Sunday, 1 March 2015

Dog-toothed Beasts from the Time Before Dinosaurs

What sort of animals did mammals evolve from? For birds, the answer is simple: they evolved from reptiles, and specifically, from dinosaurs. (Which is why we say, using the modern definitions of things, that birds are dinosaurs). With mammals, though, the situation isn't quite the same.

The first mammals appeared around 225 million years ago, not long after the first dinosaurs did. However, they were not descended from reptiles, but from an entirely separate evolutionary line - the Synapsida - that had lived alongside the reptiles for a very long time. Yes, if you go back far enough, reptiles and mammals do have a common ancestor, and that animal would have looked, to modern eyes, more like a reptile than it does a mammal. But it wasn't a reptile, not in the modern scientific sense, and it belonged to a group of animals that just aren't around any more.

But between the point when that animal lived, and the first mammals appeared, there were a whole host of other, non-mammalian, synapsids. We often divide these creatures into two broad "grades" of evolution: the early, reptile-like, pelycosaurs, and the later, more mammal-like, therapsids. (In fact, of course, the two lived together for quite some time - it's not that one simply turned into the other. Evolution is more complicated than that). A greatly simplified tree of the "true" therapsids is included below, and shows that early mammals had rather a lot of relatives.

Sunday, 22 February 2015

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.

Sunday, 15 February 2015

Infidelity Among the Aardwolves?

This year's Synapsida survey of the species in a family of mammals is, of course, that of the dog family. I've already covered wolves and coyotes, jackals will be up next, and then, alongside a few others, you're going to see an awful lot of foxes. What you won't see any of are hyenas.

That's because hyenas, physical appearance notwithstanding, are not dogs. In fact, they're actually more closely related to cats than they are to dogs. (Although they're closer to mongooses than to either, for what it's worth). One of these days I may get round to a description of the hyena family, and how it's different to that of the dogs, but that won't be a terribly long series of posts, because there are only four living species.

There's the one everybody knows, which is the spotted or "laughing" hyena, and there's a couple of smaller, rarer hyenas related to it. And then, there's the aardwolf (Proteles cristata). Aardwolves are, to be honest, pretty strange animals, and there's a lot to be said about them, their feeding habits, and so on. This, however, is not that post. Because, yesterday being Valentine's Day and all, it's time to talk about mating behaviour.

Sunday, 8 February 2015

The Dog Family: Coyotes and Red Wolves

Grey wolves are found across the Northern Hemisphere, but they originated in Asia, only reaching the Americas via the Bering land bridge when sea levels were low. Most of their close relatives are also found in the Old World, but there are one or two very closely related species in North America. Of these, by far the more common and better known is the coyote (Canis latrans).

Coyotes first evolved, in North America, during, or shortly before, the Ice Ages, almost certainly from the now-extinct Pliocene species Canis lepophagus. Today, they are found throughout almost the whole of North America, from Alaska to Panama, being absent only from eastern Canada, the Caribbean coast of Central America, and a number of islands. In this respect, they have actually benefited from the presence of humans; before the arrival of Europeans, coyotes did not live anywhere along the east coast of America, and only moved in once we started chopping trees down to make way for cities and farmland.

Saturday, 31 January 2015

Pliocene (Pt 3): Of Gazelles and Three-toed Horses

The Zanclean Flood may have been a catastrophe of epic proportions, but, so long as you were above where the flood waters eventually stopped, Europe at the dawn of the Pliocene was a fairly pleasant place. The weather was warmer than today, and, apparently wetter too, which might not be what time-travelling tourists would be looking for, but was certainly good news for the plants that were actually there. Where places like Spain, Italy, and Greece are today dominated by... well... "Mediterranean" scrubland, back then they would have been considerably greener. And what's good for plants is good for herbivores.

Especially when it comes to cloven-hoofed animals, many of these would have been animals that would have been, at least in general terms, familiar to us. Not necessarily familiar to us from Europe, though, since, in addition to pigs, bovines, and deer, there were also a number of antelopes. These were mostly members of the gazelle subfamily, although there were others, including some, for example, related to the modern sable antelope. The gazelles included Hispanodorcas, a small and slender antelope with slightly twisting horns, with fossils found in southern Spain. However, some were even closer to the gazelles of today, to the point that, if, like most people, you'd be pressed to tell the difference between a Dorcas gazelle and a Speke's gazelle today (or at least, to know which one was which), you'd probably not have identified these as anything different, either - although at least some of them were smaller than any living species, which might have helped.

Sunday, 25 January 2015

What is a Primate?

Brown lemur
In 2012 and 2013, I finished off the year by posting short(ish) responses to questions entered into search engines that had, according to the blogger interface, led people to Synapsida. I didn't do this last year, because the great majority of the questions were ones I had already answered - perhaps an artefact of how many posts there are now at this blog. But somebody did ask "what is the definition of a primate?" and that struck me as something I could expand on at length. So here we are. What is a primate?

The simple, dictionary, definition is "a member of the order Primates". That's obviously a circular, and rather unhelpful, definition, but, then dictionaries aren't the same thing as encyclopaedias. But even it requires picking apart a bit. For a start, note the capital 'P' in the word "Primates". This indicates it's the name of a discrete thing, and not just the plural of the word "primate". It's a Latinate word, like "Rodentia" for the order of rodents or "Proboscidea" for the order of elephants and their extinct kin. Which means that it may not be pronounced the way you think; it has three syllables: Prime-ATE-eez. It literally means "of the first rank", because, you know, anything with us in it has to be of the highest rank. (Hence the title "primate" given to some high-ranking bishops).

Sunday, 18 January 2015

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?