How (not) to quantify aurochs-likeness in cattle

I have been trying to quantify aurochs-likeness in extant cattle multiple times and it turned out to be very difficult. It starts with the question of what is a “trait”. For example, is coat colour a trait or is it rather a complex of many traits (what types of melanin are expressed, where they are expressed et cetera)? Some traits also interfere with each other. As an example, leg length (i.e. proportions) influences height and other parameters. If a short-legged bull is only 150 cm tall, it is shorter in height than the European aurochs. If it had the right leg length it might be 20 cm taller, meeting the height of some European aurochs. Is, considering that, both the body size of the animal and the leg length deficient, or is only the leg length deficient? Even more problematic is the thought that not all traits are regulated by the same number of genes. Colour is regulated only by a handful of genes, perhaps roughly a dozen, while the bodily morphology is much more complex and influenced by many genes (I assume so because endocrinology influences the body morphology quite dramatically, and the hormone system is influenced by a very large number of genes). So which cattle individual is more aurochs-like, i.e. closer to the aurochs, one that has the right colour but a totally domestic morphology, or one that has the right morphology but deviant colours? If every defined “trait” (what is a trait?) is assigned an equal value, both individuals would be equally aurochs-like. This neglects the fact that in one individual a lot of genes are “right” and only a handful “wrong” while in the other a lot of genes are “wrong” and only a handful “right”. Therefore, the most objective and useful way to compare the phenotypic aurochs-likeness would be to compare every single gene that has an influence on the phenotype. This is practically near impossible as mammals have between 20.000 and 30.000 genes and we do not know the phenotypic impact of every single allele on every single gene. Therefore, an attempt to quantify even the solely phenotypic similarity to the aurochs necessarily has to be somewhat simplistic. I made lists of aurochs-like traits and scored a number of cattle breeds for those traits, each time a slightly different approach and the result always was that Sayaguesa and Lidia were among the two most aurochs-like breeds, “breeding-back” results were not included. It is very difficult to score “breeding-back” results as they are not as homogeneous as traditional breeds. For example, the horn size of Heck cattle varies greatly between individuals, herds and lineages. Averaging the traits found in the “breeding-back” results each would not account for the variability found within them. What can be done is scoring single individuals of “breeding-back” breeds/populations, but that leaves a lot of room for bias. One can take the best or the worst individual, or trying to figure out which individual might be representative of what is average for the breed, but that is very difficult and would, again, not account for the variability in the populations. 

All in all, I think trying to systematically objectively quantify the aurochs-likeness of cattle can only provide a very rough impression that is not any more useful than just looking at the cattle and comparing them. 

 

How bulky was the aurochs?

As mostly only bones are preserved of the aurochs, reconstructing the soft tissue surrounding them necessarily involves speculation. The anatomy of living wild bovines and cattle provide useful clues for that. But they do not tell us how pronounced the muscles really were, how large the intestinum was (this is relevant as domestic cattle have a much larger intestinum than wild bovines) and how much tissue surrounded the bones in general. 

Looking at a skeleton, there often is the tendency to underestimate the bulk of tissue that surrounded the bones. Those who are familiar with dinosaur paleoart will know of the term “shrink-wrapped” dinosaurs. That term arose when it was recognized that most dinosaur reconstructions from the 1990s and early 2000s were too skinny, often to a degree that makes anatomically no sense (which was a result of a countertrend to making dinosaurs extremely bulky in earlier 20^th century and 19^th century reconstructions). Nowadays dinosaur reconstructions much more appreciate the musculature those animals most likely had. I was not shrink-wrapping my dinosaurs in my drawings already back in the time before the term was even used in dinosaur paleoart. So, it is a bit ironic that I tend to make the same anatomical mistake in my aurochs reconstructions. 

The bones were surrounded by musculature, which has the greatest impact on the outer appearance of the animal. But the musculature was surrounded by fat tissue, which added a few millimeters to centimeters, by the skin, which added a few millimeters to centimeters, and by hair, which also added a few millimeters to centimeters. This necessarily involves a fair bit of guesswork to the reconstruction. I am always, without exception, unsure how much bulk I should add to the skeleton when doing a reconstruction. The actual shape of the animal would also not always be the same when fully grown, but it changed during the season (fatter during fall, skinnier during the end of the winter) and also across its lifetime as aging individuals get heavier, the bulls in particular. Comparing my recent reconstruction based on manipulating a photo of the Taurus bull Darth Vader III to my model of the Sassenberg bull (go here), I came to the conclusion that my model is probably not accurate. It is too skinny, particularly on the legs and the abdomen, making it a bit difficult to imagine this model as a living being. So I made some anatomical sketches trying to better appreciate the bulk of the soft tissue that surrounded the bones. 

 

The trunk 

The trunk is particularly difficult because even with seeing the ribcage and the curve of the spines in real, it cannot be derived from the skeleton how large the intestinum was. Domestic cattle have very large intestina, giving them the heavy appearance they have. Wild bovines, on the other hand, usually have a waist that narrows caudally (instead of being the centre of the mass). For my sketch, I tracked out a photo of the Store-damme skeleton that I had corrected anatomically using GIMP. The blue line shows what a young but fully grown aurochs might have looked like, similar to young fighting bulls and young wisents. The green line shows what an old bull might have looked like, based on the waist anatomy of old wisent bulls. The red line shows the domestic condition that is exhibited by most domestic cattle breeds. I have no precise anatomical method to come to these lines, I am looking at bovines in flesh and blood, guessing and drawing what I consider anatomically plausible. I am only quite confident that the red line is not plausible for an aurochs, since it is the domestic condition not found in any wild bovine. It also looks quite weird on a trunk as short as in the aurochs. 

 

The head 

 

The outer shape of the head also changes quite with age. Young bulls have a slender head while older bulls are bulkier. That’s why my 2019 model looked a bit juvenile (or actually subadult), its head was too slender. I wanted to do a model more credible for a grown bull this time, but it seems that I still “shrink-wrapped” it. Here are sketches that were done tracking out the London skull in frontal view: 

 

The left one is a “shrink-wrapped” version, the left one a version that I consider more plausible. Again I had no particular anatomical method to come to this sketch, but I tried to appreciate the facial muscles that undoubtedly were there and also the skin and fat tissue. 

The other sketches are based on the skull of the Sassenberg bull: 

 

The sketch on the right shows a “shrink-wrapped”, not anatomically plausible, version. It has a paper-thin skin, barely any facial muscles or salivary glands (that sit behind the lower jaw muscles), and there is barely place for the trachea and the oesophagus. The sketch in the centre is anatomically plausible to me, perhaps for a bull in its prime. The left sketch shows the maximum bulkiness that I still consider anatomically plausible. Old bulls might have looked like that. Looking at my most recent model (here) I think it is closest to the shrink-wrapped version, thus not anatomically plausible. So I added some bulk to the head and neck region with GIMP (and also painted an eye). The result looks much more plausible and life-like, I think: 

 

This shows that some aspects of the aurochs’ life appearance are very hard to strictly derive from the skeleton when trying to be very precise, and that trying to fabricate the “perfect aurochs model” is a continuous learning process. My next model is going to be better. I think I will reconstruct the Vig bull and Cambridge specimen (? cow) next time.