Wolves at the Campfire

There's an internet meme, which exists in several different variants, that makes a half-serious joke about dog domestication. A typical version shows a picture of a wolf ostensibly heading to a camp of stone age hunters, hoping to get some food, and thinking "what's the worst that could happen?"... followed by a second picture captioned "thousands of years later" and showing an inbred domestic dog dressed in ridiculous knitwear. The second part is an accurate enough description of what thousands of years of domestication and directed breeding have done to at least some dog breeds. 

But what about the first part? That's showing what's probably a common understanding of how wolves originally became domesticated and turned into dogs. Essentially, dogs domesticated themselves, with those wolves that were least wary of humans, due to whatever quirk in their individual personalities, being the ones most likely to get close to them. Over time, there was further selection in this direction, with the friendliest wolves also becoming the most popular/useful to the humans until, eventually, domesticated breeding was able to take over. 

Miocene (Pt 17): A Diversity of Dogs

Eucyon

As North America dried out in the Late Miocene, and slowly transitioned towards the deserts and open grasslands that became dominant across the central parts of the continent, it wasn't just the herbivores that were forced to adapt. Carnivores may not have been affected so directly, but, if their food source was changing, they had to do so too.

There were two particularly significant changes among the North American mammalian carnivores that took place around this time. One was the extinction of the bear-dogs, a group with a long history on the continent that was, by this time, typified by relatively large animals that would have looked more like bears than dogs (although they were neither). Over in Europe and Asia, the bear-dogs survived for rather longer, although even there they struggled...  but in North America, the changes were too extreme for them to cope with, and they died out as the Late Miocene dawned.

Miocene (Pt 13): The Time of No Cats

Aelurodon

Today, there are a number of native cat species in America. The North has its bobcats, lynxes, and puma/cougar/mountain lions while, further south, there are even more species (ocelots and jaguars being merely the most obvious). At the dawn of the Miocene, 23 million years ago, however, it was a somewhat different story.

While there was nothing similar in the south, there had been plenty of cat-like animals on the northern continent before. True, they had not literally been cats, but rather nimravids, a group of remarkably cat-like animals that lived long before actual cats existed. The climatic changes of the Early Miocene seem not have suited them, however, and almost died out as the new epoch dawned. It's possible that one, Dinictis, a bobcat-sized sabretooth, did manage to struggle on for a few million years, but even that is debatable. But, otherwise, while their relatives, the barbourofelids, continued on in Europe, to eventually be replaced by actual cats, in North America... there was nothing.

Prehistoric Mammal Discoveries of 2018

Gordodon,
a new non-mammalian synapsid described this year

And so another year approaches its conclusion. As usual, I will wrap up here with a post looking at things from a slightly wider perspective. This time around, as I did last year, I am going to take a brief look at a range of scientific papers on fossil mammals that were published in 2018. There's not going to be any particular theme here beyond that, merely a list of things that caught my interest, and that were not, for various reasons, included in the blog proper. So, here we go:

Beginnings and Endings

In the modern day, it's pretty easy to tell mammals and reptiles apart. But, if we go far enough back in time, that eventually ceases to be so true. A common misunderstanding is that mammals evolved 'from' reptiles, but, in reality, mammals and reptiles are separate evolutionary lines that have lived alongside one another since long before there were dinosaurs. At least, that's true if we use the modern definition of 'reptile' since, of course, the animals that mammals really did evolve from would have looked an awful lot like reptiles if we'd been able to see them in the flesh.

Dire Wolves and Direr Dogs

Reconstruction of a dire wolf

[For more on dire wolves specifically, see: Dire Wolf Redux]

We are all familiar with the idea that, for much of the Age of Mammals, there have been large, scary cats with enormous teeth. They died out relatively recently, and as a result, we know a fair bit about them, and they remain one of the most popular prehistoric mammals with the general public - although mammoths do pretty well, too.

But, while the sabre-tooth cats stalked the world, what were the dogs like?

Perhaps the best known prehistoric dog is the dire wolf (Canis dirus). Do a google image search for "dire wolf" and you'll find far more images than you will searching for "sabre tooth", let alone something more specific like "Smilodon". But a look through those images gives you some idea why, and it doesn't have much to do with real-world fossils. The term "dire wolf" has been co-opted by fantasy fiction and games, and many of the pictures show the animals as they appear in Dungeons & Dragons, World of Warcraft, or Game of Thrones. They are generally portrayed as immense wolves, at least the size of a small horse, and sometimes with sabre teeth of their own, or bizarre spikes on their bodies.

Should I Stay or Should I Go?

