Our curiosity is tireless, and after finding skulls in the field we usually wonder what species they might belong to. Task that must always be carried out respecting current legislation. Today we are going to create a practical scenario about the difference between a fox skull and a dog skull. We only know that it has been found in a pine forest in the Sierra de Guadarrama, without any further clues. So in the post we will show how to identify a fox skull and a dog skull, let’s get started!
Difference between herbivore and carnivore skull
The first thing we would have to rule out is that it belongs to a herbivore. In order to solve this question, it is always good to analyze the type of teeth in our skull. Carnivores are going to give themselves away quickly, not only do they have highly developed canines, but they also have molars adapted to cut meat (Tellería). The so-called butcher teeth are a delight of evolution, formed by the last upper premolar and the first lower molar, they will generate ‘natural scissors’ adapted to be able to feed effectively on meat.
First test passed, it is a carnivore. However, there are still many species to be ruled out. The canids, contrary to the rest of the families represented in the Community of Madrid, are going to be characterized by having a very elongated snout, which makes room for a versatile dentition, not as adapted for meat consumption as that of felids, for example (Wang, 2008). The three species of canids present in our region have the same number of teeth, a character that, although it does not allow us to distinguish them from each other, closes the circle more.
Identifying a herbivore skull
In one half of the upper jaw we find 3 incisors, 1 canine, 4 premolars and 2 molars. Changing the number of molars in the lower jaw from 2 to 3. Usually you will see all this information summarized in the so-called dental formula, which in this case would remain as: I 3/3, C 1/1, PM 4/4 , M 2/3 (Cabrera, 1914). We have a canine.
Size matters, a lot. The skull of a fox will be around 15 cm long (Gomes, 2016), and may overlap with various breeds of dogs, however, it allows us to remove the wolf from the equation with about 23-25 cm in length (Iglesias & Spain -Baez, 2017). To exemplify the differences, we have obtained public data on skulls associated with official institutions, which you can consult at “Skull-base” (Pereszlényi, s.f.). The infographic that accompanies this article (the previous image) compares to scale the skull of a fox (15.4 cm) with that of a boxer (20.5 cm).
Although the enormous morphological variation of dogs can sometimes complicate our existence; Under conditions of similar length, the dog’s skull is going to be considerably broader, stockier, and heavier. While the boxer’s skull weighs 337 grams, the fox barely reaches 76.6 grams (Pereszlényi, s.f.). The length of the muzzle also shows marked differences, with the fox once again standing out for the gracefulness of its long, thin snout. The canines of the dogs follow the same trend of the skull in general, they are shorter and broader at the base, in contrast to those of the fox, which are much finer and with such a length that the upper canines can protrude slightly from the lower jaw (Zumeta).
One of the most typical differences between dogs and foxes is going to be found in the side view. While dogs have a concave profile, foxes will have a much straighter muzzle-front transition (Zumeta).
However, there are many dogs with many facial angles in their dorsal profile, so we are going to use a wild card. The most subtle but most informative difference that we are going to discuss today, we see it highlighted with the number 1 in the top view of the skulls (cover image). We are marking the upper part of the orbit, the so-called zygomatic process of the frontal bone (O’Malley, 2007). The fox, unlike the dogs, will present some slight depressions that, together with the rest of the clues that we have described, allow us to reach the final solution. The skull in the previous image belongs to a dog.
differences between dogs and foxes in the side view
As you can see, with only one of these characteristics it is difficult to determine which species a skull belongs to, in fact, there are so many that the ones we have discussed in this post are just some of the few that we observe between both species.
Therefore, with this article we seek to inaugurate a new series of thematic posts within the Nature in the open section with which we will explore the morphological differences at the bone level between different species of the Madrid fauna. Don’t miss them! We would like to remind you that the possession of animal remains of any kind, without the corresponding license, is punishable by law.