Twilight of the Almost-Primates

The primates are one of the major groups within placental mammals, currently considered to contain at least fourteen different living 'families', and probably more. Given this, and the fact that they are fairly distinctive, it's not surprising to discover that they are also a very ancient group. Genetic studies, back by estimates of how frequently mutations ought to occur, imply that they may date all the way back to the extinction of the dinosaurs, or at least its immediate aftermath.

The oldest undisputed fossil primate we currently know of isn't quite that old, however, and dates back 'only' 55 million years to the dawn of the Eocene epoch. I have to add the word 'undisputed' to that, though, because it wasn't alone - a number of other very primate-like animals did live at the same time, and, indeed, somewhat earlier.

These animals are collectively called 'plesiadapiforms', and it would be fair to say that there is still some considerable debate as to what they actually were. Just as with the question as to how many families of living primate there are, this depends not on how the different groups are related, but on where we choose to draw the lines between them. In the case of living families, the question is whether we consider marmosets and night monkeys to belong to the broader capuchin family, or whether we consider them different enough to count as families in their own right. In the case of the plesiadapiforms, it's whether they're really weird early primates, or whether we consider them to be merely close relatives.

How Baby Bats Learn to Fly

Small mammals, on the whole, live fast and die young; a great many of them live for only a single year. And that's assuming they don't get eaten first, which, unsurprisingly, they often are. In order to maintain their numbers, then, it is essential that they breed early and often. In particular, they tend to have large litters, which they then need to get to adult independence as quickly as possible. The common house mouse, for example, can breed at least five times a year, and gives births to litters of typically around five to eight pups at a time, each of which is sexually mature within less than two months.

This is not, however, what we see with bats.

The Grunting of Baboons

Olive baboon

While they also often have other means at their disposal, mammal species typically communicate with one another through sound. For those that live solitary lives, this tends to be fairly unsophisticated, beyond, perhaps, the need to attract and woo a mate. For social animals, sound production can, however, be more complicated, allowing the sort of short-term immediate communication for which scent-marking is not appropriate.

An obvious example are alarm calls, in which one member of a herd or other group will alert its fellows of a predator or other threat. Another are the distressed 'separation calls' that young mammals use when they can' find their mother. And then, of course, there are mating calls, or aggressive roars and the like intended to intimidate a rival.

But there are also peaceful, non-sexual, contact calls whose primary intent appears to be simply maintaining the cohesion of the group. For example, meerkats regularly use calls to decide when to move on to new foraging grounds, keeping the group together using the principle that if three or more members 'vote' to move by making the appropriate call, then everybody moves at once. African elephants can even use long-distance communication to maintain social bonds with individuals that may be literally miles away.

The Pig Family: Fossil Pigs

Kubanochoerus, the unicorn-pig

There are seventeen widely accepted species of pig alive today. Although some, notably the wild boar and the two kinds of warthog, are doing absolutely fine in the grand scheme of things, many are threatened to varying extents by hunting and loss of habitat. Three - the pygmy hog and the Visayan and Javan warty pigs - are formally listed as endangered species by the IUCN, and many of the others are just outside that category. On the bright side, no clearly identified species of pig has actually slipped over the line into extinction in the last few thousand years. But, of course, if you go back a few million years, it's a rather different story.

Indeed, in some respects, the pig family as it exists today is a shadow of its former self. Pigs have always been reasonably successful animals (at least, without human interference), given their adaptability, moderate intelligence, and willingness to eat just about anything. But, in the past, they were more varied than today. In total, there are five generally recognised subfamilies within the overarching pig family - and all but one of them are known only from fossils.

Miocene (Pt 10): The Beasts with Three Horns

Syndyoceras

At the dawn of the Miocene, 23 million years ago, North America was, in many respects, quite different from the way it is today. It was, at the time, separated from South America by a wide expanse of sea, and, perhaps more significantly, the Sierra Nevada and Cascade Mountain ranges, which today run from southern British Columbia down into Mexico, did not yet exist as any more than a series of particularly high hills. While the Rockies were already mountainous, so that there was at least some rain shadow, in general, the continent was wetter and more forested than today, lacking the great grassy prairies that are so dominant today.

As the climate warmed, sea levels rose, flooding low-lying coastal regions and turning major valleys into bays. For much of the epoch, for instance, Florida was almost entirely underwater. Further north, however, it was still connected to Asia (and Greenland, although that's less significant in the grand scheme of things). Perhaps because the land bridge was both far to the north and relatively mountainous, not many animals seem to have crossed it, but that changed in the Early Miocene as the climate began to improve, and only increased as the epoch wore on. And, for whatever reason, most of them were heading east - into America.

The Best Time for Breeding

Animals, as a rule, want to give birth when their offspring have the best chance of survival. In particular, it's useful to give birth at a time when suitable food is most abundant, whether it's to allow the mother to produce enough milk, or to wean the growing young onto solids more quickly. If the animal in question is short-lived, the time of year may not matter too much, so long as the mother is well-fed and in good physical condition. If you have to breed multiple times each year, you'd better get on with it.

It may also not matter too much if the animal lives somewhere where the seasons don't change too much, although, even in the tropics, where there's no winter, there's usually a rainy and a dry season. A great many mammals, however, do have a specific breeding season, timed to be one gestation-length away from the best time to give birth. If pregnancy lasts six months, and the best time to give birth is in the spring, when fresh plants are sprouting, you'd better do your mating in the autumn. If pregnancy lasts twelve months, however, you want to mate in the spring. And so on.

Bats That Eat Fish

Greater bulldog bat

With over 1,300 different species of bat known, it shouldn't really be surprising that there's a wide range of different dietary habits among them. Of course, a lot of that is on a fine scale, as I discussed just last month, but there are more significant differences in the kinds of things that bats feed upon. Insects, fruit, nectar, even blood all form the core diet of at least some kinds of bat.

One of the more unlikey food sources, however, is fish. Yet, when you think about it, fish is a really common food source for birds - there are a huge number of bird species that feed primarily on fish, including seagulls, kingfishers, and ospreys, among many others. Clearly, there's no inherent reason why a flying mammal couldn't eat fish, yet very few of them do.

As a recent review makes clear, however, "very few" is not "none".