Sunday, 23 August 2015

Tuskless Walruses of Japan

There are a number of mammal "families" that contain just one living species. Of course, what constitutes a "family" of animals is an arbitrary distinction, rather like the one that says Pluto isn't a planet. So, really, all we're saying is that there are some mammal species that, in our subjective and pro-mammalian opinion, are do distinct and unusual that we feel they ought to be placed in a group all of their own. If they were insects, or snails, or something like that, we'd probably feel differently. But they're mammals, like us, so we don't.

One such family is the walrus family, containing - you've guessed it - the walrus (Odobenus rosmarus). Walruses are pinnipeds, which is to say, they are related to seals and sea lions. Just by looking at them, we can tell that walruses can walk on all fours like sea lions and fur seals, but unlike "true" seals, yet lack the external ears that sea lions and fur seals have and true seals don't. When you get to the interior structure of the skeleton, and so on, there are a number of technical differences that tell us that, no, this isn't just our imagination, they really are a bit different from all the others. And, there's, you know... the tusks.

Sunday, 16 August 2015

Hearing Through (Part of) Your Jaw

The skull of Diademodon, a 6 foot long cynodont
The most defining feature of mammals alive is that they give milk to their young. We can be reasonably sure that most fossil mammals that we know of did the same, but it's of no use for fossils at the very origin of the group. Neither are most of the other features that we might use to identify mammals today, such as the presence of sweat glands, or, given that the earliest mammals won't have been as water-adapted as dolphins, hair.

Instead, as I've discussed elsewhere, we have to pick a feature that survives in skeletons. Any decision we come to has to be arbitrary, and it's not going to line up with the very first point that mammals started giving milk to their young, since we don't know when that was. But one has to draw the line somewhere, and the one we've picked is the structure of the middle ear.

The mammalian middle ear consists of a cavity in the skull crossed by three tiny bones, connecting the outer ear (the visible bit, and the tube that runs in from it) to the inner ear, where sound is converted into neural signals that can be sent to the brain for interpretation. The first of these three bones is the malleus, or "hammer", which attaches to the inside of the eardrum at one end and to the second bone, the incus or "anvil", at the other. Finally, the incus connects to the innermost bone, the stapes, or "stirrup", which is attached, at its other end, to a particular part of the inner ear called the fenestra ovalis or "oval window".

Sunday, 9 August 2015

Of Moon Bears and Skunk Cabbages

One of the major debates in the study of human behaviour is that of "nature versus nurture". How much of what we do is the result of inbuilt tendencies and how much to the habitat we are raised in, including those things that we are taught? With non-human animals, the debate is, perhaps, less central, but there is still the question of inborn instinct versus learned behaviour.

Mammals being reasonably sophisticated animals, the possibility of some behaviour being learned - and moreover, of being learned socially, from other individuals, rather than by personal trial-and-error - is clearly one worth considering. For a great many behaviours in fact, there is going to be a bit of both; a mixture of instinct and learning.

For example, one of the things that most animals spend a large part of their time doing is searching for food. Much of the way that they do this is inborn. Cats, for instance, are born with the knowledge that anything that's small and scampering about is probably going to be tasty, and they instinctively know how to pounce on it, even if they have to practice to perfect the technique. On the other hand, social learning can also be important, both in determining what to eat, and where to find it. An example here is common marmosets, where the infants have been shown to avoid new and unfamiliar food unless an adult shows them that its safe to eat.

Saturday, 1 August 2015

The Dog Family: Foxes of Africa

Fennec fox
The fact that foxes will eat pretty well anything that's small enough has meant that some species have been able to colonise surprisingly harsh environments. The kit fox, for example, inhabits the desert shrublands of much of the western US, while Blanford's fox lives in the dry hills of the Middle East and south-central Asia. No fox, however, is more desert adapted than the fennec fox (Vulpes zerda) of North Africa.

