The Raccoon Family

It has not always been easy to determine where exactly raccoons fit within the larger mammalian family tree. In part, this is because it's difficult to pin down exactly what defines them and makes them distinctive from their closest relatives. We can get some idea of this by looking at the taxonomic history of the group.

The scientific classification of living organisms we use today has its origins in the 1758 edition of Systema Naturae, by Carl Linnaeus. Raccoons live only in the Americas, but even in 1758, Linnaeus was aware of the existence of raccoons, having heard about them from his friend Peter Kalm, who had observed them in what were then the colonies of Pennsylvania and New Jersey. Based on Kalm's description, Linnaeus named this new species Ursus lotor - the "washing bear". It was one of four species of "bear" that he identified in that work, only one of which we'd still consider to be such today.

In 1780, by which time a second species had been identified, German naturalist Gottleib Storr decided that raccoons were distinctive enough to be given their own genus, Procyon. The next step came in 1825, when the great English zoologist John Edward Gray created what we would now call the "raccoon family", the Procyonidae. He did this by grouping raccoons together with two other types of animal, one originally identified as a type of civet, and the other as a lemur. Which, since we now know Gray was right, and they really are both racoons, goes to show just how puzzling early naturalists found these animals.

However, while Gray gets the credit for naming the group, it's significant that he didn't award it the ranking of "family" at the time, but instead designated it as a smaller division within, following Linnaeus, the bear family.

It might seem odd today that anyone would think a raccoon is a type of bear, but Gray did have his reasons. Perhaps the first thing to understand is that he was writing over thirty years before the publication of On the Origin of Species, and so wasn't talking about evolution, just a helpful means of classifying animals by their points of similarity. Indeed, he defined only two families of land-dwelling carnivorous mammal and the primary means he used for distinguishing them was the shape of their feet.

One group he identified as those carnivores that walk only on their toes, with the ankle and heel held well clear of the ground. Which meant that, under his scheme, the dog "tribe" was a division of the cat family. Raccoons, however, walk on the soles of their feet, just as humans do, in what's technically called plantigrady. So, taken together with the fact that he didn't think their nose was very cat-like, the raccoons went where Linnaeus had put them, with the bears. As did, perhaps less surprisingly, the wolverines and badgers.

By the 20th century, raccoons were generally recognised as a family in their own right and, when genetic analysis came along in the 1990s, there were no big surprises. By this time, it seems, the initial confusion had long since passed, and the definition of the family hasn't really changed since. We also know that, while they are admittedly more closely related to bears than to cats, their closest relatives are, in fact, the mustelids - the group including weasels, badgers, and otters, among others.

Even today, it's hard to come up with many obvious generalisations that are true of all members of the group. They are moderately-sized mammals, with many of the features, such as claws and sharp teeth, that unite them with the other carnivores. They all have flexible fingers, which originally evolved for climbing trees, and, indeed, all living members of the raccoon family can climb - albeit some are better than others. They also tend to have striped tails and facial markings but this is not universal and it isn't really clear what the evolutionary advantage of it is.

Compared with those of weasels, the teeth of raccoons are relatively unspecialised. They have the full set of three incisors on each side of each jaw that is seen in most mammalian carnivores; these are typically small, especially in the lower jaw. Behind these come the canine teeth, which are enlarged, but can be either a stabbing or a slicing blade, depending on the species. Procyonids typically have four sets of premolars, but the first is small, and sometimes missing altogether. The flesh-shearing carnassial teeth that are distinctive of carnivorans in general are present, but in some species have a reduced blade, making them less effective for their apparent purpose. Similarly, the molars, of which there are always two sets, are better adapted to crushing plant matter than to tearing meat.

These adaptations are due to the fact that raccoons in general are amongst the least carnivorous of all carnivorans, exceeded only by the pandas. While there is significant variation between species, for the most part, they are omnivores, eating a wide mix of both plant and animal matter. Indeed, it may be hard to think of any non-human mammal that is more omnivorous than the common raccoon.

In other respects, they are also not especially distinctive. They are not particularly noisy, but when they do make sounds they are the usual hisses, growls, and squeaks that you would probably expect. Their hearing and vision do not seem exceptional and, while they do have an excellent sense of smell and can communicate using scent marking, that's hardly unusual. Most are solitary, but some are not. They give birth to litters of young, which are initially blind and helpless, like those of many other carnivores.

When preparing for this annual series of posts, I often ask non-specialists how many different species belonging to the family in question they can name, to see which ones are the most widely known to the  (British) public. There seemed little point this time, but I did it anyway and got the answer I expected - one. This might be different in the Americas, since that is where all the species are found; even then, there are only three native to the US and only one of those (the obvious one) is actually called a "raccoon".

Which is one part of the problem: although I've been using the word "raccoon" here to refer to procyonids in general, most of them aren't literally raccoons and in at least some cases it's not at all obvious on casual inspection that the animal is even related. The exact number of species that should be included in the family has also been a matter of some debate. Normally, one finds that, in recent years, genetic evidence has shown us that many animals include more species than we previously thought, because some supposed subspecies or whatever turns out to be surprisingly distinct. But, while this has happened with the raccoon family, the overall trend has, if anything, tended to be in the opposite direction.

This is partly due to the four species of raccoon thought to be unique to various islands in the Caribbean, the product of millions of years of isolation from their mainland kin. Three of these were considered endangered, due to the small area of the islands concerned and increasing human development on them. More significantly, the fourth one, the Barbados raccoon (Procyon gloveralleni) first identified as a distinct species in 1930, had gone extinct less than four decades later, in 1964.

Only it hadn't.

Well, it died out, certainly. It's just that it never really existed. Studies in 2003 and 2008 confirmed that the Barbados raccoons, along with the still-surviving but endangered forms native to the Lesser Antilles and the Bahamas, were just regular, everyday, continental raccoons. In fact, they had probably only been on the islands for a century or two, having apparently been brought there by humans (although quite why is unclear).

So the "extinction" of the Barbados raccoon not only wasn't a sad day for global species diversity, it was actually a good thing - the elimination of an invasive pest that had been messing up the native ecology of the island. Granted, we'd done it without trying, but sometimes you have to take your victories where you find them.

Similar trimming has occurred in some of the other procyonid genera, too, so that we recognise fewer species in the family now than we did thirty years ago. Having said which, while it probably contains more species than most people realise, the raccoon family has never been an extensive one in the way that, say, the cats and dogs are. This year, I'm going to look at every currently recognised species in the group... and it isn't going to take the whole year to do it.

[Photo by "Isiwal", from Wikimedia Commons.]