Dolphin Snouts: The Long and the Short of It

A franciscana

On the whole, you would probably expect to find dolphins in the sea. This is, indeed, where the vast majority of them are, at least in the wild. But not all of them.

That's because there are also a small number of freshwater dolphins, living in particularly large river systems. Strictly speaking, though, only one of these, the Amazonian tucuxi, is really a dolphin, in the sense of belonging to the dolphin family. The others are slightly different sorts of animal.

There is, for example, a subspecies of finless porpoise that lives in the Yangtze River in China. You may, perhaps, recall that this river was also home to the baiji, a freshwater 'dolphin' that has recently been declared to be almost certainly extinct. (It is, incidentally, still waiting on formal confirmation of that fact, but it's hard to imagine that the outcome will be anything else).

The baiji, however, while related to the 'true' dolphins, was instead a slightly different kind of animal, one more adapted to a freshwater life. Apart from the baiji, there are also three more of these 'river dolphins', one of them living in the Amazon, alongside the tucuxi, one living in the Ganges and the Indus, and one that... um... doesn't live in rivers.

Caprines: Goats Among the Volcanoes

Japanese serow

While most goat-like animals today are grazers, subsisting on relatively large quantities of low-quality forage, it's thought that their ancestors were originally browsing animals, defending small patches of high quality food in otherwise inhospitable and craggy terrain. In the west, the most familiar surviving "resource defenders" of this kind are the chamois of Europe. While the exact evolutionary relationships of chamois aren't entirely clear, they are part of a broad cluster of species that is otherwise crammed with grazing animals, such as "true" goats and sheep.

Not so their counterparts in Asia, which form their own distinct evolutionary line, one that never appears to have given rise to true grazing animals. It is these species, not the chamois, that probably most resemble the ancestral goats from which all others evolved.

Is a Platypus a Mammal?

Yes.

Oh, you wanted more than that? Well, let's see what I can do.

I've been asked this question a couple of times recently, and I was somewhat surprised on both occasions. Yet why should I be? When I conducted a very brief straw poll at work this week, I discovered that most people I spoke to weren't sure, with all but one of those saying "probably not". (I had one response of "definitely not, because they're marsupials", an answer that's wrong on so many levels I'll ignore it from here on in). Only one was confident of the correct answer.

It's all very well for me to say "what else could it be?" because, if I'm honest, I spend a lot of time on this blog pointing out that porpoises aren't dolphins, rabbits aren't rodents, musk deer aren't deer, and so on. If a porpoise can be its own kind of thing, without being a dolphin, then why can't a platypus also be its own kind of thing - albeit at a higher level of strangeness?

Giving Birth While You're Asleep

A number of mammals living in temperate environments hibernate during the winter, or when food is otherwise scarce. The great majority of them are small animals, such as rodents, which normally have a high metabolic rate, and need to eat constantly to fuel their bodies. While hibernating, their body temperatures drop to virtually that of their surroundings - effectively making them temporarily cold-blooded. They do, however, have to wake up from time to time, if only to relieve themselves, and possibly have a light snack.

Bears, on the other hand, cannot really be described as "small mammals". Yet most of them do seem to hibernate. That hibernation is, however, rather different to what, for example, hamsters, are doing. In fact, it's sufficiently different that it's been argued that bears don't really hibernate at all. To be honest, it's a matter of definitions, of what exactly you consider the word 'hibernate' to mean. Today, most zoologists seem to consider 'hibernation' to be a perfectly good word for what bears are up to, although it's certainly possible to come up with a stricter definition.

Bats in a Changing World

Daubenton's bat is doing fine, thank you

After rodents, bats are the second largest order of mammals, in terms of number of species. Being small animals, they are also quite numerous in terms of their absolute population figures. Bats are found on every continent, except Antarctica, being among the few native placental mammals in Australia. Yet, despite this diversity, many bats are struggling to survive, with 14% of species worldwide being considered threatened, according to the latest (2008) edition of the IUCN Red List.

