Oligocene (Pt 11): Early Monkeys and Two-Ton Herbivores

Arsinoitherium

Because the Oligocene is so much further back in time than the later epochs, especially the Pliocene and Pleistocene, there are more gaps in our knowledge of it. That it's also much shorter than the epochs to either side of it means that those gaps can, proportionately speaking, occupy far more of its length. One of the places where such a gap is particularly noticeable is the history of primates.

Monkeys first appeared in Africa in the latter half of the preceding epoch, but their early record is patchy. This is likely because many of the earliest monkeys lived in areas that simply weren't conducive to forming fossils - although the fact that many parts of Africa have not had the same detailed paleontological surveys that other continents have may also be a factor. Much of the history of the primates during the epoch is a blank... but not entirely.

700th Synapsida

Well, here we are again with another biennial look-back at the last 100 posts, highlighting what may have been missed and taking a brief peek at where I might go next. I can't say it's entirely gone without a hitch over the last couple of years, but I've mostly kept to the weekly schedule... although you might get more regular gaps in the summer going forward.

Evolution remained the single most common category for the past 100 posts, which is hardly surprising given how many are about extinct species, and how important it can be to understanding how the living ones got to be the way they are. However, diet and habitat, which are often linked, have overtaken animal behaviour to nab the second and third spots... although the latter has remained common. Since I pick most topics on the day, without any grand plan to even things out, that's probably just the vagaries of what I happen to have come across. 

Hair, Fur, Bristles, and Spines

Trinomys

Hair is one of the key defining features of mammals. Apart from cetaceans, such as dolphins, no mammals are entirely hairless, although, for example, hippos and some babirusa species come very close. The original purpose of hair was almost certainly to maintain body heat, something that matters to warm-blooded animals in a way that it doesn't to, say, reptiles. Since then, however, hair has adapted to fulfil many other functions as well.

To begin with, there is colouration, a function that hair needs to take over once it obscures the skin. The most obvious way that hair colour can help an animal is camouflage. While this is instinctively true, there have been statistical studies that demonstrate certain hair colours are, indeed, more common in animals living in certain environments. For instance, multi-species analyses of lagomorphs and cloven-footed mammals have shown that animals with grey fur are more likely to live in rocky environments. The same studies, as well as similar ones on carnivores, show that pale fur is associated with open environments, especially deserts, while dark fur is most common in those animals living in jungles, dense forests, or heavily vegetated swamps. And, surely to the surprise of almost nobody, white fur is associated with the Arctic, or with the winter coats of those living where it snows.

Antilopine Antelopes: Dwarf Antelopes of southern Africa

Steenbok

The "antilopine" subfamily of antelopes, so named because it happens to include the first animal scientifically described as an antelope rather than a goat, is itself divided into at least two major branches. There may or may not also be minor ones, depending on what you think is worthy of naming, but the two main ones are quite clear, and perhaps separated from one another around 12 million years ago towards the end of the Middle Miocene.

One of these groups contains the gazelles, along with the springbok, some other gazelle-like animals, and that "first" antelope mentioned above, the blackbuck. These are, for the most part, smallish slender, fast-running antelopes living in arid or semi-arid habitats in both Africa and Asia. The second group are the dwarf antelopes, found only in Africa and quite visibly different from gazelles. 

Unravelling the History of Seals

Allodesmus, a desmatophocid

Trying to determine the largest patterns in evolution can be a daunting task. Here, we often want to look at large numbers of species, comparing the living ones and filling in the gaps with fossils that are often incomplete, ambiguous, or that simply haven't been discovered yet. As a result, there are several big transitions in mammalian evolutionary history that we'd like to get a better look at. Bats are a significant case in point; their small fragile skeletons don't preserve well if we want to see more than teeth, and how they developed their forelimbs into wings remains obscure.

With some groups, however, we do have sufficient fossil evidence that we can look at a whole group of animals and get some idea, not just of how it originated, or where it fits in the larger mammalian family tree, but what ups and downs it has faced over the course of its existence. This can tell us what alterations in climate or geography drove changes within the group and how and when particularly evolutionary innovations developed.