifrons is said to have had a withers height of 230 cm. It must be considered, however, that these species have different proportions and longer spinal processes, resulting in a larger withers height. Thus, I am cautious. But I consider the 210 that result from calculating with the Sassenberg bull actually plausible for the largest aurochs. What would definitely be necessary is a) someone has to measure the London skull and Berlin skull to see if they really exceed 90 cm b) other suspiciously large aurochs bones, such as limb elements, pelves etc., should be checked – if they are by one fifth larger than the same elements from the complete skeletons, that is another hint that there were aurochs larger than 200 cm. However, extrapolating the size of an animal based on single skeletal elements is very risky in general. On the other hand, the London skull and the Berlin skull are noticeably larger than the skulls from complete skeletons which we know how tall they are. We need more complete material of very large aurochs to be sure how large they actually were.  

 

Literature 

 

[1] Frisch, W.: Der Auerochs – das europäische Rind. 2010. 

The coat colour variation in the Przewalski's horse #2

In the previous post, I wrote that wild-caught Przewalski’s horses from the 19^th and early 20^th century displayed more colours than the modern population does after the genetic bottleneck in the middle of the 20^th century. These colours included the lack of pangare, lightly coloured legs, possibly non-dun (at least a rather dark colour instead of the light sandy colour that many individuals show), and very lightly coloured individuals. 

In the comments, two photos were linked that, however, undoubtedly show modern Przewalski’s horses lacking pangare. They are from the population at the Hustai National Park in Mongolia and can be seen here (photo #1) and here (photo #2). 

This shows that the non-pangare allele is definitely still present in the population, albeit its frequency seems to be greatly reduced. What is also interesting is how dark the colour of the non-pangare individual on photo #2 is. It is not quite as dark as the stallion Schalun from the early 20^th century which I mentioned in the previous post, but it is certainly darker than a Gotland pony, which has been found to carry both the non-dun1 and the domestic non-dun2 allele, but not the dun allele. I think it is not unlikely that this individual has the non-dun1 allele – when you compare it with the stallion on photo #1, which is definitely bay dun, you can see a clear difference to the individual on photo #2. Looking at the other individuals on photo #2, it seems that they have the same base colour on the neck and face, and the rest is diluted by pangare, which is very prominent on these individuals. So they might have the non-dun1 allele too. If that is really the case, the non-dun1 allele might be present in more modern individuals than only those in this herd, just not as apparent because the colour is diluted by pangare and non-pangare individuals are pretty rare in the modern population. But without a genetic test on the Dun locus in these individuals this is a speculation. 

This sparked my interest in the Hustai herd and I searched for images on google. As it happens, I even found an individual with lightly coloured legs (go here). I also found a rather pale individual from Hustai NP, but it was in its winter coat and the winter coat is always lighter in colour. 

 

This shows two things: some of the colour variants considered extinct by the sources I cited in the previous post are still present in the modern Przewalski’s horse population, and the Hustai herd seems to be rather variable in colour. I am curious on the background of this herd – since the Przewalski’s horse was killed off from the wild in the 20^th century, this herd must descend from individuals in captivity, and I wonder which location(s) the animals are from as they preserve all these colour variants that have become incredibly rare in the modern population. 

The original coat colour variation in the Przewalski's horse

The modern Przewalski’s horse has a comparably uniform coat colour: a bay dun base colour often with a reddish tone, combined with the prominent countershading and white muzzle (pangare). This has become the standard colour scheme for wild horses. There is some variation, some individuals are more reddish than others, some are more lightly beige in colour, but apart from that, current Przewalski’s horses do not vary greatly in colour. 

However, what we see in modern Przewalski’s horses is the result of the genetic bottleneck due to the population crash in the 20^th century. Photos and descriptions of individuals prior to the genetic bottleneck event from the late 19^th century and early 20^th century show that originally there was much more variation in the coat colour of the Przewalski’s horse than what is the case now, also including colour alleles that have disappeared from the modern population. 

