Fossorial Fossils

Skeleton of a European mole
(Note the odd-looking humerus and shoulder girdle)

The mole family includes over 40 species, found across the Northern Hemisphere. They are, of course, most noted for living underground, burrowing their way through the soil in search of worms and similar food. But, in fact, this is by no means true of all members of the family.

Indeed, we can divide the lifestyles of these animals into three broad categories. First, there are the truly fossorial moles, meaning those that spend virtually their entire lives underground. This is the case for about three quarters of the living species, including the familiar ones that so annoy gardeners. But there are also the semi-fossorial "shrew-moles", that do quite a lot of digging, but spend much of their life above ground, retreating to their burrows primarily to sleep, and perhaps to supplement their surface diet. And, finally, there are a few species in the family that are semi-aquatic, spending their time swimming in rivers, even if they, too, have burrows to rest in.

It's generally thought that it's the shrew-moles that most resemble the earliest prehistoric members of the family. That, in other words, while moles may always have dug holes, the specialised features that allow them to spend their whole lives below the soil took some time to evolve. Which is probably what you'd expect anyway, especially since the closest relatives of moles alive today are the shrews and hedgehogs.

Monkeys in the Snow

When we're considering how an animal interacts with its environment, and the other life around it, diet is understandably one of the most important features we look for. That isn't to say that there aren't other important factors, too - what eats the animal, when and where does it sleep, how fast does it breed, does it physically alter its environment, and so on. But what sorts of things the animal eats is fairly high on the list.

But that's not always as simple a question to answer as one might like. If the animal is an extreme specialist, then it's not such an issue - it eats whatever it eats and that's that. But most creatures have at least some variety in their diet, and, in practice, not all of them will be eating exactly the same mix of foods. In most parts of the world, for instance, diet will change with the seasons. In temperate environments, different foods are available throughout the year, with fruits and seeds, for example, being most available in the autumn, and insects being more readily available in summer than in winter. Even in the tropics, there are usually wet seasons and dry seasons, which affect both the plant life and the creatures that feed upon it, which, in turn, affects the carnivores.

Then there are animals that inhabit different habitats across their range. Here, diet can be affected simply by where you happen to live. In turn, what, and how much, food is available can affect other aspects of the animal's behaviour. For example, it may affect how they interact with others of their kind, how big an area they need to forage in if they are to keep themselves healthy, and such things as birth rates and mortality.

How Not to be Eaten

This picture is far less cute if you're a mouse

Animals, on the whole, want to avoid being eaten. There are a number of ways of achieving this, including being well armed or armoured, or just being too large for most predators to bother with. For relatively small and inoffensive animals, however, we're left with being difficult to find, and being good at escaping when you are detected.

But even this can cover a range of different strategies, or combinations of strategies, not least because there are a lot of different predators out there, and what may be good for escaping from one may be less effective against another. Moreover, if every animal evolved to avoid, say, the open grasslands in favour of forest cover, then there'd be an awful lot of potential food out there going begging. Inevitably, something would evolve to take that risk. There's always a pay-off involved.

It's as a result of things like this that there are so many species of small mammal, with subtle differences between them that are not always obvious to the casual observer. To understand the predator-prey dynamics of a particular habitat, we really need to look at a whole range of creatures. So many, perhaps, that it's beyond our ability to easily analyse in its entirety, but we can at least take a stab at a manageable group of species in one particular place, trying to see what makes them different, and why what works for some does not always work for another.

The Dog Family: The Marks of Zorros

Culpeo

When North and South America collided towards the end of the Pliocene epoch a little over two million years ago, dogs were, for the first time, able to cross to the southern continent, a place that had previously been somewhat lacking in large mammalian carnivores. The dogs that crossed over all seem to have been related to wolves, rather than foxes. However, the fox body plan and lifestyle, with its high adaptability, proved so useful that most of the living descendants of these animals look just like foxes.