Although they are hardly alone in this, mammals are noted for their care of their offspring. Yet many of them are solitary animals, and the young leave home as soon as they are able to survive on their own, so that the only groups seen are when a mother is caring for her children. But, of course, many mammals live in herds, packs, or other groups, with at least some individuals staying with their parents once they grow up.

But, even in herds, some animals do leave home, to establish or join new groups elsewhere. How do they make this decision as to whether to leave or stay? For many, its a fairly simple rule: the males leave, and the females don't. That means that a herd or other group is dominated by a core of females descended from a single matriarch, while the males have generally come in from outside. Initially, in most cases, the males wander about looking for a new group, perhaps together with one or two other young males in a similar situation, until they eventually find someone that will take them in. This ensures that they don't end up mating with their own female relatives, and keeps the gene pool as wide as possible.

The Bone-Crushing Dogs of Oregon

Aelurodon, a borophagine dog

The mammals are an ancient group, far older than the birds, and, by certain definitions, as old as the reptiles. But the true rise of the group - the period often called the Age of Mammals - only begins with the extinction of the dinosaurs, 65 million years ago.

But 65 million years is an incredibly long time. In comparison, mastodons and sabre-tooth cats both died out round about 10,000 years ago, not even 0.1% of that great timespan. Over the course of those millions of years, many groups of mammals (and, of course, of other animals, too) came and went, and the faunas and landscapes of the world changed time and time again. If sabre-tooth cats prowled the countryside just a few thousand years ago, you can see that you don't have to go back very far to find a world that looks, in many respects, quite different to that of today, and the further back you go, the greater the differences become.

For example, compare Africa and North America today. Africa has lions, elephants, leopards, dozens of different kinds of antelope, rhinos, hyenas, giraffes, hippos... the list of large and cool-looking animals just goes on. North America, while not truly impoverished, has far less in comparison. There's pronghorns, a few types of deer, three bears, wolves and pumas and, in terms of big animals, not a lot else. But it used to be like Africa just a few tens of thousand of years ago, never mind millions. America had elephants - or at least mastodons - along with many more large and fierce cats, and plenty of odd-looking antelope like creatures, and more besides. If you could go on a safari trip to the North America of millions of years ago, there would certainly be plenty to see.

This 65 million year span is conventionally divided into seven epochs. The last of these, in which we currently live, only starts with the end of the last Ice Age around 10,000 BC, and is therefore so short that you can't even see it on the chart I've used here. Most of the others are so long that they need to be divided into much shorter chunks for them to be of any real use when we try to get a picture of what appeared when.

The Miocene is the fourth of these epochs, and its name means "less recent" because there were less familiar looking animals alive then than in the three epochs that follow it. It is, in a sense, the last epoch before the sorts of animals we see today began to really gain a foothold. One illustration of the way that this happened is the story of the dogs, and a recent review of local fossils by Eric Ekdale and Timoty Rowe of the University of Oregon provides a snapshot that feeds into the bigger picture.

Oregon today has coyotes, wolves, and two species of fox - the red and grey. The wolves have only recently returned to the state, and are still struggling to gain a foothold, but the other three species are reasonably secure. Like all living dogs, all four of these animals are true "canines", in the true technical meaning of the word (which includes foxes, which, in more common parlance, we would call "vulpines"). But these are not the only sort of dogs that have ever lived.

"True"     "True"
 Dogs      Foxes        Borophagines
  ^           ^              ^
  |           |              |
  |           |              |         Hesperocyonines
  -------------              |                ^
        |                    |                |
     Canines                 |                |
        |                    |                |          Bears,
        ----------------------                |           etc.
                  |                           |            ^
                  |                           |            |
                  -----------------------------            |
                                |                          |
                          (First dogs)                     |
                                |                          |
                                ----------------------------
                                             |
                                             |            
             
The group of "true" dogs (technically "canins" - note the missing 'e') includes the grey fox, among others that we traditionally think of as foxes. The red fox of Europe and North America really is a fox, though!

As the chart above shows, the canines - modern dogs and foxes - lived alongside the borophagines ever since both groups diverged from the more primitive hesperocyonines at around the end of the Eocene. During the Miocene, however, the borophagines were by far the dominant group, with there being (so far as we know) relatively few species of true dogs or foxes around at that time. The fossils in the review date from around 10 million years ago, just as the balance was starting to switch, and the borophagines began to go into decline. The hesperocyonines had already gone by this point, apparently out-competed by their relatives during the previous Oligocene epoch.

I've mentioned before that many fossils are very incomplete, and give scientists very little to go on. This was the case with many of the fossils in this review, which included five teeth, one foot bone, and one leg bone, all from different animals. The researchers were fairly confident that these all belonged to borophagines of some sort, but had no way of saying any more than that. For example, one tooth was a premolar. It was the wrong shape to belong to a cat, too well-developed to belong to the only other sort of large carnivore around at the time, and too large to belong to any sort of fox. That only leaves the borophagines, but beyond that, who can say?

