From Chihuahua to Saint Bernard, which pass through the sights of Borzoi with their unusually tall skulls, dogs now appear in a remarkable variety of shapes, while all coming from the same ancestor, the gray wolf. This high innovation is recent, as it is linked to the intensive selections made over the past 200 years for the production of the 355 species now recognized by the International Cynological Federation.
But what do we know about the appearance of the first dogs, in prehistoric times? This is the question we answered in our article published on May 18 in the scientific journal Proceedings of the Royal Society B.
The same ancestor
All dogs are from the same ancestor: the gray wolf. At least 15,000 years ago, during the Upper Palaeolithic period (the exact date and location of the habitat is still being debated), fearless and aggressive wolves belonging to a now extinct species would have been attracted to settlers- human food, likely to take advantage of leftover food. .
Prehistoric people then approached these wolves, it brought them help to hunt or to defend their camps against the attacks of other predators. We would have tamed the less wild of them, breeding them and thus nourishing them over time.
This lifestyle is accompanied by many genetic, physiological, behavioral and even physical changes, most of which are unintentional. Among the morphological changes, archaeozoologists (experts in human-animal relations in the past) and paleogeneticists noticed differences in coat color, a decrease in size, less marked differences. between males and females and the preservation of younger traits – which translates into changes in skeletal dimensions with a strongly marked and shortened muzzle and tooth anomalies (loss or rotation in some teeth) more often due to lack of space.
In addition, a study conducted since the 1960s in Siberia showed that by selecting the most rare and least aggressive wolves of the generations (thus recreating the hypothetical conditions of the first encounters between men and wolves), the animals became more and more obedient, their level. of stress (valued by secretion of cortisol) decreased, and that they presented the same morphological differences as those observed by archaeozoologists during the transition from wolves to dogs. Domestication also changes the anatomy of the facial muscles, to allow for the raising of the eyebrows.
A diversification of dogs from the Neolithic?
Later in the Neolithic period, in Western Eurasia, people gradually chose a sedentary life and returned to agriculture. These changes in our way of life are likely to affect our dog sidekicks, making them even more different from their wild ancestors. In particular, prehistoric men were able to select morphologies that were adapted to perform certain tasks, such as hunting large games or defending camps and villages.
However, only a few studies have attempted to describe the morphology of dogs from the remaining bone. For example, a Scottish study attempted to change the face from the skull of a dog dated about 4,500 years ago and found in a necropolis in the Cuween Hill region of Scotland’s Orkney archipelago. In reconstructed bones, whose size evokes our modern border collie, silicone and clay are used to rebuild a number of muscles. A skin was then added, the fur was chosen to commemorate the gray wolf of Europe. A similar reconstruction was done recently for an older dog, dated about 7,600 years ago.
In addition, the method used is usually very inefficient and does not make it possible to accurately describe the shape of the bones (preferably we have estimates of the strength or length of the fissures from the measurements. made of tall bones, and of size indications from measurements made of skeletal elements). Thus, to date, there are no studies that have accurately and reliably documented the morphological variability of dogs on a prehistoric and European scale.
In our study, we took a sample of more than 500 lower jaws (mandibles) of European dogs dated from 11,100 to 5,000 years before our days, i.e. from the Mesolithic to the beginning of the Bronze Age, when dogs are well distinguished from wolves. We base ourselves on the mandible because it is the most frequent and best preserved bone in an archaeological context.
In addition, the mandible remains a good indicator of the overall shape of the head and it can be used to provide a practical definition of the differences in the shapes observed. We can therefore estimate whether the masticatory muscles are more or less developed, and which are most active during biting.
We used 3D techniques to accurately describe the shape of these mandibles, i.e. the size and proportion within the bone. To quantify this innovation and compare it to our dogs today, we used a repository consisting of about a hundred modern dogs of different breeds or returned to the wild state (Australian dingoes ), as well as some wolves (modern and ancient).
The result of our study
Our study showed, for the first time, that at this very early age dogs already have a variety of head sizes and shapes. Prehistoric European dogs had mandibles that were the same size as some today’s medium-sized dogs such as the husky or golden retriever, or the same size as our beagles today, or even small dogs such as the Pomeranian (also called the dwarf spitz) or the dachshund.
In any case, they all have smaller jaws than the smallest modern or archaeological wolves in our sample. We didn’t find very large sizes (like the modern Rottweiler or Borzoi Greyhound, for example) or very small sizes (like Yorkies or Chihuahuas).
In terms of form, we don’t recognize a serious form, so there is no equivalent to modified breeds like the Rottweiler, the Borzoi, the French Bulldog, the Dachshund or the Chihuahua. Most dogs have a typical shape, similar to today’s beagles or other breeds such as the husky, but there are some variations with longer heads (mandibles similar to Sloughi’s or whippet sighthound, or Pomerania).
If we expected this result and this lower variability in prehistoric dogs compared to modern dogs, we did not expect what we next showed.
We emphasize that part of the innovation of prehistoric dogs seems to have no equivalent in our dogs today or among wolves. Surprisingly, because we made sure to include all possible morphological types by integrating the excesses (small or large dogs with short or long muzzles, dogs with slightly altered cranial morphology such as beagles or dingoes). One might expect that prehistoric dogs would place themselves in a place of this diversity.
It is true that our modern sample was not complete at the time of the study, but since then we have done more analysis by adding stray dogs (with no particular selected morphology), and it would appear that they not enough. forms found in European prehistoric dogs. More than likely by adding dogs to the modern corpus, we have always made this observation. This leads us to wonder if certain forms will not disappear.
In addition, we know the anatomical peculiarities of prehistoric dogs compared to modern dogs, making it possible to identify them with certainty. These discriminatory behaviors can, among other things, illustrate dogs ’adaptation to choosing pressures related to their environment and their way of life. In fact, prehistoric European dogs had strong, arched jaws, suggesting that they used their temporal muscles more.
One possible explanation is that they ate harder, harder to chew foods than our kibble-fed dogs. Another assumption is that it would have been useful for them to protect camps and villages or to help catch large game when hunting.
Finally, we show greater flexibility within the mandible in archaeological dogs: in modern dogs, the shape of the front of the jaw is strongly associated with the back of the jaw, due to developmental constraints, while it is less common in the prehistoric. dogs. This greater flexibility could have made it easier for dogs to adapt to sudden dietary changes, for example.
In this study, we aimed to describe worldwide the morphological variability of European dogs in prehistory, by comparing them with modern dogs, without attempting to explain this variability or to follow the morphological evolution of dogs over time. in prehistory. . Future work is needed to understand, with precision, how geographical and cultural differences (affecting the place given to dogs in societies or their diet) may affect the morphology of our smoke allies. at this time.
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