Sunday, 23 November 2014

Pliocene (Pt 2): Survivors of the Zanclean Flood

For verily, I shall inherit the continent!
As I noted last time, officially, the dawn of the Pliocene - the autumnal epoch immediately prior to the Ice Ages of the Pleistocene - is marked by one of many changes in Earth's magnetic polarity. However, that particular event wasn't picked at random; there really were visible changes at the time. And, in Europe, none were more significant than the Zanclean Flood.

To understand what this is, though, we have to turn to the latter part of the preceding epoch, the Miocene, and take a look at the Messinian Salinity Crisis. The Miocene was much longer than the two epochs that followed, long enough that, over the course of it, the continents moved about a fair bit. Towards the end of the epoch, then, moving northwards, Africa hit Europe.

Due to the shape of the respective continents, however, this didn't result in the sort of massive mountain building that we see in present day Tibet (or, at least, it hasn't yet - the continents are still moving). But it did have a dramatic effect nonetheless. Crucially, the continents didn't just nudge up against one another in the east, creating what is now the Sinai, but also in the west, creating a land bridge between modern Spain and Morocco.

The Mediterranean Sea became land-locked. The Mediterranean climate of the day was even hotter and drier than it is now, and, free from any connection to the Atlantic and Indian Oceans, the sea began to evaporate. Over the course of hundreds of thousands of years, the sea level dropped. Not just a little bit, but by as much as three miles.

Sunday, 16 November 2014

Growl Whistle Squeak

While scent marking, for example, is great for leaving long-lasting messages, for other purposes, vocal communication has a number of advantages. However, since non-human animals can't talk, this necessarily imparts less information than it does in our own species. But how much less? Or, to put it another way, how complex can animal vocalisations get?

The number of different sounds an animal can make depends on a number of factors. Many of these are physical, due to the way that their larynx and vocal cords are set up, and to their ability to modulate the sounds it produces with their mouth, lips, and so on. For instance, while there has been at least some success in getting chimps and gorillas to use human sign language, they can't actually speak because of purely physical limitations in their upper respiratory tract. Added to this is the matter of just how much complexity they need to get across anyway.

Broadly speaking, the more sociable an animal is, the more need it has for complex communication. If you rarely come across other members of your own species, you probably don't need to say much when you do. A simple "go away" is probably about as much as you need, and you can co-opt the same threat against hostile members of other species, too. Beyond that, you may need some kind of mating call, and a means for mothers to find their offspring, and you're pretty well sorted.

Sunday, 9 November 2014

Figs and Pepper: the Diet of Fruit Bats

Carollia brevicauda, the silky short-tailed bat
The majority of bat species eat insects, often caught on the wing, using their remarkable sonar abilities. But there are a vast number of bat species, and by no means all of them have this diet. Probably the best known exceptions are the fruit bats and the vampire bats, of which the former are far more numerous.

In fact, fruit-eating has evolved at least twice among bats, both times in the tropics, but on opposite sides of the globe. As a result, there are two, quite different, kinds of fruit bat in the world. In the Old World - Africa, Asia, and Australasia - we have the flying foxes, the exceptionally large bats with long, almost dog-like faces. Indeed, these look so different from other bats that they were long thought to represent an entirely separate lineage within the bat family tree, although the truth turns out to be more complex. When the term "fruit bat" is used without qualification, it's more likely to refer to these, and they've been somewhat in the news lately as the likely origin of the Ebola virus before it spread to humans.

The other group are found in South and Central America, and look much more like typical bats. This group includes the tailless fruit bats (Artibeus spp.), the short-tailed bats (Carollia spp.) and the yellow-shouldered bats (Sturnira spp.). One of the problems with talking about bats is that, especially with species outside of Europe and North America, they don't have common English names. Well, technically, most of them do, names made up by scientists because they feel they probably ought to, but nobody outside of a specialist knows what they mean, and they tend to be rather cumbersome. So, for once, I'm going to stick to those scientific names in what follows.

