A couple of days ago I took Raven over to the 100-acre woods for a walk. I didn’t want to be out too long, and I debated between doing the forest loop, or walking back into the fields and returning via the back end of our 30 acres (an old railway bed, now an ATV trail, runs along the back of the properties providing a convenient off-road connection). I finally decided on the latter, mostly because I hadn’t been back there in a while, more than because I thought I’d see anything interesting. And for most of the walk, this held true; I didn’t see much aside from a few small flocks of birds, and since I hadn’t brought my telephoto lens, by the time we were reaching the railbed I still hadn’t taken any photos.
Right at the edge of the property there there’s a clearing with some exposed rock and some interesting boulders. I thought I’d maybe go check them out, just on a whim. I crested the crown of the rock, and on the other side spotted something white. Suspecting a skull, I went down to investigate. I was correct, it was a skull, but the skull was accompanied by nearly a complete skeleton. How cool!
I took a few photos, but mostly left it undisturbed. I briefly toyed with bringing it all back and trying to assemble it like a jigsaw puzzle, but I had nothing to carry it in, and what would I do with an assembled skeleton, anyway? I’m not the sort to display something like that in my living room, or even in my study. It was quite small, the whole pile probably only about 15 inches (38 cm) across, and I just figured it was something common, like a raccoon. The skeleton’s proximity to the highway, just a couple hundred meters/yards away, made me suspect that the animal had been hit but not killed on the road, and staggered here where it collapsed and eventually died. Probably it was picked over by scavengers and decomposed by carrion beetles and other invertebrates, allowing the bones to remain mostly together. The only thing I didn’t see there was the lower jawbone. Somebody may have picked it up and taken it away.
This evening, as I was starting this post, I decided to key it out just to be sure about the identity. I’ve kept most of my textbooks and lab manuals from my university courses (at least, those courses that I found interesting), including A Manual of Mammalogy that has more information than you’d ever think you’d need to know about how to identify mammal families by their skulls, as well as other useful lab and field techniques. It would have helped me considerably to have the lower jaw in the photo, since part of keying out skulls is using their dentition formula (number of upper/lower incisors, canines, premolars and molars, which differ in pattern/formula by family), but I made do. I reached the end of the key with the result that the skull didn’t belong to a raccoon at all, or even an opossum, my other suspect, but in fact was a member of the Canidae – the dog family.
Well, that surprised me a bit. It would have to either be a Red Fox (Vulpes vulpes) or a domestic dog, as it’s much too small to be a coyote (or a wolf, which I wouldn’t expect around here anyway). This key to North Dakotan mammals suggests Red Fox skulls to be 12.5 to 15.5 cm (5-6 inches) in length; the skull would fit at the small end of that range. Though most dogs have a high, sloping forehead, some long-nosed breeds might not show this as distinctly. I’m not sure if there’s a feature visible on all domestic dog skulls that can be used to tell them apart from wild canids, but I suspect there probably isn’t, so it’s likely impossible to rule out a small dog. However, since dogs are generally (though not always) kept in their owners’ yards, a fox is probably more likely to become roadkill.
I may go back and collect the skeleton after all. I’m still not sure what I’d do with it, but a Red Fox is a pretty cool find, not something you stumble across every day. It would also allow me to confirm (or correct) this ID, since I keyed it out just using the photos I’d taken, which obscured some features. It’s interesting to examine skeletons; since they’re on the insides of our bodies, they’re not something you get to see often.
For instance, I hadn’t noticed that the vertebrae have two lateral holes to the central main one (this may, perhaps, have been something learned in mammalogy class but since forgotten). The latter is, of course, where the main spinal cord runs, but the smaller holes allow passage of a main artery and vein and some smaller nerve bundles. The projections of bone to either side provide points of attachment for various muscles.
In the second photo, of the skull, you can see a long, thin arch running along the cheek. This is basically the fox’s cheekbone. In the front, it forms, in part, a portion of the eye socket (the remainder would have been cartilage that would have decomposed). In the back half, the lower jaw bone slots up inside, and the giant masseter muscle, which clamps the jaw shut, runs through the inside of the arch and attaches to a spot higher up on the skull. It’s this long length of the jaw muscle that gives it so much power.
Your own muscles do something similar. Put your fingers on your cheeks and clench your jaw a couple of times. You can feel the muscles contracting. Now move your fingers to your cheekbones. Nothing, right? Finally, put your fingers on your temple and clench your jaw again. There’s the muscle again. Neat, huh?