The Social Lives of Ground Squirrels

There are almost 300 recognised living species of squirrel. As one might expect given that large number, there is a fair degree of variety among them. To people living in Britain, for example, the word "squirrel" typically conjures up a small, tree-dwelling animal with a bushy tail. We only have two local species (one of them invasive) and they're very closely related. Take a look further out in the squirrel family tree, however, and we see some significant variations on the general theme of "squirrel-ness".

Perhaps the most obvious of these are the ground squirrels. Most ground-dwelling squirrels belong to a single evolutionary group, which includes something like a quarter of all known squirrel species. Many of these - the animals most commonly known simply as "ground squirrels" - look much like their tree-dwelling kin, but the group also includes such animals as prairie dogs and marmots as well as the semi-arboreal chipmunks.

Small Cats: Servals in the Savannah, Cats in the Congo

Serval

The best-known wild cats living in Africa are, of course, the large ones: lions, leopards, and cheetahs. South of the Sahara, they are joined by two species of small cat: the African wildcat (from which the domestic animal is descended) and the black-footed cat, both of which I have already described in this series. To these, we can add the caracal, a medium-sized cat that closely resembles the lynxes of Eurasia and North America. But, although this was most likely the animal that the word 'lynx' was originally coined to describe, the caracal is not closely related to what we would now regard as the 'true' lynxes. Instead, it is part of a distinctively African lineage of similarly medium-sized cats, containing just two other living species.

The more familiar of the two is surely the serval (Leptailurus serval), an animal that is not only widespread across Africa, but that happens to be relatively easy to breed in zoos. The name apparently derives from an alternative (and now obsolete) Portuguese name for the lynx that has now replaced variants of the older English name of "tiger cat" in most non-African languages. (It's still tierboskat - literally "tiger-forest-cat" - in Afrikaans, and, unsurprisingly, languages such as Swahili had perfectly good words for it already).

Miocene (Pt 22): Last of the Creodonts

The largest predator in Africa today

The dominant mammalian carnivores in Africa today are the lions, hyenas, and leopards, with cheetahs and wild dogs also playing their role. The ancestors of all of these creatures first reached the continent from the north, shortly after it collided with Eurasia during the Early Miocene. For the most part, at the time, their ancestors were small, with hyenas, for example, being no larger than mongooses. But this does not mean that Early  Miocene Africa had no large predators at all.

For one thing, the cats, hyenas, and so forth, were not the only carnivorous mammals to have made the crossing from Asia. The animals known as bear-dogs, or more technically, amphicyonids, are far better known from Europe, Asia, and North America, but they did reach Africa, too. 

Like a Hole in the Head: What's the Point of Sinuses?

We're probably all generally familiar with the existence of what are technically termed paranasal sinuses. That's largely because the inflammation of them, known as sinusitis, affects as many as 1 in 8 Americans, and presumably a similar number of people elsewhere, at least in the west. The term 'sinus' just means an empty space in something, and in the case of the paranasal sort, those spaces are inside the bones of our skull, connected by narrow passages to the nasal cavities.

The existence of these passages is important, ensuring that the sinuses are drained of mucus and filled with air... and also allowing any germs that you might have breathed to get into them and make what would otherwise only affect your nose into something worse. But why do we have sinuses at all?

Small Cats: Almost a Puma and Not Quite a Lynx

Jaguarundi (grey morph)

As I mentioned at the start of this series, the cat family can be divided into two living subfamilies. The "roaring cats" are all large animals: lions, tigers, leopards and jaguars. The "purring cats", however, are typically much smaller... but there are exceptions. Marginally the largest member of this subfamily is the animal variously known as a puma, cougar, or mountain lion (Puma concolor). These are all the same animal, although the term "puma" is sometimes reserved for the southern subspecies and "cougar" for the northern one(s). They were once found through essentially the whole of the Americas apart from Alaska and central/northern Canada, but, aside from a population of 200 or so "Florida panthers", are now absent from much of eastern North America.

Despite its unusually large size, however, the puma does not represent some early offshoot of the main feline lineage. Indeed, it is more closely related to the domestic cat than it is to, say, the ocelot. The cheetah (Acinonyx jubatus), the only other "purring cat" that comes close to it in size (the females are roughly similar in weight, but male pumas are larger), turns out to be a fairly close relative, despite the cheetah's remarkable specialisations for speed. The closest relative of the puma, however, is a somewhat less well-known animal: the jaguarundi (Puma yagouaroundi).

The Tale of the Tail

The defining feature of vertebrates is that they possess a vertebral column, or "backbone", a series of interlocking skeletal structures that run down the centre of the back and serve to protect the main nerve cord. Unless you're a shark or something of that sort, these structures are made of bone and, at least once we ignore fish and amphibians, there's a reasonably consistent pattern as to how these individual vertebrae are structured.

One of the distinguishing features of the mammal skeleton, however, is that the backbone can be divided into five distinct regions, based on the function and detailed structure of the vertebrae within it. At the front end (or top, if you're bipedal) are the cervical vertebrae, which together form the neck. The first two of these are further specialised, the frontmost one because it has to connect with the skull, rather than to another vertebra in front of it, and the second because it's the pivot that allows the head to turn. Including those, there are almost always seven cervical vertebrae, even in giraffes... although sloths and manatees are exceptions, because of course they are.

Miniature Marsupial Lions

Thylacoleo carnifex

The largest carnivorous marsupial alive today is the Tasmanian devil (Sarcophilus harisii). Noticeably smaller than a European badger, it's still almost twice the weight of the next nearest contender for that title, or, indeed, of the omnivorous Virginia opossum so well-known to Americans. Most other living predatory marsupials can more accurately be described as "insectivores", due to their small size.

Unsurprisingly, this wasn't always so. Most famously, perhaps, there was the thylacine or Tasmanian wolf, which officially went extinct in 1936. There were also the "marsupial sabretooths" of South America, which died out during the Pliocene about three million years ago. However, these are no longer thought to technically be marsupials in the sense of being descended from the last common ancestor of the living species, even if they were definitely in that branch of the mammalian family tree.