There were both very dark and also very lightly coloured individuals in the herds. They were not geographically separated but from the same populations and were often sold together [1]. An example for such a lightly coloured individual was a stallion caught from the wild and brought to the Haustiergarten Halle, Germany, in 1901 [1]. Some modern Przewalski’s can be more lightly coloured than others even today, but the photos show that some individuals prior to the bottleneck were very light in colour. A famous example for a dark individual is the stallion Waska, which was the first Przewalski’s horse brought to Europe and could be ridden [1] (you find a photo of him on Wikipedia). The photos of this and other dark individuals show that the countershading is slightly reduced, and that the colour is way darker and less shaded than in the modern Przewalski’s horses. I think it is well possible that these dark individuals had the non-dun1 phenotype caused by the d1 allele being present homozygotely on the Dun locus. This allele has been found in a 42.000 years old wild horse and a roughly 4.000 years old horse, both from Siberia [2]. The youngest date for the separation of the Przewalski’s horse’s lineage and that of the domestic horse was 38.000 years ago [3], making it possible that the non-dun1 allele was present in the wild populations before the lineages separated. Another stallion from the early 20^th century that was documented in photographs, named Schalun [1], was so dark that I think it is very unlikely that it had the dun dilution. It does not look as if it was the domestic non-dun2 mutation, the colour resembles much that of some Gotland ponies, which were found to have the d1 allele [2]. It is of course possible that Przewalski’s got the d1 allele via introgression from domestic horses but considering that the allele was already present in late Pleistocene wild horses, it is more parsimonious that the dark-coloured Przewalski’s horses were a reflection of the original wildtype diversity in the wild horse, if those individuals indeed had the d1 allele. 

Pangare (light ventral countershading with a white muzzle) is typical for wild equines, and all modern Przewalski’s horses have it. However, it was not uncommon that wild-caught Przewalski’s horses completely lacked pangare, f.e. many of the wild horses brought to Askania Nova in the early 20^th century [1]. These horses lacking pangare must have had the non-pangare allele Pa^np. It is certainly possible that this was the result of domestic horse introgression in the wild that undoubtedly took place, but I think it is also plausible that this allele first appeared in wild populations, as some cave paintings show horses that definitely lack pangare. Cave paintings, however, must be taken with caution. Only a genetic test of predomestic wild horse DNA samples could clarify if non-pangare was a wildtype or a domestic allele. 

There were also individuals with lightly coloured legs. Usually, in wildtype-coloured horses (be it bay, bay dun, black, black dun) the distal half of the legs is coloured dark to very dark, except for a light area at the back of the leg of varying extent. Apparently in some individuals this light area extended across the entire leg, resulting lightly coloured legs. There is at least one photograph of an individual having such legs [1], and descriptions of wild Przewalski’s from the late 19^th century mention lightly coloured legs. 

 

I did an illustration of the original coat colour diversity found in the Przewalski’s horse. It shows, from top to bottom and left to right, the colour type that is now prevailing in the population, the dark variant that is possibly non-dun1, the non-pangare one (I combined it with the dark variant, based on the stallion Schalun, but of course also lighter coloured ones could be non-pangare), the lightly coloured legs, and the very lightly coloured variant. All these illustrations are based on photographs of actual individuals that lived in the early 20^th century and often were caught from the wild. 

 

What happened to the colour variants not present in the modern gene pool anymore? One reason for their disappearance was the population crash in the 20^th century, which caused a reduction in allelic diversity. Another reason is, in fact, selective breeding. It was very likely the case that the lighter-coloured individuals with pangare and visible leg stripes were preferred in breeding because the responsible breeders thought that a wild horse must look that way [1,4]. This idealization of the Przewalski’s horse appearance caused these colour variants to disappear – there are no non-pangare individuals anymore (EDIT: There are in fact some non-pangare individuals surviving in Mongolian herds at least), and also no very dark, possibly non-dun, but also no very lightly coloured ones [1,4]. I do not think these variants were actively selected against, but apparently nobody paid attention on preserving them in the gene pool, resulting in their disappearance. 

 

The current Przewalski’s horse is not completely free of domestic horse introgression. As a consequence, domestic colour variants occur from time to time. Some herds may have individuals with a white stripe on the face [1], others show a chestnut colour [1,4], what means that the e mutation on the Extension locus has been introduced into the Przewalski’s horse gene pool by interbreeding with domestic horses. 

 

Therefore, while some wildtype colour variants have been lost in the last remaining wild horse, domestic ones have been introduced. This is of course not desirable for maintaining the original wildtype diversity. This could, theoretically, be fixed. For example, herds in which chestnut Przewalski’s have appeared could be tested for the eallele, and those selected out, what, on the other hand, bears the danger of selecting out wildtype diversity that is needed in the limited gene pool. The non-pangare allele could be reintroduced either by gene editing (which would be effortful) or crossing in a non-pangare domestic horse (which would be controversial for good reasons). But it is questionable if single colour alleles are really that important. 

EDIT: modern representatives of these colour variants can be seen here. 