Sunday, 2 November 2014

Mini-Monkeys: The Odd One Out

Goeldi's monkey
Under the scheme that I have been using over the last year, there are 42 currently recognised species in the marmoset family. Of these, 22 are marmosets, and 19 are either tamarins or lion tamarins. It doesn't require much arithmetic to deduce that there must therefore be one member of the family that's neither.

This is Goeldi's monkey (Callimico goeldii). It is sometimes called "Goeldi's marmoset", or, less commonly, "Goeldi's tamarin", but these names are misleading and inaccurate. It is, undoubtedly, a member of the marmoset family, but it's equally clear that it is quite different from anything else within that family.

First, the similarities. Goeldi's is about the same size, at about 25 cm (10 inches) in body length, as other members of the family, and therefore much smaller than any monkeys outside the family. It has similarly luxuriant fur, in its case almost entirely black, with an almost mane-like ruff around the head. Like members of the marmoset family, but unlike other monkeys, it has claws, rather than nails - something it uses to cling on to rough bark. It also lives in roughly the same area, in the high altitude western margin of the Amazon, from Colombia down to Bolivia and in to western Brazil.

Sunday, 26 October 2014

Children of the Coal-beasts

The animals of the Pleistocene epoch, of which I've given an overview over the last couple of years, are, on the whole, readily recognisable; they may look different from those today, but it's pretty obvious which modern animals they're related to. Mammoths are clearly elephants, sabretooths are clearly cats, and so on. The further we push back into the Age of Mammals, however, the less clear such things become.

There are two main problems here. One is that the animals simply look less like the ones we have today, especially if they come from a time before the modern groups separated from one another. How do we tell which modern group (if any) an animal belongs to if it lived before that group developed the characteristics that define it today? Secondly, older fossils are both rarer and more fragmentary, so that we're literally missing pieces of the puzzle. As a result, there are a number of early groups of mammal that we know existed, but which it's hard to fit into a family tree, or, indeed, to know much about at all.

Sunday, 19 October 2014

How Elephants Bring the Rains

The largest species of land-dwelling animal alive today is, of course, the African bush elephant (Loxodonta africana). Especially since they're herbivores, and much of their food, such as grass, isn't terribly nutritious, they need to eat an awful lot of it to survive. Certainly not all their food is low quality, and, in fact, they'll eat just about any vegetation they can find, and they do have a digestive system that extracts more nutrition from low-calorie forage than a human one could, but even so, a full grown male has been estimated to eat about 150 kg (330 lbs) of food each day

Which isn't so bad, if you happen to live in a densely vegetated environment. The rather smaller African forest elephant (Loxodonta cyclotis) does just this, inhabiting jungles north of the Congo, but was only recognised as being a separate species in 2010. The bush elephant, while it, too, often lives in dense forest, also seems happy to inhabit less favourable habitats. For example, a significant number live in the savannah of the Serengeti in East Africa, and in similar environments. At the extreme, some live on the edges of deserts in places like Mali and Namibia.

Sunday, 12 October 2014

The Mysterious Songs of the Blue Whale

The blue whale (Balaenoptera musculus) is, as is fairly known, not only the largest animal alive today, but the largest that has ever lived. Far larger, for instance, than anything that lived during the time of the dinosaurs. Yet, because, like all whales, they are not that easy to study, they remain relatively mysterious, compared with large land-based mammals.

There, however, are a number of different ways in which we can study them, and one of them is to listen to their calls. Like other whales, blue whales produce 'songs' that travel for miles through the deep, and, by listening to them, we can get at least some idea of where they are, and how numerous they are, and perhaps further information besides.

Compared with cetaceans like the humpback whale, the songs of blue whale are not particularly complex - although they remain more so than deep clicking sounds of sperm whales. For the most part, blue whale songs consist of the same element repeated over and over. This element, termed a "Z-call" because of the shape it produces on a spectrograph, has three parts: a long, deep rumble, followed by a rapid dip and then a short, musical tone at an even deeper pitch. The first part is commonly somewhere about the A four below middle-C, which is the very lowest note than can be produced on a grand piano. The last part is about three or four notes lower than that, which is generally considered below the range of normal human hearing.