Now, in fairness, we do have to put that into a broader context. 14% may sound like quite a lot, and it is, in terms of actual number of species... but as a proportion, it's not unusually bad. It's about the same as for rodents, and considerably less than the 19% or so - nearly one in five - for all mammal species, worldwide. But still, bats are a fairly good indicator of how mammals in general adapt to the changing world around them.

There are a number of reasons for this that don't apply, for example, to rodents. Much of this has to do with their reproduction. Rodents and rabbits breed like... well, rabbits. They have multiple offspring, several times a year, that are themselves able to breed within months, or even weeks. This means that they can adapt rapidly to change; if it's a bad year, a lot of them will die, but the population zooms straight back up again if the next year is good. For bats, it's not quite so easy.

Caprines: Browsing Goats of the Western Mountains

Alpine chamois

The caprines as a whole can be divided into two groups, depending on which of two different lifestyles they happen to follow. The best known of these, since it is the lifestyle of sheep and "true" goats, is that of the grazing caprines.

Grazers feed fairly indiscriminately, munching down lots of grass and similar plants. In the case of the caprines, they survive in marginal habitats by eating pretty much anything that's available. They range across large areas in search of food, and adopt safety in numbers by packing themselves together in herds. Today, the great majority of caprine species adopt this lifestyle, and it's often what we think of when we think of goats and sheep.

But it appears that, in the evolutionary history of goat-like animals, it's a relatively recent innovation, one that was given a significant boost by the arrival of the Ice Ages. Before that, goats had adopted a rather different lifestyle, and there are still a minority of species - perhaps no more than five - that still live this way.

These apparently "primitive" goats were once grouped together in their own tribe, and given impressive sounding technical names like "rupicaprines" or "naemorhadins", but it's now less clear that they're really related. Instead, they represent at least two evolutionary lines within the goat-like animals, each a relic of the distant past when all goats were like this. Around them, some of their relatives switched to grazing, and, in the long run, proved the more successful.

Pleistocene (Pt 9): Before the Bison

Megatherium

The Pleistocene in North America can be divided into three 'land mammal stages', defined by the kinds of animal that inhabited the continent. The first, which was only recently added to the Pleistocene, is the one that comes before the Ice Ages proper, so that the Ice Ages themselves are, as I mentioned in part 8, divided into just two. As I said back then, the first of these starts with the arrival, not only of the ice, but also of the first American mammoths. The second, called the Rancholabrean after the famous tar pits, is much shorter, and essentially refers only to exceptionally bitter cold of the Last Ice Age. In terms of animal life, though, it is defined by the arrival of bison.

Today, when we think of America before the white man arrived, vast herds of bison are often part of our mental picture. And that, on the whole, is pretty much accurate, and is why their first appearance is deemed so significant in the ongoing evolution of North American wildlife. But what was the American wilderness like before there were any bison? What dominated the continent during the earlier, "Irvingtonian", stage?

As always, of course, the most common animals were the smallest. But, important though the teeth of (for example) voles are for the precise dating of geological deposits from this time, the eyes of any time travelling visitor would inevitably have been drawn to much larger animals. Obviously, mammoths and mastodons are a large part of the answer, and the presence of large elephantine animals crossing the plains would have been enough to tell our time traveller that, while he might still be in Kansas, it isn't really the same one he left. But there are many other beasts that would provide just as quick a clue.

Deer, peccaries, and horses are all examples of animals that aren't so unfamiliar today, although in many cases, the exact Pleistocene species were different from those alive now. Horses, for example, had, by this point, evolved to the modern single-toed form, but the last North American native horses died out around 12,000 BC, when the Pleistocene ended, leaving the ancestors of the domesticated forms behind in Asia. Exactly how many species of wild horse there were in America at this time, though, is unclear, with as many as fifty having been named - in my view, it's somewhat unlikely that they're really all distinct. There were, however, at least two broad types, one similar to the modern domestic horse, and the other, the so-called stilt-legged onager (Equus francisci, among others), which looked much more like a wild ass.