1 Life in the trees
As you work through this course you will come across boxes, like this one, which give you advice about the study skills that you will be developing as you progress through the course. To avoid breaking up the flow of the text, they will usually appear at the start or end of the sections.
As well as the course text, you will be using The Life of Mammals book (LoM) and related The Life of Mammals DVDs, as described in the introduction to this course. Before you go any further, watch 'Life in the Trees' on the DVD and read LoM Chapter 8. Unless stated otherwise, all the page references you encounter in this course will be to LoM.
The title of this course spells out exactly our focus of study; we'll be concerned with mammals that are arboreal - which means that to greater or lesser extents, they live in trees.
You won't be surprised to learn that tree-dwelling mammals don't comprise a single taxonomic group. A few familiar examples illustrate the point.
The striped possum is a marsupial. It's an agile, grub-eating tree dweller that uses its incisors to tear at wood and gnaw out wood-boring grubs. It has a sharp claw on an elongated finger, which can act as a probe or a skewer; it also has a long tongue, for probing the bark.
The binturong is the 'yard-long black hearth rug' referred to in Life of Mammals (LoM) p. 215. It's a civet - and therefore a member of the order Carnivora. It's an accomplished climber with a prehensile tail. Living mostly on fruit, it can hang upside down from branches - a lifestyle that is a significant departure from that of the more true-to-type carnivores.
You'll be familiar with squirrels as sure-footed tree dwellers - their agility is described and beautifully illustrated in LoM pp. 218-222. Squirrels are rodents - the description of squirrels as 'rats with bushy tails' has an element of biological truth.
The hyrax shows an adeptness at clambering around in trees. The middle area of each foot of the hyrax has muscles that can be retracted, so creating a suction pad that (along with rubbery soles, rich in sweat glands) help provide extra grip. Taxonomically, hyraxes belong to a group called the subungulates, which includes elephants and the aardvark.
What these examples reveal is that different evolutionary lineages have structures and lifestyles well-suited to the opportunities and demands of living in trees. In the remainder of this course, you'll come across numerous adaptations associated with tree dwelling. Many such examples - tails, claws, clinging feet - crop up again and again, revealing convergent evolution at work. Their similarity reflects the fact that the selection pressures that operate in such an environment are likely to be pretty well standard. But of course we'd expect a great deal of diversity too, in that very different types of mammals initially took to the trees. What's more, different species spend varying amounts of time in trees; some spend a good deal of time on the ground, others are on the ground fleetingly, simply to get from one tree to the other. So you'd expect tree dwellers to show varying degrees of adaptation to living in trees.
Watch the video sequence below showing climbing in the Malayan sun-bear and the tamandua - the South American anteater. (If you do not have time to watch the whole video, you should watch the section between 07:50 and 10:53 to see the Malayan sun-bear and the tamandua.) Think about the extent to which these tree dwellers are different from their terrestrial relatives. In each case, write two or three sentences that compare (a) the Malayan sun-bear with other bears and (b) the tamandua with other anteaters. Use the LoM index to find helpful information.
Distinctive features in these tree dwellers are not numerous! (a) The Malayan sun-bear has the strong forearms (and claws) of bears in general. But sun-bears are comparatively small, as you might expect of a climber. (b) The tamandua uses the powerful front legs typical of anteaters to climb, but its prehensile tail is distinctive, seemingly better suited for gripping by being more 'thinly furred' [p. 217]. But the arboreal pygmy anteater [pp. 60 and 217] also has a prehensile tail and compared to the tamandua this is more thickly furred.