From the Chihuahua to Saint Bernard, who passes the Borzois greyhounds with their incredibly elongated skulls, today’s dogs present a unique variety of forms, all descending from the same ancestor, the gray wolf. This high variability is only recent, as it is linked to the intensive selections carried out over the last 200 years to create the 355 breeds now recognized by the Fédération Cynologique Internationale. But what do we know about the appearance of the first dogs in prehistoric times? This is the issue we addressed in our article published today, May 18, in the scientific journal Proceedings of the Royal Society B.
Our research has for the first time shown that dogs already in this very early period had a wide range of head sizes and shapes.
All current dogs come from the same ancestor
All dogs come from the same ancestor: the gray wolf. At least 15,000 years ago in the Upper Paleolithic (the exact date and location of domestication remains a matter of debate), fearless and aggressive wolves belonging to a now extinct lineage would have been attracted to human camps, probably to take advantage of leftovers. The prehistoric men would then have approached these wolves, and they had given them help to hunt or protect their camps from attacks by other predators. We would have tamed the less wild ones of them, made them multiply and thus tame them over time.
This domestication has been accompanied by numerous genetic, physiological, behavioral, and even physical changes, most of them unintentional. Among the morphological changes, archaeozoologists (former experts in human-animal relations) and paleogeneticists have noticed variations in fur color, a reduction in size, less marked differences between males and females, and the preservation of fairly young features, resulting in changes in skull dimensions with a strongly marked and shortened muzzle and more frequent tooth abnormalities (absence or rotation of certain teeth) due to lack of space.
Moreover, a study conducted since the 1960s in Siberia has shown that by selecting the most curious and least aggressive foxes through the generations (thereby recreating the hypothetical conditions of the first encounters between men and wolves), the animals became more and more docile, their the level of stress (appreciated by the secretion of cortisol) decreasing and that they showed the same morphological differences as those archaeologists observed during the transition from wolves to dogs. Domestication would also have altered the anatomy of the facial muscles to allow the eyebrows to swell.
A diversification of dogs from the Neolithic?
Later, during the Neolithic in Western Eurasia, people gradually chose a sedentary and agricultural life. These changes in our lifestyle most likely affected our canine sidekicks, making them even more different from their wild ancestor. In particular, prehistoric men were able to choose morphologies adapted to the performance of certain tasks, such as hunting large game or defending camps and villages.
However, only a few studies have attempted to describe the morphology of dogs based on bone remains. For example, a Scottish study attempted a facial reconstruction from the skull of a dog dated to about 4,500 years ago and found in a necropolis in the Cuween Hill region of Scotland’s Orkney archipelago. On the reconstructed bones, the size of which evokes our modern border collie, silicone and clay were used to reconstruct the volume of the muscles. Then a skin was added and the fur was chosen to recall the European gray wolf. A similar reconstruction was made recently for an even older dog, dated to about 7,600 years ago.
Other studies, unfortunately scattered, have relied on measurements made on the bones to describe the shape of these prehistoric dogs. This research encounters the problem of preservation of bone remains (skull remains are rare and often very fragmented), refers to small samples and is limited to the study of specific regions or periods, without seeking to get more out of the variability of dogs in Europe on prehistoric scale. . In addition, the method used is generally very rudimentary and does not make it possible to accurately describe the shape of the bones (at best we have estimates of robustness or shoulder height from measurements made on the long bones, and size indications from measurements made on the skull elements). To date, no study has thus accurately and reliably documented the morphological variability of dogs on the prehistory and European scale.
In our study, we examined a sample of more than 500 lower jaws (lower jaws) of European dogs dated from 11,100 to 5,000 years before our days, i.e. from the Mesolithic to the early Bronze Age, when dogs were already well differentiated from wolves. We started from the lower jaw because it is the most frequent and best-preserved bone in an archaeological context. In addition, the lower jaw remains a good indicator of the general shape of the head, and it can be used to give a functional meaning to the observed variations of shapes. We can therefore assess whether the chewing muscles were more or less developed and which worked most during the bite.
We used 3D methods to accurately describe the shape of these mandibles, i.e. the size and proportions of the bone. To quantify this variability and compare it with our current dogs, we used a depot consisting of about a hundred modern dogs of different breeds or returned to the wild state (Australian dingoes), as well as a few wolves (modern and old).
The results of our study
Our study has for the first time shown that dogs already in this very early period had a wide range of head sizes and shapes. European prehistoric dogs had either lower jaws the same size as some current medium-sized dogs like husky or golden retriever, or the same size as our current beagles, or even small dogs like Pomerania (also called dwarf spear) or dachshund. In any case, they all had significantly smaller jaws than the smallest modern or archaeological wolves in our sample. We did not find extremely large (like modern Rottweilers or Borzois Greyhounds for example) or extremely small (like Yorkies or Chihuahuas) sizes.
In terms of form, we have also not identified a very extreme form, so no equivalent to heavily modified breeds such as Rottweiler, Borzoi Greyhound, French Bulldog, Dachshund or Chihuahua. Most of the dogs had an average physique, similar to today’s beagles or other breeds such as husky, but there was some variation with more elongated heads (mandibles similar to those of Sloughi or whippet sigthounds or Pomerania).
If we expected this result and this lower variability of prehistoric dogs compared to modern dogs, we did not expect what we demonstrated next time. We highlighted that part of the variety of prehistoric dogs did not appear to have an equivalent among our current dogs or among wolves. Which is surprising as we made sure to include all sorts of morphology by integrating the extremes (small or large dogs with short or long muzzles, dogs with a slightly modified cranial morphology such as beagles or dingoes). One might therefore have expected that prehistoric dogs would place themselves somewhere in this variation.
It is true that our modern sample was not exhaustive at the time of the study, but we have since performed further analyzes by adding stray dogs (without specially selected morphology), and it turns out that they are not enough to explain these unique forms observed in European prehistoric dogs. It is more than likely that we always make this observation by adding dogs to the modern corpus. This makes us wonder if certain forms may not have disappeared.
In addition, we have identified anatomical peculiarities in prehistoric dogs compared to modern dogs, making it possible to recognize them with certainty. These discriminatory characteristics may, among other things, illustrate dogs’ adaptation to selection pressures related to their environment and their way of life. In fact, prehistoric European dogs have strong, curved jaws, suggesting that they used their temporal muscles more. One possible explanation is that they ate harder, harder to chew food than our feed-fed dogs. Another hypothesis is that it would have been useful for them to defend camps and villages or help catch large game while hunting.
Finally, we showed greater flexibility within the lower jaw in archaeological dogs: In modern dogs, the shape of the front of the jaw is strongly associated with the shape of the back of the jaw due to developmental limitations, whereas this is less the case in prehistoric times. dogs. This greater flexibility could have allowed dogs to adapt more easily to sudden changes in diet, for example.
In this study, we aimed very globally to describe 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 development of dogs in prehistory. . Future work will be needed to strictly decode how geographical and cultural differences (which affect the space that the dog has been given in society or their diet) may have affected the morphology of our dog allies during this period.