By Sean Mitchell
Found carcasses are fascination. Yes, I am that guy that stops on the roads to check out road kill; behaviour that has really honed my wildlife identification skills. I recommend it to everyone. Being able to identify a species from a carcass or even whole skeleton is not that difficult. But, and I suspect this is your experience as well, we frequently don’t encounter whole carcasses in our rambles, but rather bits of skeleton; disarticulated and scattered; weathered, broken, or chewed upon. This is where identification skills are challenged. All is not lost, we can often (not always, but frequently) correctly identify to species based on relatively small amount of material. This is where forensics meets wildlife biology.
Here I provide some general pointers to help you identify a found species from little evidence. These are only a teaser and focussed only on the skull of animals larger than a beaver; the tips and tricks to do this successfully from all body parts could fill a book (and may soon do so… a project I am working on). A caveat here: rather than littering this blog with photo after photo to demonstrate structures, I am afraid I must task you, gentle reader, to look up some of these features (for example moose nasal bones). For the interested reader I also have keys I have developed for my courses to identify skulls; if you would like such please email a request to NRTG.
Imagine you are wandering through the forest and you find a broken skull such as below. How to determine species?
Partial skull of unknown animal
First, look at the eye orbit (if it is part of the skull). A complete, unbroken, orbit indicates an ungulate while an incomplete rim a carnivore. There is one exception to this: pigs, though ungulates, have an incomplete rim. Note, on this worn skull above the complete orbit is broken due to wear but it is still complete. By incomplete orbit see the bobcat and fox skulls below.
Next look to the front rim of the orbit. How many holes (properly, lachrymal foraminifera) are there? Cervids (antlered animals) have two holes; bovids (horned animals) and pronghorn only one.
If the entire upper jaw is present are incisor teeth present in upper jaw? If yes, it is horse, if no it is one of the deer family. While you have it flipped upside down are canine teeth present, or even just the sockets for canines. If yes, and teeth are large, it is an elk; if yes and teeth are small, caribou; if no canines present it is moose or deer.
Returning to looking at the skull from the side, are the nasal bones short, not extending past the forward most cheek tooth: this is a moose. If nasal bones are long, extending past the forward most cheek tooth it is deer. To distinguish between deer, return again to the front of the orbit. For each deer there is a lachrymal pit; if it is more than 10 mm deep it is a mule deer, if less than 10 mm a whitetail.
Going through this process, the unknown partial skull pictured above has a complete orbit (an ungulate), two lachrymal foraminifera (a cervid). We lack the jaw and nasal bones so must infer from location (Vernon BC) what is most likely. It is outside known range of caribou, in an area where deer are abundant but elk and moose not. Further, it is small relative to what would be expected from a moose. From all of this we infer it more likely a deer than moose. Finally, the lachrymal pit is more than 10 mm deep. This is therefore from a mule deer. Furthermore, there are no antler pedicles (‘burrs’) indicating it is a doe. Not bad identification from little more than half a skull.
So, for an ungulate, if we only have the front half of the cranium we can get to species. With the back half we could even take it to sex by presence of antler pedicles or shape of horn cores. In more advanced work we could even approximately age the animal by tooth wear. Clearly we can recover a lot of information from a skull.
Flip over skull, and count cheekteeth — the premolars and molars behind the canines — on one side of the upper jaw. If less than four; this will be from the cat family (cougar, lynx, bobcat, or domestic cat). If the skull is <100 mm long it is likely a domestic cat, >150 mm a cougar. Between those size ranges we look for how close the two ends of the broken eye orbit approach each other. Close in bobcat, distant in lynx. This is a relative measure and generally compared with known skulls to confirm your identification. Further confirmation comes from the number of openings between the auditory bulla and occipital condyle: one for bobcat, two for lynx.
Skull of bobcat (Lynx rufus)
Bear skulls are known for their massiveness; even a partial bear skull is striking by its size and weight. Bult black bear or grizzly? All we need is that part of the skull containing the last molar, or even just the socket of that tooth. If the tooth is >30 mm long it is grizzly; <30 mm is black bear.
Dog skulls, even wolves, are surprisingly light compared to bear, their tooth row behind the canines is also noticeably curved. The toothrow of a bear is straight and linear. Dogs have an elongated snout and many more teeth cheek (six) than cats.
Skull of red fox (Vulpes vulpes)
To distinguish unambiguously among fox, coyote, and wolf typically requires the full skull, including lower jaw, and so outside of the scope of this blog.
There you have it. Some very basic approaches to help you identify skulls from only parts. There are, obviously, key parts to have (the eye orbit, the tooth rows), and the more skull the better. However, it is quite remarkable how, with practice, you will find it quire easy to identify skulls from just a little bit.
NRTG offers wildlife courses which include greater detail on identifying species, sex, and age from carcasses. These courses include: Wildlife Survey Field Methods, Wildlife Survey Field Methods: Ungulates, and Wildlife Survey Field Methods: Carnivores (under development).