|This is a synapsid, and not a reptile. Yes, really.|
It's not going to help the people who asked the questions in the first place, of course. And, if anyone asks the question again, there's no guarantee they'll be directed to this page, rather than wherever they were directed before. But what the heck - why not, right?
So without more ado:
Is [X] a Synapsid?
This seems to be among the top two or three questions that bring people to the site. Is a cow a synapsid? Is a tiger a synapsid? What about a monkey? Or a kangaroo? And so on.
The short answer is "yes".
At least, it is if you're asking about a mammal - if anyone's ever asked if a crocodile is a synapsid (it isn't) I've not seen it. Basically, all mammals are synapsids. And, yes, for the avoidance of doubt, marsupials, such as koalas, kangaroos, opossums, and so on, are mammals, and therefore also synapsids. So, for that matter, are platypuses and echidnas. If the mother gives milk to its young - no matter how it produces those young - it's a mammal. And, if it's a mammal, it's a synapsid.
For that matter, all living synapsids are mammals. So, if it's alive today, and isn't a mammal, it's not a synapsid, either. So no reptiles, birds, or whatever. Way, way, way back in time, when dinosaurs were, at best, a pretty new thing, there were synapsids that weren't mammals. But they're all gone now, and have been for a very long time indeed.
So what is a "synapsid" anyway? I've answered this a couple of times before, but there's nothing to stop me repeating myself. In short, the Synapsida is the evolutionary line that leads to, and includes, the mammals. It's defined by the shape of the skull, and is distinct from the Diapsida, to which birds, and many (perhaps all) living reptiles, belong. There's some debate as to how far the Diapsida extends - it may, or may not, include turtles and tortoises. Either way, it's beyond the scope of this blog, so we'll leave the herpetologists to fight that one out among themselves.
The reason that mammals are synapsids is that, in modern classification schemes, all officially named groups of animals must be complete. That is, they must consist of a single common ancestor and all of its descendants - no ignoring something you don't like the look of. If an animal evolved from a member of a particular group, it itself is also a member of that group. Mammals evolved from synapsids, therefore mammals are synapsids.
Mammals, on the other hand, are not reptiles. That's because the last common ancestor of all reptiles that are alive today wasn't, as it happens, also an ancestor of mammals. That allows us do a neat trick where we say that early synapsids (which certainly looked reptilian) were not, in fact, real reptiles, but something else.
Birds, on the other hand, descended from dinosaurs, which most certainly were reptiles. That is, they were descended, if you go back far enough, from the same extinct animals as today's lizards, snakes, and crocodiles are. This means that, strictly speaking, birds are reptiles. Or reptiles don't exist. Take your pick.
But mammals are mammals, and do exist. So I'm okay.
What Animals Have Four Stomachs?
It's pretty obvious why this question turns up a lot. That post explains, in some detail, why cows, and other ruminants, have a four-chambered stomach, and why horses (for example) don't. It touches on the question above, but here's a more direct answer:
Cattle, sheep, goats, antelopes, deer, giraffes, okapi, and chevrotains.
That's well over a hundred species, most of them either antelopes or deer. Consider, for example, that when I say "cattle", I'm including not just the domestic sort, but related species such as bison, buffaloes, and yaks. And "antelope" is a really broad term that includes gazelles, impalas, and whatnot. (And, yeah, if you want to be pedantic, I'm including pronghorns as antelopes, and musk deer as deer, which, technically, they aren't.) This means that, say, pigs, peccaries, and hippos just have a single-chambered stomach, as do some other large herbivores, such as horses, tapirs, rhinos, and kangaroos.
It's not, however, a complete list because:
Whales, dolphins, and porpoises
...also have a four-chambered stomach, even though they aren't ruminants. It's weird, but there you are. While we're at it:
Camels, llamas, guanaco, vicunas, and alpaca
...have a three-chambered stomach. Just to be different.
Are Rabbits Rodents?
No, they aren't.
Neither are hares or pikas, although the latter, in particular, do look quite like rodents. Perhaps slightly more obviously, things like shrews, hedgehogs, and moles aren't rodents either. Essentially, all of these animals have too many teeth to count as rodents, and, in many cases, the teeth aren't even the right shape.
There are, on the other hand, an utterly huge number of species that are rodents. Mice, rats, squirrels, chipmunks, beavers, marmots, porcupines, guinea pigs, hamsters, gerbils, gophers... and those are just some of the better known ones. There's thousands of the little buggers. Seriously.
Incidentally, a variant of this question I've seen more than once is "are rabbits rodents or mammals?" Which seems a bit odd, because rodents are also mammals, so it isn't an either/or question. Mice, for example, are both rodents and mammals, at the same time. But, yeah, rabbits are mammals, but they aren't rodents, if that's what you were wondering.
Again unsurprisingly, I've seen a number of these. Here's a selection:
How are ferrets and polecats linked?Ferrets are basically domesticated polecats. There is also a wild species, the black-footed ferret, that should perhaps more accurately, be called polecats. Note also that, in America, the term "polecat" is sometimes used for skunks, which are quite a different kind of animal, and not very closely linked at all.
What's the difference between mink and ferrets?Mink are more aquatic than ferrets/polecats, but the two kinds of animal are very closely related. You can get the skinny here and here.
What's the biggest weasel?It depends what you mean by "weasel". The largest living member of the weasel family is, in fact, the giant otter. If you don't consider otters to be weasels, the largest close relative of the common weasel is probably the steppe polecat, although some of the other polecats, and indeed, the American mink, are pretty similar in size. If you really insist that the animal actually be called a "weasel", then I'd say it's the Malaysian weasel, which is about ferret-sized.
Did cats evolve from weasels?This is an interesting one. To cut to the chase, the answer is "no". Cats and weasels are separate families of animals, and, aside from being carnivorans, they aren't even that closely related. At quite an early stage, the carnivorans divided into two evolutionary lines: cat-like carnivores, and dog-like carnivores. Weasels, as it turns out, are "dog-like" - the difference is in the structure of the ear - but, even so, dogs didn't actually evolve from weasels, either; they're just related. On the other hand, many early carnivorans, being small and meat-eating, did look a bit like weasels, so it's not an unreasonable question. But, for what it's worth, the animals that cats did actually evolve from probably looked more like tree-climbing meerkats than anything else.
Do animals other than humans have anal sex?
I have no idea how this question got someone to my blog, but apparently it did! So, you know, what the heck: yes they do. Bonobos, which are amongst our closest relatives, are probably the most famous for it. Come to that, bonobos really take the idea of "make love not war" to extremes, and they will happily engage in oral sex, lesbian sex... you name it. But bonobos aren't alone, and it's actually pretty common in the animal kingdom. So here's a picture of two lions going at it. You're welcome.
Synapsida will return in the New Year.
[Picture by Bogdanov, from Wikimedia Commons]