Caprines: At Last, The Goats

Wild goat

In English-speaking countries, and, for that matter, South America, sheep are a far more common sight on farms than goats are. (To be fair, in much of the US, even sheep aren't as common as they are in Britain, let alone Australia and New Zealand). However, while the worldwide population of sheep is, indeed, higher than that of domestic goats, it's not by as big a margin as you might think. In particular, goats are a vital mainstay of the agricultural economy in India, and throughout much of Africa.

The reason for this is their extreme hardiness. Adapted to living in habitats even more marginal than those of sheep - which, at least in their wild form, are themselves more resilient than, say, cows or pigs - they're ideal for raising in the sort of scrubby environments that you get in much of Africa and the Middle East. Even so, after approximately twelve thousand of years of selective breeding, the domestic goat has come a long way from its wild ancestors. They're often larger, with smaller horns, or none at all, and some have long, floppy ears. There are a number of different breeds, from milk-producers like Saanens and Toggenburgs, to the muscular Boer goats, bred for their meat, to the long-haired angora and cashmere goats that produce fine wool and mohair.

The First Placental Mammals

Shrews most closely resemble the ancestor
of all living placentals

I don't normally cover stories if they've had extensive coverage in mainstream media. I prefer to cover the interesting peculiarities that those outside the field are unlikely to hear about. But there's been a story recently that I'm going to make an exception for. Because, basically, I feel like it.

Last month, you may have seen a story about the origin of the placental mammals having been identified. Here, for example, is the BBC coverage. The study being discussed here, by Maureen O'Leary and co-workers, pinpointed the origin of modern placentals as around 65 million years ago. You might also recall a post I wrote in 2011, talking about the discovery of the oldest known fossil belonging to this group. That was 160 million years old.

What, you might wonder, the heck is going on?

Well, the first thing to point out is that the headlines of the two studies are not talking about the same thing. The new one is talking about the origin of the crown group of placental mammals, which doesn't necessarily mean all placental mammals ever. So what's a "crown group" when it's at home?

Caprines: Go West, Young Sheep!

Bighorn rams

As we've seen, the domestic sheep is descended from one of what may be quite a large number of related species native, broadly speaking, to southern Asia. Back in the Pliocene, however, long before those species separated from one another, one stock of ancestral sheep headed north, into Siberia. When the Ice Ages arrived, and sea levels dropped, these sheep were among several animals that headed... well, from their perspective, they were going east, but where they ended up was western North America.

Sheep, in general, inhabit high hills and rugged terrain in the shadow of mountains. They don't live on the cliffs and the impassable heights themselves, but they do like precipitous rocks nearby, so that they can flee into them at the first sign of predators. Given those requirements, western North America is an absolutely ideal place for sheep to be, and the descendants of those first colonists spread far and wide. However, while there's much argument about the exact number of wild Asian species of sheep, it's pretty much agreed that, in America, there are only two.

Probably the more familiar of these is the bighorn sheep (Ovis canadensis). It's also easily the more widespread of the two, and inhabits a surprisingly broad range of habitats, from the mountains of southern British Columbia and the hills of North Dakota down to Baja California and the Sonora Desert. That obviously includes both hot, scrubby, deserts and cold, damp, pine forests, as well as much in between. Indeed, aside from the insistence on rugged terrain that prevents them from reaching as far east as, say, Kansas or Nebraska, bighorn sheep don't seem to have much in the way of requirements.

Pleistocene (Pt 7): Meanwhile, Across the Atlantic...

Columbian mammoth
(It's likely that the real animal was hairier than the one in
this reconstruction, but it shows the tusks effectively)

Over the last five parts of this series I have described the history of Pleistocene Europe, describing some of the ways that the animal life of the continent changed over those thousands of millennia, and looking at a few particular animals in more detail. But one doesn't need a degree in zoology to notice that today, the wildlife of North America, for example, is different to that of Europe. North America has coyotes, raccoons, cougars, armadillos, and pronghorn antelope, to name just a few animals that are simply absent in Europe. (Or, in the case of raccoons, were absent until somebody made the mistake of releasing some of the furry nuisances in 1930s Germany).

