Sunday, 24 July 2016

The Echidna's Incredible Expanding Testicles

The echidna is a pretty strange mammal. Most notably, it is the only mammal other than the platypus that lays eggs. I've discussed in an earlier post why that doesn't disqualify it from being a mammal, but it is undeniably unusual. It's not even the only odd thing about echidnas, since they can also sense electricity through their snout, and the males have a four-headed penis.

I'm not making this up.

There are, in fact, four different species of echidna. The one most people are likely familiar with, though, is the short-beaked echidna (Tachyglossus aculeatus), on the grounds that it's the only one found in Australia. (The others, if you're wondering, live in New Guinea). In fact, they're found pretty much across the whole of Australia, albeit generally in open woodland or rainforest, rather than true desert. Even so, that's a fairly broad range of habitat types and variations in climate, and their behaviour does change somewhat across the continent.

Sunday, 17 July 2016

Bovines: Mini-Buffaloes

Anoa (probably lowland species)
One of the themes that we see played out from time to time in evolution is that of insular dwarfism. Here, a population of some large animal is trapped on an island or (less commonly) some other isolated locale from which they cannot easily escape. Faced with a limited food and other resources, over sufficiently large periods of time, they become smaller, making the best of whatever there is. (There is also a related phenomenon of insular gigantism, whereby really small creatures become larger, likely because they no longer need to hide from predators that happen to absent on their island).

Today, there are no tiny elephants or rhinos, but bovines - where the males of some species can weigh upwards of a ton - are a different matter. At least two, and probably three, species of living bovine are examples of exactly this principle in action.

The reason that I'm vague about the numbers here is that there is still some dispute about the nature of the anoa. There are usually regarded as being two species: the lowland anoa (Bubalus depressicornis), and the mountain anoa (Bubalus quarlesi). But not everyone agrees that the two are distinct. The first formal suggestion that they might be separate species was made by Dutch scientist Pieter Ouwens, better known for being the first scientist to describe the komodo dragon. That was back in 1910, and at least as late as the 1960s, there was still general agreement that the two forms were physically distinct, and that they likely favoured different terrain.

Sunday, 10 July 2016

Fossilised Squirrel Brains

The fossils of mammals, and, indeed, other vertebrates, tend to consist largely of bones. That's not an absolute rule, of course, and occasionally other parts do fossilise, and there are also remains of things like footprints and poo. But, generally speaking, it's much harder to get an idea of the soft anatomy of a long-extinct mammal than it is of what its skeleton looked like.

There are many soft organs that we'd really like to understand the evolution of, but, while we can make inferences on other grounds, direct fossil evidence is always likely to fall short for most of them. The brain, however, is something of an exception, and this is perhaps fortunate, given the importance we tend to attach to it.

This is not to say, of course, that finding direct fossil evidence of brain structures in long gone mammals is particularly easy. But the brain sits inside the skull, and is fairly tightly wrapped within it. Which means that if we can get some idea of the shape of the hollow bit on the inside of a skull, we've got a pretty good idea of the shape and size of the brain it once housed. This has, in fact, been done for a number of fossil mammals, but, generally only of large ones. For smaller mammals, such as rodents, the evidence is much more patchy.

Sunday, 3 July 2016

The Importance of Monkey Grandmothers

Humans are almost unique among mammals in experiencing menopause a long time before their actual death. That is, they continue living for an extended period after they cease to be able to have children and pass their genes on to the next generation. Evolutionarily speaking, one might think, there is no longer any point to them; their task is done. But, obviously, that's not the case, as we can see from the importance of grandmothers and other female elders in, for example, tribal societies. For example, their greater knowledge of the world, and the ability to share in the childcare of their descendants, can mean that the latter have a better chance of survival.

Examples of this effect among other mammals are much less common. At the extreme, some mothers simply drop dead as soon as they have raised even a single batch of children to adulthood, but even among the majority of species, it's being a mother, not a grandmother, that's really important. Perhaps the best known exception is among elephants. Here, the leader of a family group is typically the oldest living female, who helps the herd through her knowledge of the outside world (where watering holes may be found in the dry season, for example), experience of predators, and a lifetime's worth of social knowledge.