Another pair of teeth, however, both seemed to come from the same animal, and had been described as belonging to a fox (Vulpes sp) in a previous study back in the 1960s. The authors of the review thought that that was a bit over-optimistic, not least because that sort of fox isn't thought to have appeared for another three million years. They do agree, however, that it isn't a borophagine, and therefore is a true "canine" dog. Although there's not really any way to know, it might have belonged to Leptocyon, which lived across much of North America at this time. Leptocyon was smaller than a red fox, and slightly larger than a kit fox, and probably looked quite like both of these animals.

Its significant that these remains were the only ones that belonged to something resembling a modern canine. With so many borophagine specimens, its may be that this animal - whatever it was - was rarer than they were, confirming the story that it was the borophagines that were the top dogs of their day.

The other three fossils all belonged to different species of borophagine. That means that, 10 million years ago, like today, Oregon had at least four species of dog, although there's every chance that there were more we don't know about. The most complete fossil belonged to a coyote-sized animal called Carpocyon, that had previously not been found this far north and west. Unfortunately, it was missing the skull. Palaeontologists like skulls; they're usually the most distinctive bit of an animal, and in this case, it meant that we can't tell exactly what sort of Carpocyon it was - there are at least two possibilities.

It's the other two animals that really show how the dogs of modern Oregon are no match for those of ten million years ago, and they're also the only ones we can identify the exact species of. One, Epicyon saevus, was perhaps about the size of a rottweiller, but the other, its close relative, Epicyon haydeni, was a really, really, big dog. It was larger than a black bear, and had powerful, bone-crushing jaws that could presumably have demolished the entire carcass of anything it ate, skeleton and all. Unlike Africa, North America never had hyenas, but it had the great pack-hunting Epicyon haydeni instead, which lived in the same way and was considerably larger.

It must have been one of the most fearsome predators of its day, and it's hard to imagine anything would have chased it away from a kill, except possibly a sabre-tooth. Apart from the large size, it probably looked more like a wolf than a bear or hyena, but was surely a muscular and impressive animal. These are the animals that once terrorised the wilds of Oregon.


[Picture from Wikimedia Commons. Cladogram adapted from Wesley-Hunt & Flynn, 2005]

Surviving on the Edge

The spread of humanity across the globe has been bad news for a number of animal species. Species have always gone extinct, as the climate or other circumstances change, but the pace of extinction, and the number of species that are currently teetering on the brink has greatly increased over the last few thousand years. In many cases, humans are the direct cause of the problem: we kill animals for food, for sport, for make-believe medicines, to protect our livestock or crops, and so on.

But just as often the effects are indirect, as natural habitats are broken up into smaller isolated pockets or destroyed altogether. A few species have adapted well to human environments, and are rarely, if ever, found far from our settlements - the house mouse and the pigeon are both examples, before we even begin to look at pets or livestock. But most have not fared so well, and the question of how our destruction of the habitat affects animals is obviously an important one in conservation.

Wolf or Jackal?

This one really is a golden jackal

A species, you may have been told, is a group of animals that can breed with each other, but cannot breed with other species to produce fertile offspring. So wolves and domestic dogs are the same species, because they can interbreed, while horses and donkeys are not, because mules are infertile. There are a lot of problems with this idea, because it turns out that nature isn't really all that neat and tidy. For example, polar bears are quite clearly not the same thing as grizzly bears, but the two can produce fertile offspring - something that is happening increasingly as the polar ice caps melt and the natural habitat of the polar bears shrinks.

Its also not at all obvious how you're supposed to apply this definition to animals that don't reproduce sexually (though that's obviously not a problem with mammals). And what about those cases where two species have separated so recently in the evolutionary past that some individuals can crossbreed, but others can't? The classic example here are the herring gulls and lesser black-backed gulls, where the Siberian populations of these two species can interbreed, but the British ones can't. It really does get messy very quickly.

Even if it wasn't for all this, if we really did use the fertile interbreeding definition, how useful would it be? Well, we would have to accept that polar bears are really just odd-looking brown bears, for a start. But more than that, what about other species? Are we really going to try and cross-breed every plausible combination to see what happens? It can be hard enough to get some animals to breed in captivity at the best of times, making the whole idea completely impractical.

Inevitably, this means you sometimes have to end up applying some common sense, and describing something as a separate species largely because it's useful to do so. So polar bears, for example, are considered a species, because they are different in so many ways from brown bears. At the opposite end of the scale, there are many species that don't generally interbreed, but are so closely related that they look almost exactly the same, making it really hard to tell where one species starts and another ends. A lot of these are mice of various kinds, but it's also true of dogs.

