Let us recapitulate the morphology and life appearance of the aurochs: it was large, had a short trunk and long legs, a long snout and horns facing forwards in a 60° angle relative to the snout. Right?
Yes and no. In fact, there might have been more variation on some aspects of the aurochs’ morphology than we usually expect. There is the danger of idealizing the aurochs’ life appearance by assuming that the typical or average morphology was universal.
Variation did not concern the aurochs’ body morphology and proportions. All aurochs specimen have a short trunk and long legs, resulting in a trunk length that equals the shoulder height in bulls and is a little bit shorter in cows, and all individuals, male and female, had a hump. But there was variation in the skull anatomy. Generally speaking, the skull of the aurochs had a longer snout than in most domestic cattle and a larger brain volume (go here for a post on the brain volume of the aurochs), which is not surprising, as a reduction in brain volume and a shortening of the skull are typical traits of domestic animals. However, the snout length apparently varied between the individual aurochs. While some skulls, such as that of the old Friemersdorf skeletal mount or that of the Sassenberg bull, have a really long snout, longer than in any domestic cattle heads I have seen so far, the Torsac dirac bull skeleton has a comparably short-snouted skull. The snout length of that specimen is actually similar to that of many domestic bulls. Male aurochs skulls usually also have very prominent eye sockets, more so than domestic cattle – but this was not the case in all male specimen. The Vig bull has a comparably slender skull, with less prominent eye sockets.
There also was considerable variation concerning the horns within the European subspecies. Wild yaks have very aurochs-like horns. They match those of the aurochs both in dimensions and curvature as well as colour. Go here. This horn shape and size displayed by wild yaks is the “standard” when we imagine the horns of the aurochs. However, there was more variation in terms of horn shape and size in the European aurochs compared to the current wild yak population. The basic curvature was always the same – the so-called primigenius spiral. But it was present in numerous variations. Some horns were quite wide-ranging with a comparably weak curvature (such as in the Vig bull), others had a strongly-expressed curvature (such as the Prejlerup bull). The 60° orientation relative to the snout is the arithmetic mean of what Cis van Vuure found to be the average horn orientation in European aurochs (50 to 70°). The variation, however, was larger. The Vig bull has horns in a 80° angle, a skull at the museum of Horsholm has a possibly even larger angle (the narrowest angle I have seen so far is that of the oldest aurochs skull with 40°, but that skull was found in Africa and therefore likely not of the primigenius subspecies). Since those skulls with more upright horns are from the Northern half of Europe, while those skulls with a sharper angle tend to be from Southern Europe, it could be that there was a north-south gradient regarding horn orientation. Horn length also varies not inconsiderably. The skull with the smallest horns I have seen so far is that of the Himmelev bull, while very large-horned specimen are f.e. the Sassenberg bull.
My latest aurochs reconstructions illustrate some the variation found in the European aurochs. The Torsac dirac bull has a snout comparable in length to many domestic bulls, the Kiew aurochs has comparably upright and weakly curved horns, similar to the Vig bull. The horns of some good Heck cattle, f.e. of the Wörth/Steinberg lineage, are not totally dissimilar to this horn shape.
Life reconstruction of the Torsac dirac bull (left, photo © by Claude Guintard) and the Kiev bull (right, photo © by Andrzej Zieleniak)
The variability of the European aurochs’ horns and also snout length suggests to me that this subspecies was genetically quite diverse. Time is not such a big factor here as most of the specimen I mentioned in the text are from the early Holocene.
What implications does this have for “breeding-back”? I think that “breeding-back” should be able to reflect the variability found in the European aurochs in its breeding results. Considering that some good Heck cattle, f.e. the bull Aretto from the Wörth/Steinberg lineage, have horns coming close to those of the Kiew or Horsholm specimen, and that some Taurus cattle, f.e. the bull Linnet, have horns resembling those of the Preljerup specimen, the variation spectrum for aurochs-like horn shapes is already present in the total “breeding-back” gene pool. Also the horn size spectrum of the aurochs, with some Wörth/Steinberg Heck cattle having horns matching the absolute and relative dimensions of very large-horned aurochs specimen. Now the challenge is to get rid of deviant (domestic) horn shapes and let natural selection do the rest (as the Oostvaardersplassen population shows, the primigenius spiral evolves after a certain amount of time in a variable population, go here for example). Breeding has yet to produce a snout length as long as in long-snouted aurochs specimen, which is not easy and as challenging as achieving the right trunk : leg length ratio.
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