Pleistocene (Pt 12): Dire Wolf Redux

I have previously discussed the dire wolves of Pleistocene North America, but really only in the context of how even earlier dogs were much scarier. Those earlier, bone-crushing, dogs were still around in the early Pleistocene, but they didn't survive the early Ice Ages, possibly because they were too specialised to cope as the climate changed. The dire wolf, on the other hand, first appeared at around this time, and survived long enough to live alongside humans.

The dire wolf (Canis dirus) was a very close relative of the grey wolf that we're all familiar with today. Grey wolves, despite their broad modern distribution, first evolved in Europe and Asia. Indeed, the sudden appearance of the Etruscan wolf (Canis etruscus), thought to be a direct ancestor of the living wolf, in the so-called "Wolf Event" shortly before the dawn of the Pleistocene, had a dramatic effect on European wildlife. Modern wolves, however, while widespread in the Old World, did not enter the Americas until surprisingly late, and did not travel south of the Canadian Arctic until the Ice Ages were almost over, around 0.1 million years ago.

Dire wolves, however, were there much earlier. So where did they come from? Although there was some suggestion back in the 1980s that they were actually South American in origin, the more modern consensus is that they were native to the northern continent. The most popular theory seems to be that dire wolves evolved from Armbruster's wolf (Canis armbrusteri). In fact, the latter continued to survive in its original form alongside its descendant until about 0.3 million years ago, although it does appear to have been steadily pushed eastward and southward during this time.

Another species of wolf living in North America at this time was Edward's wolf (Canis edwardii), which was probably closer to coyotes and jackals than to true wolves, and may have evolved from, or be related to, Johnston's coyote (Canis lepophagus), which had died out with the coming of the Ice Ages.

Armbruster's wolf was a fair-sized animal, and was itself likely descended from something that had crossed over from Asia. At some point, though, it evolved into an even larger form: the dire wolf. Quite when this happened seems to be a matter of some debate, and I've seen estimates ranging from 1.8 to 0.5 million years ago. This could well be due to the fact that there's a fairly gradual change from Armbruster's wolf to the dire wolf, with a number of intermediate fossils known. It may depend, then, on where, or even if, you choose to draw the line between them. I suspect, therefore, that figures of 1 million years ago or so are likely the most accurate.

At any rate, what was the dire wolf actually like? Being such a close relative of the living grey wolf, we can say that it likely had a lot in common, both in terms of physical appearance, and in habits. They were very widespread, being found, at some point or another, across almost the entire North American continent, from Canada to Mexico, with fossils also being known from Venezuela, Bolivia, and Peru. They seem to have lived in grassy plains, forested mountains, and everything in between, much as modern wolves do.

Famously, of course, the dire wolf was big, probably the largest ever member of its genus. On the other hand, it wasn't quite as large as you might think, and likely overlapped with modern grey wolves. That is, small dire wolves were probably about the size of timber wolves, the largest subspecies in modern North America. Indeed, they typically stood around 77cm (30 inches) at the shoulder, which is quite a bit shorter than most timber wolves.

On the other hand, they do seem to have been rather more muscular, and that's where the extra bulk comes from. It's hard to say, from a skeleton alone, just how much all that muscle and flesh weighed, but scientists have tried. We have, after all, literally thousands of dire wolf fossils from the La Brea tar pits, and we also have more than enough skeletons of living canid species that we can compare with actual body weights.

Since it's a fair bet that the bodily proportions of dire wolves were much like those of living wolves, once you take account of things like the thickness of the bones and so on, we ought to be able to make better guesses about the weight of dire wolves than, say, dinosaurs, which have no close living relatives. This sort of analysis gives us a best guess of around 68 kg (150 lbs) for the eastern subspecies of dire wolf, with western forms being about 10% lighter.

That's quite a lot, only slightly less than the weight of the largest timber wolf ever recorded. And, remember, it's an average, so, essentially, the biggest wolf you're ever likely to see today would be merely ordinary for a dire wolf - and a lot of them would have been bigger. For comparison, it's somewhere between the weight of a rottweiler and an English mastiff, and while the snout would have been longer, the overall build probably wasn't too far off from those breeds.

Given this, it comes as no great surprise that dire wolves ate fairly large prey. We can tell this not just from their overall size, but from details of their jaws. The shape of the skull suggests that they had especially large temporalis muscles, one of the main muscles used to generate bite force, and they also had unusually large carnassial teeth. In living animals, this is what we find in animals that take down large prey, and we can infer that the same was likely true of dire wolves. The shape of the jaw also supports this suggestion, with that dire wolf being about what you'd expect for something that attacks particularly large animals.

Specifics are rather less clear, although, if they were anything like living wolves, they probably ate just about anything they could chase. For that matter, they likely ate carrion, too, especially given the absence of hyenas or jackals in their ecosystem. Chemical analysis of dire wolf bones from La Brea suggests that, at least in that part of America, their favoured prey were the then-prevalent species of bison (Bison antiquus) and horse (Equus occidentalis), both of which are now extinct. They also seem to have eaten such animals as Harlan's ground sloths, mastodons, and North American camels, but to have generally avoided elk or moose. Given their range, there is, of course, no particular reason to assume that this was always true beyond California.

Given the huge number of fossils found at La Brea, dire wolves surely hunted in packs, as modern wolves do (and coyotes, for example, don't). We can even make some inferences about how those packs were structured. Among living canids, males are slightly larger than females, but the difference isn't too dramatic. This is because they don't need to compete much for access to mates, since wolves and the like tend to form stable pair-bonds rather than harems.

So far as we can tell, dire wolves were no different from living wolves in this regard, with females only slightly smaller than males. So, given all their other similarities, it's almost certain that they lived in packs very much like those of grey wolves today. That is, a single pair of mates, plus all their offspring of the last couple of years or so, with the occasional larger pack made up of two or three such family groups.

Dire wolves died out around 12,000 BC, along with most other large animals on the continent at the time. It's unlikely that humans hunted them to extinction directly, but they probably did hunt the food that they were eating, while leaving the smaller prey that grey wolves and coyotes relied on broadly intact.

[Painting by Charles R Knight, in the public domain]