Saturday, 29 November 2014

The Dog Family: Canidae

A wolf
The dog family does not have the same variety of different forms and species as does the weasel family. I also suspect that, with the exception of grey wolves, it doesn't get the sort of attention that the big cats do. Yet, of course, even apart from the wolves and their domestic descendants, it includes a number of familiar species, as well as some that are rather more exotic. So, with goats and marmosets out of the way, let's turn to the taxonomic family of man's best friend.

With, perhaps, one or two exceptions, most members of the dog family are instantly recognisable as such. Ignoring the domestic breeds, they typically have muscular bodies, long legs, large, mobile, ears, heads that are broadly triangular in shape, and bushy tails.

Their legs are the shape they are because they're adapted to chasing prey, and most dogs are therefore pretty good at running. They have four toes on each of the hind feet, and, while most of them do have the full set of five on the front feet, the thumb (or "dewclaw") doesn't reach the ground. Their snout is the length and shape it is, partly to get in a large and sensitive nose, and partly to fit in an array of teeth that don't restrict them purely to eating meat.

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.