The Strangest Marsupial?

So, I finally reach the end of the mini-series on mole-like mammals. I've looked at the moles themselves, two different kinds of mole rat, and the golden moles of Africa, and that leaves just one group. But its perhaps both the strangest and the least studied of them all.

As you can see (sort of) from the picture, these animals look remarkably like the golden moles. There's probably a good reason for that; like most golden moles, they burrow their way through dry, sandy soils, and they have a very similar lifestyle. Yet, apart from both being mammals, they are entirely unrelated. These animals dig through the sands, not of Africa, but of Australia. For these are the marsupial moles (Notoryctes spp.)

The marsupial mole family contains just two species, imaginatively named the northern and southern marsupial moles. They're pretty much impossible to tell apart just by looking at them, and for a long time it wasn't clear that they were two separate species at all. They live only in the deserts of central and north-western Australia, where they like especially sandy soils, and feed primarily on ants and termites.

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.

Badger Badger Badger

The European badger (Meles meles) is a very familiar animal across Europe, the animal we immediately think of when we think of "badgers". Its distinctive black-and-white face markings make it instantly recognisable, but, in fact, it has quite a range of different appearances, with variations in size, fur colour, and skeletal anatomy that allow it to be divided into a number of subspecies. This variation has been the source of some confusion when it comes to separating this species from its closest relatives.

It used to be thought that the European badger could be found throughout almost the whole of Europe and Asia, avoiding only the tropics, deserts, and the depths of Siberia. As a result it was called, quite reasonably, the "Eurasian badger". Over the last decade, that view has changed. Firstly, it became clear that the badgers of Europe and Asia were different enough to be considered separate species, and then that the badgers of Japan were likely different from those elsewhere in Asia. The suggestion has a venerable history; it was first made in the 1840s, but subsequently ignored when scientists decided that Eurasian badgers were really just one species that happened to be quite variable in appearance.

How Black Bears Trekked to Ontario

Can you show me the way to Ontario...?

The Pleistocene is the geological epoch immediately before our own. It ended just ten thousand years ago, a time so recent on a geological timescale that the modern epoch isn't even visible on the chart of the Age of Mammals shown below - its effectively just the line at the very top of the column. It's hardly surprising therefore that, for the most part, the animals alive in the Pleistocene are the same ones that are alive now, barring those that have gone extinct over the course of human history.

The Pleistocene, however, represents the Ice Ages, when vast glaciers covered much of the landmass of the northern hemisphere (rather less so in the south, though, because Australia and Africa, in particular, don't get as close to the south pole as Europe, Asia, and North America do to the northern one). It ends with two events that occurred roughly at the same time: the warming of the world at the end of the last Ice Age, and the dawn of human agriculture. In the case of North America, humans only arrived at the very end of the Pleistocene, meaning that it represents the last time that the continent was untouched by human hands.

Swimming in Sand: the Golden Moles

As we've seen with the moles and the two types of mole rat, spending one's entire life underground requires a number of unusual adaptations. However, because it has the great advantage of making you difficult for predators to find, it is a lifestyle that has evolved more than once among the mammals - and there are also subterranean reptiles, and even amphibians. The moles and mole rats are the best studied subterranean mammals, but they aren't the only ones. There are a lot of animals we could consider to fit this description, depending on exactly how broadly we want to define "subterranean", but I'll conclude this mini-series by looking at just two, which, like the moles and mole-rats, include particularly extreme adaptations.

The first are the golden moles. They inhabit southern Africa, often in much the same areas as the African mole rats, but the two types of animal don't seem to compete much. That's probably because, while the mole rats are herbivores, the golden moles are carnivores, feeding off various invertebrates, such as insects, earthworms, and spiders. That obviously makes them seem more like the true moles, but, in fact, the two groups are really not related at all.

Indeed, they are about as far from the true moles as its possible to be, while still being a placental mammal. Exactly what their closest relatives are has been debated, but they're probably the tenrecs, shrew-like animals now found only on Madagascar, and some rather odd African animals with a remarkable resemblance to otters.

Golden Moles        Tenrecs      Otter-shrews
     ^                 ^              ^
     |                 |              |
     |                 |              |
     |                 ----------------           Elephant
     |                        |                    Shrews
     |                        |                      ^
     --------------------------                      |
                 |                                   |
                 |                                   |
                 -------------------------------------
                                  |
                                  |

There are at least twenty one species, most of which don't have particularly memorable names, but one of them was only discovered in 2000, so there's no particular reason to assume we've found all of them yet. The first genetic survey to figure out how the different species relate to one another was only conducted last year, and differs in a number of points from what we previously thought based on their appearances. This sort of thing isn't very surprising, especially when you consider that they all look pretty much the same anyway, so that we were relying on some fairly minor points of difference.

So what do they look like? As the name suggests, most species are golden in colour, and, of course, they all have the generally compact body form that truly underground animals all tend to. But, even ignoring the colour, they do look rather different from true moles. That's because they don't burrow in the same way. Moles have spade-like forefeet and very powerful arms, to shovel soil out of the way. Golden moles, however, have much narrower forefeet, that look more like picks than spades.

