Sunday, 31 August 2014

The Jungles of British Columbia

It's changed a bit since...
Earth's climate has changed dramatically over the billions of years of its existence. The recent warming events may be unusually fast, but they are by no means unusually large. Not much more than 12,000 years ago the world was in the grip of the Ice Ages, when the polar ice caps stretched much further than today, and places like southern Italy and northern California were cold, sparsely forested steppeland.

On the other hand, there were times when the world was much hotter than today, warm enough that there appear to have been no ice caps at all, even at the poles. During the Age of Mammals - the eon of time since the extinction of the non-avian dinosaurs - the hottest of these was the Eocene Climactic Optimum. This took place a little over 50 million years ago, and it lasted rather a long time, punctuated by short periods of even greater heat. (That's 'short' as in they lasted tens of thousands of years, but not millions).

The world was a very different place back then. For a start, the continents weren't yet in their present positions, but also, of course, there were different animals around. This is, after all, over three-quarters of the way back to the time of T rex and its ilk, and there were a great many things that hadn't yet had time to evolve. It's well before, for example, the first members of the modern group of carnivorans appeared, and its not far off the time of the very first fossil representatives of some major groups, such as bats and cetaceans.

Much of what we know of the animals of this era comes from fossils found in what are now the relatively hospitable mid-latitudes. In recent years, there have been a number of finds up near the poles, in what would, at the time, have been a very odd environment to human eyes - no icecaps, but still with all that 'midnight sun' and 'perpetual night' business at the appropriate times of year. To get a complete picture, though, we also need to fill in the gaps, and that's where some recent research at a site near the town of Smithers in Britsh Columbia comes in.

Back in the early Eocene, the site in question was the location of a large lake, the northernmost of a string of lakes running down as far as northern Washington state. Now, as I mentioned, the continent has moved since then, so the lakes weren't at the same geographic coordinates that the shale deposits they left behind are now. However, North America was moving more or less due west at the time, still in the process of creating the Rocky Mountains. Which means that, so far as we can tell, while the longitude and altitude were different, the latitude of the area was pretty much what it is now. So we're in the general vicinity of 55° N.

The ancient lake beds have been studied before, and they've yielded a number of animal fossils. Mostly of fish, which is perhaps unsurprising, but we've also found quite a lot of insect fossils. In terms of mammals, we're rather more limited - some teeth from an early rhino-like animal called a brontothere, some more from a vaguely rodent-like animal with no close living relatives, and, possibly, a small bit of a hedgehog that has subsequently been lost. There have also, apparently, been some bird fossils discovered there, but they've not yet been officially described, so what kind of birds they were, I don't know.

So the discovery of two new mammalian fossils nearly doubles what we have. They both consist of no more than sizeable chunks of the animal's jaw, not the fully articulated skeletons that one often imagines fossils as being, but that's enough to give us a good idea of what they belonged to. Which is what we need for working out things like the ecology of the area.

By far the larger is the lower jaw of a tapir-like animal. To tell exactly what it is we'd need some other parts of the skull, especially the bits around the nose, but it is the right size and shape to belong to Heptodon, an animal known to live elsewhere on the continent at the time. And, even it isn't, it's probably a close relative, and the mere fact that it's a tapir at least tells us something.

Technically, perhaps, Heptodon is not really a tapir, in that it's just about different enough not to be placed in the modern tapir family, but it's so closely related to that family that there really isn't a better word for it in everyday English. It was, we think, about as large as a spaniel, and it probably didn't have the proboscis that modern tapirs do, but, beyond that, there was likely a fair degree of similarity.

Which is significant, because we think of tapirs - even fossil ones - as the sort of animals that only live in dense forests. Denser forests, that is, than the ones you'd find in northern British Columbia today. Indeed, as it turns out, we can check on whether or not this was different back then. That's because, in addition to the animal fossils I've already mentioned, there are lots of plant fossils from the area, showing what grew around the lake. And they show - as do all those insect fossils - that 52 million years ago, when this tapir lived, British Columbia was covered in jungle.

Well, okay, so one that wasn't much like a modern jungle - it wasn't tropical rainforest, or anything like that. It wasn't that much warmer at the time. In fact, the temperature doesn't seem to have been that different from that of modern London or Seattle. Which is around 5°C (10°F) warmer than it is now, but isn't exactly what you'd call tropical. The plant fossils indicate that common trees around these ancient lakes included things like cedar, pine, oak, and alder.

And yet this wasn't the sort of mixed broadleaf-coniferous forest you'd commonly find today. Perhaps partly because of the high rainfall (again, Seattle is a good analogy here, although not London, which is far too dry), the forests here were exceptionally lush, with the sort of diversity of insects and plant life that you'd expect to see in the tropics today. So it was pretty much like a jungle, albeit a jungle with oak and pine trees in it. Ferns seem to have been particularly dense, perhaps because they grew around the lake margins where sunlight could get between the trees.

The other fossil consisted of part of the upper jaw of a very small hedgehog. (Or at least, a member of the hedgehog family; we don't know if it was actually spiny). In this case, there was enough to identify the species, and it turned out to be one that nobody had seen before. It has been named Silvacola acares, which translates as "tiny forest dweller", and we're probably talking something about the size of a particularly large mouse. It's the only North American hedgehog of its age known north of Wyoming, and suggests that the animals were more widespread at the time than we'd thought.

But it's perhaps the tapir that's more significant. Clearly there was more to the jungle-like diversity of the local forests than just the climate, or the Seattle area would look like that today. But its presence does show that prehistoric tapirs cared more about the diversity and richness of their forest habitats than how warm they happened to be, and adds to the picture of Eocene British Columbia as a very different place than the home of the mountainous pine forests of today.

[Photo by Mark Kortum, from Wikimedia Commons]

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