Saturday, 30 March 2013

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.

Saturday, 9 March 2013

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?

Sunday, 3 March 2013

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.