This post has been made possible by Peter Stockwell from the UK who addressed me to this specimen and provided me with interesting photos and information – many thanks for all the effort!
The Sedgwick Museum of Earth Sciences, Cambridge, UK, has several skulls or skull fragments on display labelled as aurochs. But one of them looks really atypical in having upright horns of a comparably weak curvature. The orientation of aurochs horns in relation to the skull usually varies from 70° to 50° according to Van Vuure 2005, some skulls might slightly brake the rule but it is apparent even from that broken frontal bone that the horns of this individuals seem to have an angle of beyond 90°, perhaps even 100°. Actually, these horns are barely like those of any other known aurochs crania but resemble those of many domestic cattle forms.
Some aurochs skulls, such as that of the Vig specimen, have horns that are more upright than the average. And the curvature varies from tight and narrow to more wide-ranging. But this skull definitely is a big leap from the end of the spectrum with no intermediate forms that I know of.
The photos are owned by Peter Stockwell.
The question is, then, if the skull fragment is that of an aurochs at all. The horns are, despite being atypical in orientation and curvature, still large and thick compared to the frontal bone carrying them. Unfortunately, much of the cranium is not preserved so we cannot check it for other diagnostic wild type traits, such as a large braincase, elongated skull (especially nasal bones), comparably small orbitals, straight to slightly convex profile and other features. The frontal bones, however, are obviously broad and well developed and the measurements I was provided with show that the specimen was in the size range of large domestic bulls at least (the distance between the horns on the specimen is 23cm, which is between those I find my two Taurus bull skulls; looking at the skulls and the individuals they are from I expect some variation on this metrical trait and I have no measurements from aurochs at hand) and therefore compatible with the aurochs (not all aurochs were giants, and the skull does not seem to be significantly smaller than the more typical skulls next to it on the photos). The horns are large also in absolute size. The distance between the complete tip and the broken tip is 83 cm, the circumference at the base 43 cm, which is well within the aurochs size range and well larger than in domestic cattle.
But equally as important as physical traits to find out the true nature of the skull fragment are location and age. I was told that the specimen was excavated at Barrington, Cambridgeshire, UK, in the year 1900. The exact age of the material was unfortunately not to be found out. But judging by its state, it is very plausible that it is older, or even way older, than mere two or three millennia, so it is definitely possible that the individual belonged to the predomestic British aurochs population. If the skull fragment is as old or younger than the arrival of domestic cattle on the British isles in the Neolithic, it is possible that the atypical horn shape of this individual is the result of interbreeding with domestic cattle. It has been supported by genetic data recently that local aurochs left a genetic trace in domestic cattle of Europe in several cases, but the reverse is possible as well – domestic genes may on occasion have left a trace in local wild populations, as it also happens between wolves and dogs or pigs and wild boar. It is likely that these domestic alleles are not that successful in the wild gene pool, but may produce variations visible in single animals, and this atypical aurochs skull might be one example if it is geologically possible. Precise dating and/or an aDNA test could resolve that question.
But let us assume this individual was a pure, predomestic aurochs. Should this deviant skull allow a broader range for what is permitted in breeding-back? I would say no: this skull is obviously a unique, atypical one, one of those very rare cases in a wild population. Furthermore, all existing breeding-back strains are rather variable concerning horn curvature and it is apparent from existing breeding projects that removing all those variants from the pool takes a rather long time. Allowing that kind of horns in a herd would make it even more difficult to establish the typical primigenius curvature, especially since we do not know the particular genes that play a role in the development of the shape of the horns. Besides that, undesired traits are going to reappear on occasion anyway, so this kind of upright, not tightly curved horns will be probably among them because of its common presence in domestic cattle.