Fennec foxes (sometimes simply called "fennecs") are also among the most distinctive of foxes. For one thing, they're the smallest wild members of the dog family, with particularly small adults as little as 33 cm (13 inches) in length, plus tail, and weighing just 800 g (28 oz.)  They have pale sandy-and-white fur, which is unusually long and soft - they even have fur on the pads of their feet, to give them some protection from baking hot sand. And, of course, there are the huge ears, quite out of proportion to the rest of the animal, which help to radiate away heat in an animal that would rather not lose too much water by panting.

Fennec foxes live across almost the whole of the Sahara Desert, from the Atlantic coast to the Nile valley. They are not typically found east of the Nile, where the closely related Blanford's foxes are found instead, but there are a few exceptions, and, for example, both species inhabit the Sinai. In fact, fennec foxes actually prefer the open sand dunes of the desert interior, an exceptionally harsh and arid environment.

Sunday, 26 July 2015

Pliocene (Pt 6): Attack of the Hyenas

Pachycrocuta brevirostris
Pliocene Europe was a continent as yet untouched by human hand - although, as I've noted, not of non-human primates. One might think that, in the absence of humans, sabretooth cats were probably the thing that other animals had to fear the most. There's probably a lot of truth in that, but they were far from the only carnivores in Europe at the time, and some of them were pretty fearsome.

On the other hand, there were also much smaller carnivores, too. At the bottom of the scale, weasels, badgers, otters, and martens already existed on the continent, and may have been quite common in the forests of the time. Foxes also survived the Zanclean Flood, and have continued living in Europe, right through the Ice Ages, up to the present day. In fact, Pliocene foxes would have looked remarkably similar to those of today, and are generally placed within the same genus, Vulpes.

Similarly, the largest carnivores of the European Pliocene would also have looked familiar. These were the bears, dominated by the gianr Agriotherium, which may have been slightly larger than a modern polar bear. Another woodland creature, it had perhaps been more common in the previous epoch, but survived throughout almost the whole of the Pliocene, dying out not long before the Ice Ages began in earnest.

Sunday, 19 July 2015

Greeting Old Friends

There are two species of chimpanzee currently recognised. Until recently, the common chimpanzee (Pan troglodytes) was by far the better known of the two. Today, it's probably fair to say, though, that the other species, the pygmy chimpanzee or bonobo (Pan pansicus), is well-known enough that when people say "chimpanzee" they often mean "as opposed to a bonobo", rather than referring to both species collectively. For clarity, I'm going to use the more specific term of "common chimp" for P. troglodytes in this post.

At any rate, being very closely related, the two species have a lot in common. (Neither, incidentally, is closer to humans than the other, in much the same way that if your aunt has two children, neither of those children is more closely related to you than the other). But there are also striking differences, particularly in the way that they interact with one another socially. A recent study, for example, shows that bonobos make eye contact with one another more frequently than common chimps do with their own kind. This is the sort of finding we would expect for an animal where social cooperation and coordination are all-important; in contrast, common chimps are more likely to focus on the mouth, and on whatever object their fellow is currently interested in himself.

Sunday, 12 July 2015

Bats in the City

Common pipistrelle
Many mammal species change the environment around them to suit themselves, whether it be by digging burrows or building beaver dams. Yet none has had an effect even close to that of humanity. Sometimes we reclaim land from the sea, or flood valleys to make reservoirs, but we also chop down trees to make room for agricultural land, and divide natural habitats with roads and railways. Arguably the most dramatic alteration we make to the landscape, however, is the construction of urban areas - an entirely new kind of habitat, unknown on Earth before our arrival.

Urban areas, are not, of course, entirely devoid of animal life. Many animals wander into the peripheries, and sometimes even into the centres, of our towns and cities. A general term for such animals used to be synurbic, but, over the last few years, this term has become more precisely defined, not to mean just any wild animal that is happy to live in urban environments, but those that actually prefer to do so. That is, there are more of them per unit area in cities than there are in the wild.