 

Literature 

 

[1] Volf, Jiri: Das Urwildpferd. 1996. Neue Brehm-Bücherei. 

[2] Imsland et al.: Regulatory mutations in TBX3disrupt asymmetric hair pigmentation that underlies Dun camouflage colour in horses. 2015.

[3] Orlando et al.: Recalibrating Equus evolution using the genome sequence of an early Middle Pleistocene horse. 2013.

[4] Oelke, Hardy: Wildpferde gestern und heute – Wild horses then and now. 2012. 

Genetic research not done yet that would be helpful

Genetics are vital for understanding the evolution and domestication of horses and cattle. In recent years, genetic studies have helped to clarify where, when and how many times cattle and horses have been domesticated, which genes were involved, in the case of the horse and even resolved aspects of the phenotype of the extinct European wild horses. Genetics are also very important for breeding and thus for “breeding-back”. But a lot more research could be done to properly understand the aurochs, wild horse and their domestication. Often on my blog I am forced to engage in wild speculations because the genetic framework of the topic I am writing about has not been done yet. With this post, I want to give some impulses for genetic research not done yet that would be very useful for the topic of “breeding-back”, the aurochs and European wild horses.

 

- Resolving more coat colour loci and alleles in cattle. Many of the colour alleles in cattle are hypothetical, because the genetics of cattle colours are not as well-resolved as in dogs or horses for example. Thus, a rigorous study resolving many of the common cattle coat colour alleles would be fine, f.e. one that resolves the allele that is responsible for the recessive lack of red pigment in Podolian cattle, Tudanca, Grauvieh and Chianina, or the allele(s) that remove the rest of the pigments in the hair of Chianina. Resolving these recessive alleles and developing tests for those alleles would greatly help to remove them from “breeding-back” populations. 

- after that, testing the colour alleles in aurochs DNA samples. Studies have been done that resolved the colour genotypes of predomestic wild horses, which also revealed some surprises (f.e. that the leopard spotted complex was found in wild horses). It would be awesome if the same would be done with DNA samples from the aurochs. It could reveal surprises too. 

- Researching how many loci were affected in the domestication of the aurochs. That’s surely not an easy task, but it would be very interesting to know on how many loci aurochs and cattle differed, and if there are differences among cattle breeds. Some cattle breeds might differ from the aurochs on fewer loci than others.  

- Finding some key genes that had a role in the domestication of the aurochs and resolving the alleles. This has been done for horses in a recent study, it found two genes that probably had a key role in the domestication of the horse. The same could be done with cattle and aurochs. This would also be helpful for recreating the aurochs or at least creating an aurochs-like animal with the CRISPR-Cas9 method. 

- Studying the genetic background of the sexual dichromatism in Bos primigenius. It would be very interesting to know which loci and which genetic mechanisms are responsible for the sexual dichromatism seen in aurochs and cattle. Identifying individual alleles that are responsible for the well-marked dichromatism seen in the aurochs would also help to select for this trait in “breeding-back” cattle. 

- Resolving some genes involved in horn size and curvature. Currently, only two loci involved in the production of bovine horns are identified, the Polled locus and the Scurred locus. They only determine if the individual is polled or not and if the horns are scurred or not. But the genes involved in horn size and curvature are not studied. Horn size is likely a quantitative trait, but maybe there are one or a couple of loci that have a particularly large impact on horn size. Curvature is probably polygenic as well. If some loci involved in those two traits are resolved, the alleles found in the British aurochs of which the genome has been resolved in 2015 could be checked and traced down in living cattle, what would making selecting for aurochs-like horns much easier than it currently is. 

- Examining the Y chromosome of the Konik pony. So far, only the mitochondrial genome of the Konik pony has been examined. As domestic horses have a very limited Y chromosome diversity, finding unique haplotypes would be a strong hint for recent wild horse introgression, which would be the case if the Konik myth would be true. This, however, is very unlikely and it would be very nice to have it confirmed that also on the Y chromosome the Konik is a usual, robust domestic horse and not a surviving wild horse or a recent wild horse descendant.

- Resolving haplotypes in predomestic European wild horses and trying to trace them down in domestic horses. This would help to clarify how much wild horse introgression into the domestic horse gene pool there was in Europe, and also which breeds might have more influence from native European wild horses than others. 

- Testing European wild horses for the dun allele. So far, the dun locus was tested only for two Siberian wild or ancient horses, which is a way too small sample size to tell us about the frequency of the respective alleles. Also, the locus was not examined in European wild horses, so that we do not know with certainty if they were black or black dun.