From Chihuahua to Saint Bernard, passing through the Borzoi with their incredibly elongated skulls, dogs of today present an exceptional variety of forms, while all descended from the same ancestor, the gray wolf. This high variance is only very recent, as it is related to the extensive selections that have been made over the past 200 years to create the 355 strains now recognized by the International Federation of Pathologists.
But what do we know about the appearance of the first dogs in prehistoric times? This is the question we addressed in our article published on May 18 in the scientific journal Proceedings of the Royal Society B.
All dogs come from the same ancestor: the gray wolf. At least 15,000 years ago, during the Upper Paleolithic (the exact date and location of domestication is still debated), brave and aggressive wolves belonging to a now-extinct lineage were drawn to human settlements, possibly to take advantage of food scraps.
Subsequently, prehistoric men approached these wolves, helping them to hunt or protecting their camps from the attacks of other predators. We would tame the least ferocious of them, make them breed and thus domesticate them over time.
This domestication has been accompanied by many genetic, physiological, behavioral and even physical modifications, most of which are unintentional. Among the morphological changes, archaeal zoologists (experts on human-animal relationships in the past) and paleontologists note differences in coat color, decrease in size, less pronounced differences between males and females, and preservation of traits rather than juveniles – which translates to changes In cranial dimensions with a pronounced and severely shortened muzzle and dental abnormalities (absence or rotation of some teeth) are more frequent due to lack of space.
Furthermore, a study conducted since the 1960s in Siberia showed that by selecting foxes that were more curious and less aggressive across generations (thereby recreating the hypothetical conditions for the first encounters between men and wolves), the animals became more resilient, their stress level decreased (estimated by cortisol secretion), And that they presented the same morphological differences as those observed by archaeal zoologists during the transition from wolves to dogs. Domestication would also have modified the anatomy of the facial muscles, so as to allow for eyebrows to be raised.
Diversity of dogs from the Neolithic period?
Later during the Neolithic period, in western Eurasia, humans gradually opted for a sedentary life and switched to agriculture. It is likely that these changes in our way of life affected our side dogs, making them more different from their wild ancestors. In particular, prehistoric men were able to choose forms adapted to performing certain tasks, such as hunting large game or defending camps and villages.
However, only a few studies have attempted to characterize canine morphology from bone remains. For example, a Scottish study attempted to reconstruct the face from a dog’s skull dating back around 4,500 years and found in a cemetery in Queen Hill in Scotland’s Orkney archipelago. On the reconstructed bones, whose volume evokes the modern frontier Collie, silicone and clay have been used to reconstruct muscle volume. Then leather was added, and the fur was chosen to remember the European gray wolf. A similar reconstruction was made recently of an older dog, dating back about 7,600 years.
In addition, the method used is generally very primitive and does not make it possible to accurately describe the shape of the bones (at best we have estimates of durability or height at the shoulders from measurements made on long bones, and volume indicators from measurements made on the elements of the skull). Thus, to date, no study has accurately and reliably documented the morphological variation of dogs on a prehistoric and European scale.
In our study, we sampled more than 500 lower jaws (mandibles) of European dogs dating back between 11,100 and 5,000 years before our days, from the Mesolithic to the beginning of the Bronze Age, when dogs were already well differentiated from wolves . We relied on the mandible because it is the most common and best preserved bone in the archaeological context.
Furthermore, the lower jaw remains a good indicator of the general shape of the head and can be used to give functional meaning to the shape changes observed. So we can estimate whether the masticatory muscles were more or less developed, and which ones were more influential during the bite.
We used 3D methods to accurately describe the shape of these mandibles, that is, the size and proportions within the bone. To estimate this variance and compare it with our current dogs, we used a reservoir consisting of about a hundred modern dogs of different breeds or brought back to the wild (Australian dingo), as well as a few wolves (both modern and ancient).
Our study results
Our study showed, for the first time, that in this very early period dogs already had a variety of head sizes and shapes. European prehistoric dogs either had jaws of the same size as some of the current medium-sized dogs such as the husky or golden retriever, or the same size as the current beagles, or even small dogs such as the Pomeranian (also called the dwarf spitz) or the dachshund.
In any case, they all had jaws much smaller than the smallest modern or archaeal wolves in our sample. We didn’t find very large sizes (like modern Rottweilers or Borzoi Greyhounds, for example) or very small sizes (like Yorkies or Chihuahuas).
Also in terms of shape, we have not defined an extreme form, so there is no equivalent to highly modified breeds such as the Rottweiler, Borzoi, French Bulldog, Dachshund or Chihuahua. Most dogs had a medium shape, similar to today’s beagles or other breeds such as the Husky, but there was some variation with more elongated heads (the lower jaws similar to those of Sloughi, whippet sighthounds, or Pomerania).
If we expected this result and this low variance of prehistoric dogs compared to modern dogs, then we did not expect what we showed next.
We have highlighted that part of the diversity of prehistoric dogs does not seem to have a parallel among our current dogs or among wolves. Which is surprising, given that we made sure to include all possible types of morphology by incorporating extremes (small or large dogs with short or long muzzles, dogs with slightly modified skull morphology such as the beagle or the dingo). So one might expect prehistoric dogs to place themselves somewhere in this contrast.
It is true that our recent sample was not comprehensive at the time of the study, but we have since performed additional analyzes by adding stray dogs (without specifically defined morphology), and it turned out to be insufficient. To explain these unique forms observed in European prehistoric dogs. It is likely that by adding dogs to the modern body, we are always making that observation. This leads us to wonder whether some forms may not go away.
In addition, we determined the anatomical characteristics of prehistoric dogs compared to modern dogs, which makes it possible to identify them with certainty. These discriminatory traits can, among other things, explain dogs’ adaptation to selection pressures related to their environment and way of life. In fact, European prehistoric dogs had a strong, arched jaw, indicating that they used their temporal muscles more.
One possible explanation is that they ate foods that were more difficult to chew than dogs that fed our food. Another hypothesis is that it was advantageous for them to defend camps and villages or to help catch large game when hunting.
Finally, we demonstrated greater flexibility within the mandibles of relic dogs: in modern dogs, the shape of the front of the jaw is closely related to the shape of the posterior part of the jaw, due to growth limitations, whereas this is not the case in prehistoric dogs. This greater flexibility would have made it easier for dogs to adapt to sudden changes in diet, for example.
In this study, we aimed to describe the morphological variation of European prehistoric dogs globally, by comparing them to modern dogs, without attempting to explain this variation or follow the morphological evolution of dogs during prehistoric times. Future work will be necessary to decode precisely, how geographic and cultural differences (affecting the place a dog is given in societies or their diet) might affect the morphology of our canine allies during this period.
This article has been republished from The Conversation under a Creative Commons license. Read the original article.