Halloween brought skulls and bones to mind. People brought in bones to our nature centers to share their finds, to offer donations, and for help with identification. We are most frequently asked about raccoon skulls, followed by fox. These may not be the two most common animals in Arlington, but smaller critters’ skulls are less easily found, more fragile, and don’t have exciting big teeth. Our largest wild animal skull, a deer skull, most people can identify on their own.
The easiest way to differentiate raccoon and fox skulls is to compare them to other known specimens, but if you don’t happen to have a skull collection of your own at home, here are a few tips. First, raccoons are bigger than you think – or maybe the truth is that foxes are smaller than you think. Both species typically range in weight from 6 to 15 pounds. For comparison, an average house cat weighs about 10 pounds. Raccoons can reach 20 pounds though, so don’t assume a larger skull is a fox!
The easiest way to distinguish skulls of these two species is to look for ridges on the top of the braincase. Fox skulls have two ridges that begin over the eye sockets and join a few inches back. We have two fox species in Arlington – the red fox, Vulpes vulpes and the far less common gray fox, Urocyon cinereoargenteus. Conveniently enough for skull ID mnemonics, the ridges of Vulpes join in a V, and the ridges of the gray fox, Urycon, join in a U shape. Raccoon skulls are rounded and smooth on top. You may see sutures, bumps, and a faint central ridge but nothing like the two distinctive ridges on foxes. A few other things to look for: the noses of foxes are longer and narrower proportionally, their eye sockets are more defined, and ok, yes, they often are a little bigger.
After raccoon and fox skulls, I’d say next most common one we see is the opossum. We love this one because it’s unmistakable. Look for a prominent ridge-like a Mohawk running along the top of the skull. Like all naturalists, I am fundamentally incapable of mentioning opossums without also noting how many many teeth they have – 50 – more than any other mammal in North America.
Whatever bones you find, one thing I love to look for are marks from gnawing teeth – bones are nature’s calcium supplement for lots of smaller critters, from snails looking to build strong shells to growing young chipmunks. So enjoy them bones, them bones… and I hope you had a happy Halloween!