The wolf (Canis lupus) is a very widespread species. Before humans drove it off from many parts of its range, it was found throughout Europe, and in most parts of Asia and North America. Human intervention brought them to Australia, in the form of dingos, and the domestic dog is also considered a subspecies of wolf. They once used to inhabit the southern coast of the Mediterranean, but now wild wolves are completely absent from Africa. Or are they?

The closest living relative of the wolf is the golden jackal (Canis aureus). Golden jackals are found in the Balkans, and across Arabia and southern Asia, but they are also found across northern and eastern Africa as far south as Nigeria. It would seem, therefore, that the golden jackal is more suited to these hot climates than its more northerly cousin, the wolf.

Wolf      Golden     Coyote    Ethiopian
          Jackal                 Wolf
  |          |         |           |
  |          |         |           |
  |          |         |           |         Other
  ------------         -------------        Jackals
       |                     |                 ^
       |                     |                 |
       -----------------------                 |          Dhole
                 |                             |            |
                 |                             |            |
                 -------------------------------            |
                                |                           |
                                |                           |
                                -----------------------------
                                              |
                                              |

Like the wolves, golden jackals are a varied bunch, with several different subspecies recognised. Indeed, one subspecies, found in Egypt, is quite hard to tell apart from a wolf - were it not for the fact that, officially, there are no wolves in Egypt. There had been some dispute in the past as to the exact status of these Egyptian animals, but, more recently, some very wolf-like jackals were also spotted much further south, in Ethiopia. Were they really jackals, as the textbooks said they had to be, or were they something else?

You can't just capture them, breed them with wolves, and see what happens. Not least because we know that wolves can breed with coyotes without any difficulty, and they're certainly a different species, so fertile offspring produced in captivity wouldn't prove anything either way. To see what they really are, we need to look at their genetics. If two groups of animals regularly crossbreed in the wild, their genetics should be very similar, and we have as good a reason as any we can come up with to say that they're really the same species.

So that's what the researchers did. They collected samples of the animals' dung, sequenced their DNA, and compared it with samples taken from jackals in Egypt, with wolves and golden jackals from a range of locations, and, for good measure, from seven other species of the dog family. (Including foxes - when you're doing this sort of test, you need to include something that's sort-of-similar yet manifestly not the same, just to make sure it's working properly).

Of course, they didn't analyse the entire genome, since modern technology isn't up to making that at all routine. Instead, they looked at a particular gene, cytochrome b, which is used as a standard in these sorts of studies. It's presumably not perfect, but with everyone using the same gene, at least it is possible to compare results with those from other workers, and this particular gene has done a good job so far at figuring which mammals are related to which other mammals.

The results showed, firstly, that these Ethiopian jackals were almost identical, genetically, to the ones seen in Egypt. This alone is significant, since it means that this subspecies is found much further south than previously thought. But it also showed that these animals were more closely related to wolves than to other golden jackals. Indeed, in some respects, they were more similar to wolves from places like Canada and Sweden than they were to wolves from the Himalayas.

So, whatever these animals are, they can't possibly be golden jackals. It appears that they diverged from the main group of wolves after the Himalayan wolves did, which means they have to be wolves, too. All the textbooks say there are no wild wolves in Africa, but we now know that there are - at least in Egypt and Ethiopia, where they have been living alongside golden jackals, and looking so similar that few people could tell them apart.

This is exactly the sort of problem that occurs when you have very similar looking species living side by side. Indeed, this sort of finding crops up quite often with mice, with nobody much noticing (or caring, frankly). But even then, is this animal actually a subspecies of wolf, or something else entirely? Just a few years ago, it was argued that Himalayan wolves were themselves a separate species. If that's right, then the Ethiopian animals might well be a species of their own, too - one we didn't previously know about. It's debatable either way, since they do seem to be much closer to northern wolves genetically than we'd expect a new species to be, yet different enough that a blood test will tell them apart.

Does it matter, though? Do we care whether this is a species or a subspecies? Well, funnily, enough, yes it does make quite a difference. Wolves are not an endangered species (and neither are golden jackals), so if these animals are a special sort of wolf, they will get relatively little protection from the various international conventions about such things. But if they're a species, then there's pretty good reason to suppose they might be endangered - there certainly aren't very many of them, and the local farmers do have a habit of killing them to protect their livestock. That's not a problem (from a species conservation perspective) if they're also found elsewhere in the world, but if this is the only place the species is found, then they can get protection under international law.

Considering that we can't come up with a good definition of what a species is, it makes a heck of a lot of difference whether a group of animals is one or not.

[Picture from Wikimedia Commons]