Sunday, 26 June 2016

Bats v. Hawks

Bat hawk
There are not many animals that eat bats. Or, at least, that's often been the received wisdom. Bats only come out at night, fly through the air, where it's difficult to catch them, and many spend the day sheltering in caves that are difficult to access, and that rapidly become filled with so much bat poo that not much else is willing to venture within. But they don't all live in caves, they aren't the only things that come out at night, and, anyway, there's just an awful lot of them, so surely something must, in fact, eat them?

And, of course, the answer is "yes". In fact, there are actually quite a lot of animals that eat bats from time to time. In Brazil, for instance, snakes, especially tree-dwelling constrictors, have been reported to prey on bats. So do other vertebrates, from fish to mammals, and even a few invertebrates, such as, yes, really - giant centipedes. But, considering all that flying they do, it's perhaps unsurprising that the main predators of bats are, in fact, birds. And, among the birds, it's doubtless also not a great shock to discover that owls are the primary culprits.

For instance, it has been estimated that in Britain, at least 11% of all bat deaths (and probably more than that) are caused by birds. Around three quarters of those attacks are by tawny owls (Strix aluco), and 90% of all predation incidents on bats in Britain are due to owls of some kind. With 5% of predation incidents having nothing to do with birds at all, it nonetheless follows that a further 5% must be due to birds that aren't owls... and, of course, this is just Britain, where (for example) tree-roosting bats are quite rare.

Sunday, 19 June 2016

Bovines: Will the Real Buffaloes Please Stand Up?

African buffalo
Outside of North America, the term "buffalo" refers not to the bison, but to two (or more) species of bovine native to Africa and Asia. In the wild, by far the more common of the two is the African buffalo (Syncerus caffer), which has the distinction of being the only non-domesticated species of truly cow-like bovine that isn't even slightly endangered.

African buffalo are very numerous, and found across wide swathes of Africa south of the Sahara. This includes a fair number of different habitats, and African buffalo vary not just in their habits and preferences, but in their physical appearance, across that range. They were first described scientifically by Swedish naturalist Anders Sparrman in 1779, based on an animal found at Algoa Bay, near present-day Port Elizabeth in South Africa. Given the association with that general part of the world, the alternative name of "Cape buffalo" is often used for the animal, although that seems a little restrictive for something so widespread to me.

At any rate, over the next century and a half, scientists racked up descriptions of an impressive number of subspecies - by 1913, at least 21 were recognised. In the hundred years since, that number has steadily declined as it has become clear just how tiny the differences between some of them were. Even now, the question isn't entirely settled. There is agreement that there at least three subspecies, but there might be more, and it has been also been argued that some of them genetically distinct enough to be full species in their own right.

Sunday, 12 June 2016

Pliocene (Pt 11): A Profusion of Pigs

Probably the most numerous large mammals in Africa today are the antelopes, of which there are a great many species. In this respect, the Pliocene was not much different, with antelopes providing a large part of the diet of the various carnivores that lived before the Ice Ages, from lions and hyenas to sabretooth cats. However, the mix of antelope species was different then that it is now, not least because of the generally lusher environment that existed in Africa during the earlier part of the epoch.

Even so, most of the antelopes of the day were related to species that we would recognise today. For example, even at the very beginning of the epoch, around 5 million years ago, South Africa boasted a gazelle similar in size to a modern springbok. Indeed, springboks proper appeared around 3 million years ago in the same general locality, where they were represented by at least two extinct species until one of them (probably Antidorcas recki) evolved into the iconic modern animal.

The gazelles of the early Pliocene were likely different in their habits from the modern sort, being more adapted to woodland than open plains, but, moreover, they were not as common, comparatively speaking, as they are now. Instead, it appears that, at least in East Africa, a group known as the spiral-horned antelopes (about which I will have a lot to say elsewhere on this blog over the coming months) were rather more numerous.