How Sloths Turned Upside Down

One of the things that sloths are noted for is spending a lot of time hanging upside down. This isn't, of course, something they literally spend their entire lives doing; they come down out of the trees to defecate, and they do sometimes travel over the ground - or swim across rivers - to move from one tree to another. They have also been observed, especially in zoos, casually sitting about in what we'd consider a fairly normal posture. But even so, being upside down is how they spend most of their time.

This is obviously pretty odd, from the perspective of a mammal (or, indeed, most other animals). You might think that what must have happened is that, at some point in the distant past, some ancestral tree sloth first headed up into the branches, decided to do so by hanging from them rather than by the more obvious method favoured by (say) primates, and that all of its descendants simply happened to do the same thing. In other words, it's a one-off quirk of evolution.

Except that can't be right.

The Smallest British Mammals: Shrews

Common shrew

For some reason that I no longer recall, a picture of a shrew cropped up while I was talking with a friend on the internet. "That's a mouse," she insisted. "No," I said, "it's a shrew." "Mouse!"

It was only later that I remembered that the German word for "shrew" is spitzmaus (literally "sharp/pointed mouse") and, since my friend was Austrian, she wasn't necessarily entirely wrong. From a certain perspective, perhaps to German-speakers, all these small, furry, long-tailed things are mäusen.

And it's certainly true that shrews do look, superficially, quite like mice. They tend to be smaller, with narrower snouts, and very small ears and eyes, but there is something quite mouse-like about them. Nonetheless, shrews (unlike, say, voles) are not rodents. In fact, as placental mammals go, they aren't even particularly related to rodents - humans are more closely related to mice than shrews are.

The Curiosity of Lemmings

The reason that there are so many different animal species in the world is that they all have different living requirements; it's no secret that a tiger has different needs from a hedgehog. In most land-based habitats, we can look around and see a fair variety of mammal species and it's obvious that, while they may compete in other ways (by eating each other, for example), they can all survive because they are using their chosen habitat in different ways.

But, in some cases, it's quite hard to find more than a handful of species - especially if we're going to restrict ourselves to mammals, and ignore all the birds, insects, and so on. This is often true of city centres, for example, where you may not have much aside from rats, mice, and urban foxes. But in the wild, however, we are typically talking about particularly marginal habitats, such as deserts, high mountains and other desolate wastes.

A Hole of Your Own

Many animals dig burrows for shelter, whether from the weather or from predators. In some cases these are complex or extensive burrow systems, such as we find with rabbits or gophers, and some animals, such as moles, try not to leave their burrows at all, adapting to a subterranean life. Most are much simpler than this, a basic hole in the ground in which the animal can rest securely at night - or during the day, as the case may be.

At the opposite extreme to the specialised diggers, however, are those animals that don't dig burrows at all, but still find it useful to seek shelter in this manner. These are creatures that will either use natural cavities or take over an abandoned burrow originally dug by something else. If they can't find one, it's usually not a disaster, although it may make life a little uncomfortable. But that's not necessarily true when it comes to time to breed.

Small British Mammals: Hares

Brown hare

The most visited post on this blog remains that explaining why rabbits are not rodents (their incisor teeth may look like those of rodents, but there are differences, and they have an extra set). I've also discussed, briefly, how rabbits manage to digest tough plant matter without the extra stomach chambers found in cows and similar animals by using the large bowel as a second stomach, and then eating the food twice.

All of these things are, of course, also true of the close relatives of rabbits, hares. There are two species of hare living wild in Britain, of which the more common is the European or brown hare (Lepus europaeus).  Like rabbits, they were only introduced to Britain during, or perhaps slightly before, Roman times, but they are now widespread across England, Wales, and Scotland.

Miocene (Pt 16): Giant Camels and High Llamas

One group of animals that you might expect to have done reasonably well as the climate dried out in the later stages of the Miocene epoch were the camels. Camels, of course, are not found wild in North America these days, but, back in the Miocene, it was the only place that they were found, having first evolved on that continent millions of years before.

Indeed, camels had been diverse in the Early and Middle Miocene, inhabiting a number of habitats that we would not associate with the animals today. Once those habitats changed with the shift into the Late Miocene, however, many of them failed to adapt, and a number of earlier forms died out. These included the stenomyline "gazelle-camels", the short-legged miolabines, and the floridatragulines, which had been adapted to the subtropical forests of the southern coasts.

Unravelling the Bushbuck

Imbabala

Three years ago, I wrote a series of posts on the various species of bovine. This was using 'bovine' in the wider, technical, sense than it's everyday meaning, essentially including all animals more closely related to cows than to sheep or goats. This obviously includes all the really close relatives of cattle - bison, buffalo, yak, and so on - but it also includes a number of animals that are more accurately described as 'antelopes'.

Most species of these 'bovine antelopes' belong to the genus Tragelaphus, collectively known as 'spiral-horned antelopes'. Especially if we include the large cow-like elands (sometimes given their own genus, Taurotragus) these are a fairly diverse range of animals, including some adapted to open woodland or savannah, and others adapted to dry scrub, mountain slopes, dense jungle, or swampland. Perhaps because it seems to be the most adaptable of the species, the most widespread of the spiral-horned antelopes is the bushbuck (Tragelaphus scriptus).