However, they are not "true" foxes, but rather, wolf-like animals that evolved into creatures that happened to closely resemble the members of the much older lineage that we find on the other continents (red foxes, Arctic foxes, the various kinds that we find in Africa, and so on). Recognising the distinction surprisingly early, some nineteenth century naturalists called them "fox-tailed wolves", and there has been a (largely unsuccessful) move to call the animals "zorros" in English, to distinguish them from the true foxes. That this didn't take off is perhaps due to the fact that "zorro" simply means "fox" in Spanish, and most of the researchers studying the animals are likely to be Spanish speakers... so it's not really a lot of help.

Pliocene (Pt 7): Home, Home on the Steppe

Mylohyus

The beginning of the Pliocene epoch in North America was not marked by any great cataclysmic event, such as happened in Europe at that time. Nonetheless, while we're not far enough back that North America is unrecognisable, or in a different place, or anything like that, there would have been clear differences if we could see it from space.

Perhaps the most obvious difference would be that the Great Lakes didn't exist yet, since they were carved out by the advancing glaciers of the Ice Ages - which have yet to happen. With sea levels higher, Florida (then, as now, not a place known for its mountain ranges) is largely underwater, and there were probably many other changes around the coast, too.

Arguably the most important difference, however, is further south. Mexico is not so different, at least in its general outline, but beyond that things start to change. Depending on the exact point within the Pliocene we're talking about, you could perhaps have walked as far as Nicaragua without getting your feet wet. Beyond that, however, the Central American peninsula tapers to a point, and where Costa Rica and Panama should be, there is nothing but a chain of tropical islands, a southern counterpoint to the much larger chain of the Caribbean further north.

A Forest Fit for Sloths

One of the main problems facing the continued survival of wild animal species across the world is loss of habitat. (Naturally, this goes for all kinds of animals, and plants, too, even if we're mainly interested in mammals here). As humans expand in numbers and push into the wilderness, we turn a lot of it into farmland to feed ourselves, use it for logging or mining, or simply build roads across it. The animals that are least concerned about this are those that we have domesticated, whether as pets or as livestock, with supremely adaptable generalists such as rats and pigeons following not far behind.

At the opposite extreme, of course, are the specialists, those that require one very specific sort of land to live in. In between there are a great spectrum of other animals, that can cope with some change, but not too much, that find orchards and plantations a reasonable substitute for forest, and so on. If we're interested in conserving particular animals, one of the first things we need to understand is just what their requirements are.

Even then, it's not enough to know that a particular animal "likes forests". What kind of forests? Do they really have to be primeval and untouched, or are there are at least some viable alternatives? Are there, perhaps, particular parts of the forest that they like more than others? In the grand scheme of things, just leaving stuff alone is probably the best answer from a conservation perspective, but, since human numbers aren't going to start falling any time soon, compromise is often inevitable. So the question then becomes: on what can we compromise?

A History of the Strange-Jointed Beasts

All living species of mammal fall into one of three major groups, representing the lowest branches of the mammalian family tree: the placental mammals, the marsupials, and the bizarre, egg-laying, monotremes. Well over 90% of identified living species fall into the first of those groups, which prompts the interesting question of how we divide those up - what, in short, are the next branches on the tree?

In the strict, old-style, system of classification, the next major level down is that of the "order", groups of broadly similar creatures that are in turn, divided into more than one hundred "families". Primates, for instance, are an order.

What the orders are, and how many of them there might be, has varied a little down the years, but nineteen or twenty would be a good, modern estimate. But, of course, the orders themselves are entirely arbitrary, and, even if they weren't, it isn't as if they all sprang simultaneously from the same stock. In evolutionary terms, there must have been some early branches in the placental family tree from which the "orders" that we know today descended.

The question of how to group the orders together into some higher level pattern is one that mammalogists have been been pondering for well over a hundred years. The problem is that the orders are pretty distinctive - is a moose more like a wolf than it is a monkey? When all you have to go in is physical anatomy, these are not the simplest questions to answer, and it's not surprising that people have come up with different answers.