In fact, Madagascar became an island around 91 million years ago, over 20 million years before even the likes of Tyrannosaurus appeared on the scene. Moreover, this was when it split away from what was then the island of India, with its break from Africa being almost twice as far back in time. But, even if we take that younger date for the beginning of its isolation from any sort of 'mainland', it's well before any of the sort of mammals we would recognise today had evolved. There's no equivalent here of mammoths nipping across the English Channel.
Yet Madagascar is not devoid of native mammals. Obviously, island isolation doesn't cause any problems for marine mammals that might be found off the coast, and it's not much of a problem for bats, either. But there is far more than this, animals that have somehow made the trip from elsewhere to this large and (at the time) empty land, probably by clinging to some stormswept piece of driftwood. It seems remarkable, but you've got a very, very long time to get it right, and you only need to do it once for any given group of animals.
Lemurs are probably the most famous example of this, but Madagascar also has rodents, small insectivorous mammals, and even carnivores. This last group, however, have posed a significant puzzle to biologists struggling to fit them into the wider carnivoran family tree. It's been known since the early 19th century that, due to the structure of their ear, they are all more related to the "cat" side of the order than to the "dog" one... but it's less obvious how they are related to each other, or to anything on the mainland.
The first species were formally described in the 18th century, before the concept of animal "families" had been developed. They were both placed in the genus Viverra, along with other small, bitey, vaguely cat-like animals, such as the civets I have been looking at recently. But, as more species were named, it became clear that they really appeared quite different from one another and, in some cases, from pretty much anything else.
For around 150 years, different naturalists and taxonomists came up with different schemes, placing some species in one group and others elsewhere, or just throwing up their hands and leaving the weirder ones on their own. Some were placed with the civets, some with the mongooses, and one was regularly classified as a cat, albeit one thought to have branched off from all other cats very early on.
At the heart of this, at least once evolution had become widely accepted, was just how many times new species of carnivorous mammals had reached Madagascar from elsewhere. It's something that, strictly speaking, only needs to have happened once... but that doesn't mean it did, not if their descendants are so obviously different from one another. A lack of fossils on the island, which has few deposits of the right age, didn't help matters.
In 1945, George Gaylord Simpson published an influential classification of mammals that, among many other things, answered this question: it had happened three times. The Madagascan carnivores belonged to three different groups that had, over the course of millions of years, each arrived separately on the island. Of the seven species known at the time, four were mongooses, two were palm civets, and the other one was a viverrid, but odd enough to be given its own subfamily. Aside from debates about whether mongooses were distinct enough to be given a family separate from that of the viverrids, this scheme was followed for the remainder of the century.
It was, as we now know from molecular and genetic studies, wrong.
In 2003, a genetic analysis compared the Madagascan carnivorans with each other and with similar animals elsewhere. As has been confirmed several times since, it turned out that all of the species really did share a single common ancestor that had somehow crossed over from Africa. There had only been one event, and all those features that had confused earlier researchers were down to a mix of rapid adaptation to new niches and cases of parallel evolution.
We now know that the closest relatives of these animals are, in fact, the mongooses, but the split is so far back (about 19 million years ago) that we can't reasonably place them in the same family. Not only that, but the Madagascan carnivores turn out to be more closely related to hyenas than to what had been the other prime contender, the palm civets. An old name for the group was dredged up from a 19th-century classification and raised to family level.
The Madagascan carnivores now had their own family: the Eupleridae.
Given all of this, it should not be surprising that it's impossible to describe what a "typical euplerid" looks like - there is no such thing. With every other carnivoran family, we could reel off a list of features that define them, even if there might be a few species here and there that don't quite fit the usual pattern. But, here we can't; Simpson may have been wrong about them belonging to three different groups, but it isn't as if he didn't have his reasons. That's what it looks like, with some closely resembling mongooses, some civets, and some... not.
There are, in fact, only two unique features that we can say unite the euplerids: they all descend from a single common ancestor, and they all live on Madagascar, and nowhere else. And that's it, which is unusual, especially when you can't even tell the first one is true without conducting genetic analysis.
Of course, there are some features that they have in common; they're just not unique. For instance, the structure of the bones around the ear does follow the "cat-like" pattern seen in their relatives, which at least tells us which half of the carnivoran family tree they belong to.
We can also make generalisations about their teeth; each half of each jaw has three incisors, a canine tooth, three or four premolars and one or two molar teeth. This is very similar to the pattern in mongooses, but the actual shape of the teeth varies remarkably between species, so this isn't really telling us very much beyond the fact that they are suited for a broadly carnivorous diet.
They are all forest-dwelling animals, because that wasn't really anything else to live in before the arrival of humans sometime between the third and sixth centuries AD. Since then, many of the old forests have been cut down to make way for farmland, especially in the central highlands, with the result that euplerids are no longer found through much of the interior. However, the forests that do survive are still reasonably extensive, and vary more than one might think, due to the differing weather patterns on the east and west coasts. The various species, therefore, each have their own preferences for forest type.
The euplerid family is comparatively small, with, depending on who you're asking, anything from eight to ten species. Which, to be fair, is the same as the number of living bear species and is not spread across half the globe as they are, but still. It is divided into two subfamilies, one of which itself contains unusually varied forms.
The other contains those that were long considered to be mongooses. While we now know that isn't what they really are (although, admittedly, they are closer to them than to any other non-euplerid), they are still regularly referred to as such. There has, however, been a trend in recent years to use a new word for them, taken from the native Malagasy language: "vontsira".
Next time, I will be taking a look at them.
[Photo by Rob Foster, from Wikimedia Commons.]
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