The forefoot generally has just two functional toes, each ending with a long claw, although those that burrow in sand have three or four. In addition to the claws, the animal uses its head like a wedge to force its way through the earth, something that probably helps in looser soil. But it also means that, even more so than moles or African mole rats, the animal's eyes are likely to get grit and dirt in them. So, like the blind mole rats, golden moles have tiny eyes - just 1% the size of the head - that are entirely covered in hairy skin, and likely to be useless for anything beyond merely detecting the presence of light. So far as I can tell, there has been no research on whether they can even do that much, although it would be a useful ability for an animal that is going to be much safer in the dark, so I'd guess it's quite likely.

Perhaps the strangest feature of the golden moles, however, are their ears. The malleus, or hammer bone, of the middle ear is, in many golden moles, truly enormous. Relative to their body size, some species have the largest mallei of any mammal - in extreme cases being somewhere between sixty and a hundred times heavier than you would expect. In most cases, they are heavier simply because they are bigger, with a huge spherical or elongated head, but in the desert golden mole (Eremitalpa granti), at least, the bone is also remarkably dense. All of this apparently helps them to detect vibrations in the ground, and even work out the direction they are coming from, so that they can run for cover in the very deepest parts of their tunnels.

Golden moles tend to dig relatively shallow tunnels, just beneath the surface. Indeed, in the case of the desert-dwelling species they are effectively swimming though loose sand, using their pick-like claws in a kind of butterfly stroke. The tunnels have to be shallow, because that's where all the tasty insects are, but they also dig much deeper passages for protection, and its then that they use their relatively normal-looking hindfeet to kick up molehills on the surface. In addition to those they use to hide from predators, such deep passages can also end in breeding chambers, or latrines, making it hard for other animals to scent their spoor or find their young.

They seem to breed whenever they feel like it, rather than having a defined breeding season, and to give birth to small litters of no more than about three pups. Like most subterranean animals, other than the African mole rats, they are solitary animals, leaving their mother's nest as soon as they can. At least some of them are adapted to survive at a wide range of temperatures, including the ability to lower their body temperature and hibernate, if it gets really cold - as it sometimes does, for example, in the Drakensberg Mountains.

Although the group as a whole is well-adapted to a range of different habitats, from sandy desert to sphagnum-covered swampland, many individual species have highly specialised requirements, and that puts them at risk from encroaching human activity. Five of the species are considered endangered, but two further species are known from only a single specimen each, which doesn't exactly bode well. Indeed, one of those, the Somali golden mole (Calcochloris tytonis) isn't even a complete specimen - scientists just found a bit of one in the pellet of a barn owl in 1964, and have never seen another since.

Leaving that aside, the most endangered species that we definitely do have information on is De Winton's golden mole (Cryptochloris wintoni), which inhabits coastal sand dunes in the Namaqualand strandveld of South Africa. Or at least, it did, because, despite having tried, nobody has seen one since the 1950s, and its habitat has been largely destroyed by diamond mines. Our lack of knowledge of golden mole genetics may mean there are more species than we have found so far, but our own activity may also mean that there are rather less.

[Picture from Wikimedia Commons. Cladogram adapted from Seiffert 2007.]

Second Time Mums - Luck, Fitness, or Callous Calculation?

Oddities such as the brown antechinus aside, unless they die young, most female mammals can expect to give birth to several litters over their lifetime. This is a useful strategy, ensuring that you don't put all your eggs in one basket, so to speak. However, as human mothers may have noticed, looking after young can be a stressful and exhausting task, especially in species where the male can't be bothered to help out (which is most of them). As a result, in the wild, raising a litter of young is not always as successful as it might be, and, at times, the mother doesn't even survive the experience.

In general, it seems that mothers raising their first litter of young are the least likely to manage; those who have done it at least once before cope much better. That might not sound very surprising, but consider that there at least three different reasons why this might be the case. Perhaps the most obvious is that they just aren't very good at it the first time round. That may be partly due to a lack of experience, but raising young is fairly instinctive for most species, so it could also be that older mothers are larger, and better able to survive the experience of diverting some of their food resources to their offspring.

But another possibility is that the mothers might be deliberately not doing such a good job the first time round. This explanation, which I also discussed for the brown antechinus, is "terminal selection theory". The idea is that it's sometimes better for the mother to lose a litter and live to breed again than it is for her to die raising the first one. As she gets older, the less likely she will have another litter anyway, and the less she has to lose by putting all of her effort into raising the current one (assuming that is, that your primary objective is to have as many healthy young as possible, which in evolutionary terms, it usually is). So, if you don't completely wear yourself out on the first litter, maybe they'll survive anyway, but, even if they don't, at least you'll get to grow bigger and raise more young in the future.

