Oligocene (Pt 5): The First Cats

Proailurus

As new herbivores entered Europe at the Grande Coupure, carnivores were bound to follow. As with their prey, these Asian newcomers seem to have rapidly outcompeted the native European forms, leading to a sudden turnover in the types of animals we find on the continent. Although we can say that these newcomers were "carnivorans" - the sort of mammalian carnivores we're mostly familiar with today - where exactly they place relative to the living families is harder to say.

Plesictis is an example here. It looked, so far as we can tell, rather like a polecat and was about the same size, so for much of the 20th century it was thought to be an early example of a mustelid, albeit one no more closely related to actual polecats than, say, badgers or otters are. More modern analyses are more circumspect; it may look like a mustelid in some respects, but it probably lived before those animals diverged from the raccoons and so can't be quite either. Palaeogale, which looked rather similar and was also originally assumed to be a mustelid, in fact turns out to be more related to cats and mongooses, but probably so far down the family tree that it's not yet possible to say much more than that.

Follow the Leader?

By human standards, the majority of mammal species are comparatively antisocial. Some actively avoid others of their kind outside of the mating season, but even those that are more tolerant are often found together in one place purely because that is where the food happens to be. But, of course, there are a great many exceptions to this; animals that habitually live in groups that socialise and travel together.

Animals that live like this have to have some form of decision-making process that all members of the herd, pack, or other grouping choose to abide by. The most obvious example of this would be deciding when and where to move, but it could also include, for example, determining the best way to escape predators. Lacking the sophisticated communication methods of humans, concepts of debate aren't likely to be applicable, but the decision has to be taken somehow, and, over the years, there have been many studies to determine just how egalitarian the process is and exactly which animals within the group are making the decisions if it isn't.

Attack of the Giant Hyenas

Dinocrocuta

I suspect that most non-specialists would assume that hyenas are fairly closely related to dogs. They certainly look more like dogs than they do anything else, so, absent any further information, that seems reasonable enough. But, in reality, hyenas belong to the cat-like, not the dog-like, branch of the carnivoran family tree.

This isn't some new discovery on the basis of molecular evidence, like the splitting off of the skunks from the weasel family; it's been known for a long time. This is because, when you start looking at the structural details of the skull, especially the area around the ear, everything fits with a cat-like ancestry. This much was already obvious when Miklós Kretzoi formally named the two carnivoran branches while he was working at the National Museum of Hungary during World War II. Modern evidence has merely confirmed the view, showing more precisely that the closest living relatives of the hyenas are the mongooses.

Skunks of the World: Hog-nosed Skunks

American hog-nosed skunk

There are, perhaps surprisingly, at least five different species of skunk living in the US. In fairness, two of them - the spotted skunks - are so similar to one another that it took genetic tests in the 1990s to prove they were more than subspecies, while the striped and hooded skunks are at least superficially similar as well. The fifth one is the American hog-nosed skunk (Conepatus leuconotus) and it's neither striped nor spotted.

If it's less familiar than the others, even to many Americans, that may be because it's only found in the southwest. It is common across Mexico, and also lives across Central America as far south as northern Nicaragua, but in the US it's restricted to Arizona, New Mexico, and Texas. Even here, it doesn't inhabit the whole region, being found in only certain parts of those states and avoiding, for example, both the harsher deserts and dense woodland. Although it does live in some tropical habitats at the far southern end of its range, its preference is instead for grassland and mesquite scrub, often with plenty of acacia thorn bushes. 

Hammer-Toothed Snail Eaters

As is true of mammals more generally, the majority of Australian marsupial species are herbivorous, including such familiar animals as kangaroos, wombats, koalas, and possums. (The latter, of course, are not to be confused with the American opossums, which are omnivorous and not very closely related to their Australian namesakes). Most, but not all, of those that are not belong to a single order, the dasyuromorphs, sometimes called the "carnivorous marsupials" for this reason.

Although they represent almost a third of non-American marsupial species, dasyuromorphs are far less diverse than their herbivorous counterparts, with all but one of the living species belonging to a single family, the dasyurids. Although the most famous example of the dasyurids is probably the Tasmanian devil, which eats comparatively large prey, most of the other species are small shrew-like animals feeding on insects. Alongside them, we can place the numbat and the extinct thylacine ("Tasmanian tiger" or "wolf") both of which are odd enough to be placed in families of their own.

Return of the Rabbits?

This one is wearing a radio collar...

It's abundantly clear that humans have had a dramatic effect on the number and distribution of animals across the globe. (For that matter, by some measures, plants may be doing even worse). There are great swathes of the world where particular animals were once common but are not so any more. Just to take a dramatic and obvious example, Great Britain used to be home to wolves and bears but we don't see those around any more. Those are, of course, widespread elsewhere, but other animals may be less lucky.

In some places, however, a key method in conservation may be reintroduction, bringing animals back to their native habitat, either from elsewhere, or directly from captive populations. This can help restore natural ecosystems, with the return of one originally native species helping others that are now in decline, but have yet to disappear altogether. Again taking Britain as an example, there are currently efforts underway to reintroduce beavers to the country, where they have been locally extinct since the 16th century. Similar programs for other animals exist elsewhere, but the reality is that such efforts are not always successful.

We're Up All Day to Get Lucky

One of the key characteristics that's often listed for the behaviour of a mammal species is what time of day it tends to be active. There are four basic options here, of which the most obvious are diurnality and nocturnality. The others are crepuscularity if it's most active around dawn and dusk but not in between, and cathemerality if it really doesn't care - often because it lives underground. But, either way, it's natural to assume that this behaviour is relatively fixed in an animal; either it's nocturnal or it isn't.

In reality, however, it turns out that this can have a lot to do with the circumstances. And, in the modern world, those circumstances are most likely to be shaped by... what else, but humans? 

The issue, of course, is that humans are for the most part diurnal. Which isn't much of a problem for animals that are naturally nocturnal, but can be if they, too, would prefer to be active during the daylight hours. What we see time and time again across the world, and across different mammal species, is that where humans are most likely to encounter wild animals, those animals shift their behaviour towards nocturnality to avoid the stress of meeting us too often.