The Crusty Forearms of Male Bats

Bats, of course, are not blind. There eyesight is, in fact, pretty good in the majority of species. Which makes sense for an animal that has to fly around at night when the light is dim but not entirely absent. It's only for animals like moles, which live underground, where the light can't penetrate at all, that vision becomes an expensive and unnecessary luxury.

Having said that, many species of bat do spend a lot of time in caves, and, in there it really is too dark to see anything, no matter how good your night vision might be. As a result, the other senses of bats are often highly tuned. Hearing is the obvious one, since bats rely on that for their sonar abilities, but many species also have well-developed senses of smell. In particular, since bats also tend to be highly social, scent often forms a crucial part of their ability to communicate with one another - as it does for many other mammal species.

Dive of the Fossil Penguins

This is the post that will be current as of 1st April 2016. I will therefore be following my long-running annual tradition (that's "long-running" as in, "I've kept up this annual tradition for a whole year now") of posting about something that isn't a mammal, or even a synapsid.

When we think of 'birds' the ability to fly is surely one of the first things that come to mind. Indeed, the development of flight was surely one of - if not the - defining moments in early bird evolution. But, whereas bats have never given up that particular evolutionary innovation, flightless birds have evolved more than once. And, because we know that the very first birds could already fly, it follows that all flightless birds have ancestors that were perfectly capable of flight, but, for whatever reason, lost the ability.

Many, such as ostriches, did so to develop a fully land-based lifestyle, often becoming much larger in the process. But others swapped flight for diving ability. Of course, there are a great many diving birds that are still able to fly, but sometimes there is an advantage in really specialising in diving to the point that flight is no longer an option. This has, in fact, happened more than once in the course of avian evolution, but the only flightless diving birds we have now are the penguins, propelling themselves through the water with wings shaped like flippers.

Eau de Raccoon

Most mammals have a better sense of smell than we do. They are able to use this in a range of different ways that suit whatever their particular needs are, such as identifying food, avoiding predators, and so on. But another key use, one that's essentially lost in humans, is as a means of communication. For the most part, this means scent marking, that practice, so familiar to dog owners, of leaving signals around for other members of your species to identify.

There are basically three ways that mammals leave scent marks. There's urinating, leaving dung around, and using glands specifically evolved to create smelly secretions. Having abandoned scent marking, we humans lack proper scent glands, and the closest we get are some modified sweat glands in the armpits and groin that create a special kind of sweat that smells, instead of the usual odourless watery stuff that the rest of our skin makes. And, really, compared with proper scent glands, that's pretty pathetic.

The Smell of Success

One of the noticeable features of mammals, when compared to other vertebrates, is that they tend to have a highly developed sense of smell. Most vertebrates can smell, even if, in the case of fish, it's not quite what we'd think of by that term. Indeed, the sense of smell is pretty poor in most fish (sharks are among the exceptions, hence that blood-in-the-water thing), and it's also rubbish in birds, and not too great in many amphibians. It's rather better in reptiles, but the snakes, which appear at first glance to be really good at it, actually do so by cheating (more on that later).

But, by and large, the sense of smell reaches its apogee with the mammals. It's not just dogs that have a far better sense of smell than you do. It's also mice, deer, cats, and many others besides. The mammalian olfactory system is superbly evolved, and this dates right back to the origin of the class. In short, it's usually far better than anything we've got.

Except... um... we are mammals. So what gives? Why are we humans so useless at something that our fellow milk-giving relatives have perfected? Something that, presumably, has a lot to do with the success of mammals as a class?