The third possibility is that some mothers are better than others. If the 'bad' mothers are going to die trying to raise young, its far more likely to happen on their first attempt. If this theory is right, the only reason that older mothers do a better job of raising young is that they've proven they're good at it - all the bad mothers are already dead. They survive to raise more young, not because they were lucky, but because they have some advantage that continues to stand them in good stead as they age. Finally, of course, we should acknowledge that there's no reason why there can't be some truth in all three of these options, or that some might be more important for some species than others.


The northern elephant seal (Mirounga angustirostris) is one of the largest of all seals, with the adult males reaching over two tons in weight. They breed along the coast of California, spending the rest of the year offshore and travelling at least as far as southern Alaska. They belong to the true seal family, which is to say that they don't have visible ears or the ability to waddle about on land as fur seals and sea lions do; their hind legs are so well adapted to swimming that they can't be used for much else, and they have to drag their bodies with their front flippers when out of the water. Their closest relatives all live in Antarctic waters, from which the ancestors of the northern elephant seals probably headed north about three million years ago.

Leopard Seal   Crabeater     Northern        Southern
    etc.         Seal      Elephant Seal   Elephant Seal
     ^             |            |                |         Monk
     |             |       (move north)          |         Seals
     |             |            |                |           ^
     ---------------            ------------------           |
            |                           |                    |
            |                           |                    |
            -----------------------------                    |
                         |                                   |
              (migration to Antarctic)                       |
                         |                                   |
                         -------------------------------------
                                          |
                                          |
 
Interestingly, monk seals today are found in only two locations - the Mediterranean and Hawaii, which aren't exactly noted for being close to each other. Since seals as a whole seem to have originated in the North Atlantic, the Hawaiian ones must have travelled west by swimming in between North and South America, before they collided. Indeed, fossil monk seals have been discovered in the Caribbean, which would support this idea. For that matter, this is probably also the route that the Antarctic seals themselves took, much earlier, since we know of fossils of them from the Pacific, but not from the South Atlantic.


In a recently published study, Derek Lee of Dartmouth College in New Hampshire, looked backed over twenty years of records of northern elephant seals breeding at the Farallon Islands near San Francisco. There are a number of reasons why first-time elephant seal mothers might find it harder to raise their young than their more experienced relatives. Seals have to come ashore to give birth, but the rest of the time they are at sea. Since mating also occurs on land, it makes sense for it to happen at the same time, so they courtship takes place as soon as the previous litter are weaned, if not before. The rookeries where they breed become raucous and violent places with enormous males charging about all over the place, so the females can't afford to leave their young alone, which, since the males certainly aren't going to help, means they have to starve themselves for all the time that the pups are growing up.

This makes the life of a female elephant seal a pretty tough one, at least once they reach sexual maturity at three or four years of age. They spend eight months of the year pregnant, another two months raising a pup, and then two months stuffing themselves with food to make up for all the weight they have lost during their enforced crash diet. First time mothers, being smaller than their older relatives, would be expected to have a harder time surviving that catastrophic weight loss, and maybe also defending their patch of land and protecting their pup against aggression.

Its unsurprising, then, that first time mothers do not do as well than more experienced ones. They are less likely to raise their young to the point that they can be weaned and go off to live on their own, and also less likely to survive the experience long enough to return the following year. Not that this stops them trying; the study found that they were just as likely to mate after giving birth as experienced mothers.

Notice that, if this study is correct, it does rule out the possibility that this population of elephant seals, at least, are purposely expending less effort in looking after their first pup to increase their odds of raising a second or a third later on. If that were the case, while first time mothers would be less effective at raising young, they would be at least as likely to survive to breed again as experienced ones, and they weren't. So if they are trying to maximise their own survival at the expense of their pups, it clearly isn't working.

Its tougher to decide between the other two possibilities. Do experienced mothers do better and live longer because they got lucky the first time round, or because they have always been more skilled or fit than those which died? By examining the statistics, the study concluded that it was fitness as a mother, not sheer luck, that made most of the difference. Apparently, there is a Darwinian cull of unfit mothers, ensuring that only the best get to raise multiple pups in their lifetime.

The study doesn't end there, though, because it also looked at the effects of El Niño over the twenty year period. The main fish that northern elephant seals eat are Pacific hake, and, when El Niño brings its periodic warming of the eastern Pacific waters, the hake do less well, and the elephant seals suffer. Of course, hake aren't the only thing they eat; they are quite happy to consume squid, and even some small sharks and rays, but it is clear that the elephant seals do not put on so much weight in years when El Niño strikes.

We might expect that first-time mothers would do worst, especially if their smaller size is a handicap for them, but the study seemed to show that they did no better or worse than experienced mothers during warm weather. Which isn't to say that climate change, with increasingly warm waters and reduced numbers of tasty hake, doesn't affect elephant seals, just that it affects all of them equally, and that there are some things that being a good mother just can't help you with.

So, if you're an elephant seal, and you want to live long enough to have a second child, and more after that, you don't have to rely on luck, and you don't have to callously withhold all your energy from your first-born. Thanks to Darwin, you just have to be a good mother.

[Picture from Wikimedia Commons. Cladogram adapted from Fyler et al. 2005]

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]