Sunday, 25 February 2018

The Pig Family: Wild Boar and the Domestication of Pigs

European wild boar
Generally speaking, the wild ancestors of agricultural animals have not fared particularly well. Wild goats are a threatened species, wild horses are an endangered one, camels are doing even worse, and wild cattle have been extinct for centuries. Wild sheep haven't done quite so badly, although they're hardly widespread, but, in general, one of the main problems facing such animals is that the sort of places they like to live are exactly the ones we want to turn into agricultural land to raise their domesticated kin.

Indeed, only two wild ancestors of widely domesticated herbivore are doing well: chickens and pigs. (This may, of course, depend on your definition of "widely"; I'm ignoring, say, rabbits). Indeed, the wild ancestor of the domestic pig is not only reasonably common, it's the single most widespread of any species of wild pig.

Sunday, 18 February 2018

Early Whales of the North Pacific

The majority of living cetacean species belong to a group called the odontocetes, or "toothed whales". Most of them aren't really what we' think of as "whales" at all, since the group includes all of the dolphins and porpoises. The group does, however, include a number of much larger species - some of them just really big dolphins, such as the killer whales, but others being less closely related, such as sperm whales, beaked whales, and narwhals.

The odontocetes as a whole stretch back far into the fossil record, with the oldest known examples dating back to around the dawn of the Oligocene epoch 34 million years ago. They rapidly spread across the globe, unhindered by the geographical barriers that often affect more land-based mammals. (The continents were all separate at the time, which would have helped, since it was possible to swim right around the globe without leaving the mid-latitudes).

Sunday, 11 February 2018

Jackals on the Motorway

Mammals tend to have a particular area in which they live most of their lives and conduct their various activities. This is known as the animal's "home range", and it's not quite the same thing as a "territory". That's because the latter is an actively defended bit of land, that the animal strives to keep clear of rivals, perhaps marking it with scent as a warning, and using aggression against intruders if they have to. The majority of mammal species don't bother to defend territories, but that doesn't mean that they don't have a home range - after all, they have to live somewhere.

One key difference between a territory and a home range is that the former, by definition, is not shared with any neighbours. Of course, the animal might be social, living in herds, packs or other kinds of band, so that all members of the group share a single territory, but, again, it's not shared with outsiders. A home range, on the other hand, almost always overlaps with at least some others used by members of the same species, especially if they happen to be of the opposite sex. Breeding would be problematic if they didn't.

Sunday, 4 February 2018

How Mothers Stop Their Daughters from Sleeping Around

Northern mole-vole (E. talpinus)
Generally speaking, mammals are equally likely to be born as either males or females. The exact proportion may vary a little, and it doesn't follow that both sexes form 50% of the adult population, because one or the other may be more likely to die young. It's even less the case that all males, or all females, are equally likely to pair up and have offspring of their own.

This disparity is known as reproductive skew, and it varies considerably between species, and sometimes even between populations of the same species. At one extreme, it's essentially zero. This happens if the species is basically monogamous, usually because child rearing is a sufficiently draining exercise that being able to share the duties between two individuals is really helpful. It can also happen for what might be regarded as the exact opposite reason - if the species is highly promiscuous so that the females will mate with absolutely anyone, once again, everyone's chances of reproducing are the same. There's just less of that courtship stuff to worry about, off-set by having a single-parent family once you're done.

Saturday, 27 January 2018

The Pig Family: Suids, Suines, and Swine

The pigs occupy an an interesting position in the mammalian family tree. The pig family, or Suidae, belongs to the order Artiodactyla, consisting of the cloven-footed mammals and a few of their closest relatives. (I will, at this point, note that I'm going to be using "artiodactyl" in the traditional, non-molecular sense, in this post. Paraphyly be damned, at least for today.)

This is unsurprising, given that pigs do, indeed, have cloven hooves. However, there are other features that almost all artiodactyls have in common, most significantly, that they are purely herbivorous animals with multi-chambered stomachs that they use to "chew the cud". Pigs, however, do not, and while they may not be the only non-ruminating artiodactyls, they are by far the most species-rich group to fit this description.

Traditionally, this was thought to be because they are more "primitive", having evolved before their relatives got round to developing more complex digestive systems. In a more modern way of looking at things, we'd instead note that, compared with other artiodactyls, pigs are omnivorous; they haven't developed more efficient ways of digesting tough plant matter because they don't need to. That they've survived as well as they have, evolving over many millions of years without ever being wiped out, shows that this has been a pretty successful tactic for them.

Sunday, 21 January 2018

Miocene (Pt 5): Hyenas in the Treetops

The first hyenas somewhat resembled this African civet
When we think of prehistoric carnivorous mammals, the first image that probably pops to most people's minds is that of sabretooth cats. It will therefore be no surprise that, were we to visit Middle Miocene Europe, one of the most widespread carnivores that we would find would be a moderately-sized cat-like animal with enlarged, serrated canine teeth in its upper jaw. What might be a little more surprising is that it wouldn't actually be a sabretooth cat.

The animal was called Prosansanosmilus, and it is known to have lived at least across what is now western Europe, from Spain to Germany. It, or its immediate ancestor, had probably first evolved in northern Africa, and arrived in Europe not long after that continent had collided with its northern neighbour - one of many animals to cross over as part of the so-called "Proboscidean Event". In life, it would surely have looked much like a cat, albeit with shorter legs and flatter paws less suited to pouncing and other rapid movement. But, in fact, it was not a cat, but a member of a family that, like the bear-dogs, no longer exists; that of the barbourofelids, or "false sabretooths".

Sunday, 14 January 2018

The Strong, Silent Type?

Compared with many other kinds of animal, mammals can often have complex social lives. While many kinds of mammal live in packs or herds, with sophisticated dominance hierarchies and the like, the most complex of all mammal societies (at least as defined by we humans) belong to species belonging to one of just three mammalian orders. It's likely no coincidence that these also happen to be the three orders with the proportionately largest brains.

Perhaps the most obvious of these are the primates, the group that includes our own species. Many species of monkey have flexible social structures where members join and leave groups, adjusting their social positions accordingly, and relying on sophisticated interactions with one another to keep everything functioning. However, the social lives of cetaceans (whales, dolphins, and porpoises) can be equally complex, with, for example, multi-level associations between different pods. The third group to exhibit this sort of behaviour are the elephants.

Sunday, 7 January 2018

Making Hay on a Mountaintop

As I write this, the weather across much of the US is not great. According to Google, it is, right now, -12°C (10°F) in Washington, DC, and that's ignoring the effects of wind chill. And it's a nippy 16°C (61°F) in Arizona... okay, so perhaps that latter one isn't the best example. But the point is, this is harsh, and, if it isn't fun for humans, then it isn't for wild animals, either.

Indeed, winter in general is a tough time for animals living in temperate climes, as much due to the lack of food resources as to the need to shelter from the cold. There are a number of different strategies they use to mitigate this time of enforced starvation. Some animals, of course, simply brave the conditions, using thick winter coats, and perhaps some means of digging out food from beneath a blanket of snow. But others take more active steps, and there are basically three ways of doing this. One is to hibernate, so that you don't need much in the way of food until the spring. A second is to simply move elsewhere, either migrating to warmer climes or, if you live on a mountain, just heading downhill a bit.

A third approach is to collect food in the autumn and then store it somewhere through the winter, so that you have ready access to it. This, naturally, poses a number of problems. You have to remember where you put the food, hope that somebody else isn't going to find and eat it, and ensure that it doesn't spoil. Even so, a number of smaller mammals do exactly this, and it's clearly something that works for them.