It's hardly surprising that that continent also had different wildlife during the Pleistocene. One notable difference, for instance, is that we humans weren't there. Obviously, neither Columbus nor Leif Ericsson were genuinely the first person to discover America. But even whichever long-lost group of Native Americans was actually the first to discover the great western continent, they did so long, long, after the first Europeans discovered Europe. While Europe had at least some species of human inhabiting it for about two-thirds of the Pleistocene, nobody reached America until the epoch was all but over.

Tuco-tucos on the Edge

Flamarion's tuco-tuco (C. flamarioni)

There are a great number of endangered animal species in the world, and, as of the time of writing, 644 of them are mammals. These include, of course, such dramatic and visible animals as rhinos and pandas. But they also include many smaller, less glamorous animals. For example, over 200 species of rodent are endangered worldwide, and while that's not actually very many out of the total number of rodent species that exist, it's still quite high in absolute terms.

I realise, of course, that it's unrealistic to expect the public to get as concerned about obscure rodent species as they are about, say, endangered cats. Because, you know, snow leopards. But, in the semi-random style of this blog, inspired largely by whatever I happen to have seen in the literature recently, I want to talk about the social tuco-tuco (Ctenomys sociabilis).

For those who've not heard of them, tuco-tucos are a family of burrowing rodents native to South America. They look rather like voles, but are somewhat larger, at around 20 cm (8 inches) long, if you include the tail. They're good at digging, but they don't live underground in the same sense that moles or mole-rats do, since they leave their burrows during the day to feed on things like grass seeds. In fact, they've been described as the South American equivalent of gophers, although the two groups aren't really that closely related as rodents go. One of their distinctive features is their loose, wrinkly, skin, which apparently allows them to turn round easily in their narrow burrows.

Do Monkeys Get Divorced?

Panamanian night monkeys (Aotus lemurinus)

Probably the most common reproductive strategy in mammals is that of polygyny. That is, any given reproductive group consists of a small number of reproductive males - often only one - and a much larger number of females. There are various different ways this can be arranged. For example, males may leave the pack or herd when they reach maturity, wandering about on their own, or in very small groups, until they find a new pack that they can take over, getting all the females for themselves. Alternatively, there may be no long-lasting partnerships, with males and females living in separate groups for most of the year, and then males staking out patches of ground to attract a number of females to them for the duration of the breeding season.

Both of these situations lead to an inevitable conflict between males. If each male mates with several females, but females stay loyal to a single male (even if only for the season), a lot of males won't get a look in. There are strategies for some smaller males to get round this problem, but, in general, fighting is your best bet. And that means that male mammals are often larger than females, and with larger teeth, horns, antlers, or whatever else it may be that they do their fighting with.

But there are alternatives to polygyny. If females mate with lots of males, then male competition needs to work in a different way, whether by getting in first, or by producing more, and higher quality, sperm than your rivals. And then, of course, there's monogamy.

Caprines: Telling the Sheep from the Goats

Transcaspian urials
(Note that the rams of this species/subspecies have
particularly argali-like horns)

To most people, especially in the West, the most familiar member of the goat subfamily is probably... the sheep. Worldwide, domestic sheep are more common than goats, although not necessarily by as much as you might think. Goats are more popular than sheep as farm animals in places like India and Africa, but overall, sheep have the edge in numbers. That's probably no great surprise to those of you in most parts of Europe or America, and even less so if you're in Australia or New Zealand.

But perhaps I should back up there. Did I really just say that sheep are a kind of goat?

Well, yes I did. Kind of. Sheep are members of the goat subfamily, but really, they're goats only in the sense that ferrets are a kind of weasel. But why is it that way round at all?

The goat subfamily, or Caprinae, was given its name by the great Victorian zoologist John Edward Gray, quite early in his career, in 1821. From a scientific standpoint, there was absolutely no reason why he couldn't have named it the sheep subfamily, but instead, he chose goats as the best example of the group. I don't know his actual reasoning, but it certainly makes sense: far more members of the group resemble goats than resemble sheep. And so, from this, admittedly arbitrary, standpoint sheep are an odd kind of goat, and not the other way round.