Eocene (Pt 2): In the Jungles of Europe

Heterohyus

During the Eocene epoch, Europe was very different from the way it is today. For one thing, it was still separated from Asia, with the Turgai Strait running between the two, roughly from what would now be the Black Sea to the Arctic Ocean. But, were you to look at a map without any modern day context, you probably wouldn't call it a continent, because it wasn't a single landmass, but a chain of large islands.

The biggest of these lay to the north, encompassing Scandinavia and the lands to the east. Just south of that, the second-largest was the one that would later become Britain, France, Germany, and some of their smaller neighbours. A smaller, but still sizable, Iberian island lay to the southwest, and a collection of low-lying ones occupied the south and east, with the more mountainous parts of that region having yet to form.

But, even if you didn't know the changes in the geography, if you could simply travel back in time to the Early Eocene and look around you, it wouldn't feel much like Europe. The continent was closer to the equator than it was now - northern Germany was about where Milan is today - but, even ignoring that, the world as a whole was much hotter. This is part of the reason for the islands, since there were no ice caps back then, but it means that our hypothetical time traveller would be, in almost any part of the landmass, standing in a jungle.

Viverrids: Genets of Central and Southern Africa

Rusty-spotted genet

The genets are one of the most speciose of the carnivoran genera, with at least fourteen species living across Africa and, in the case of the common genet, just beyond it. However, the majority of the species have been little studied. As small, nocturnal carnivores often dwelling in hard-to-reach places, it is relatively hard to do so, and they lack the cachet that applies to larger, more glamorous animals such as cheetahs, hyenas, or even wild cats. 

It probably doesn't help that there is not a great visual or (so far as we know) behavioural difference between them. In many cases, the easiest way to tell them apart is simply to note where they were found. There are subtle differences between them, to be sure, but you may have to look quite closely, and the variations are often matters of degree. Nonetheless, let's see what I can say as I take a look at the seven confirmed species that I didn't cover in the last one.

Rabbits in the Ice Ages

The rabbit (Oryctolagus cuniculus) is one of the more familiar mammal species to most people in the developed world, not least because it has been partially domesticated. Moreover, wild and feral rabbits are found across wide parts of the world, living on every continent except Antarctica. They are adaptable animals, able to survive in a wide range of different habitats, from hot semidesert to forests and bleak moorland. So much so, in fact, that, in most parts of the world, they are a pest.

The rabbit is widespread because we humans have spread it, following the initial domestication event in France, no later than 800 AD. This was originally for meat and fur, with pet breeds appearing only from the late 18th century. Rabbits are now found, for example, on Middleton Island, a chilly speck of land 130 km (80 miles) off the south coast of Alaska, and on the Kerguelen archipelago in the Indian Ocean, which is about as remote a place as it's possible to get.

Running Hyenas of Greece

Chasmaporthetes

Mentioning a "hyena" today likely brings to mind the image of a muscular, aggressive, scavenging creature, probably with a spotted coat. This, the spotted hyena (Crocuta crocuta), is, however, only one of three species alive today, with the two lesser-known ones being smaller and less aggressive. In fact, the hyena family includes a fourth living species as well, although this isn't always referred to as a "hyena" because it's really only dangerous to termites and can't crack bone like "true" hyenas can.

Four living species isn't very many for a family of mammals but, like many other such small groups, there is a long fossil history that includes a great many extinct forms. These varied in form even more than the living species do. At one extreme are animals larger and stronger even than the living spotted hyena, while at the other (all living very early on) are small tree-climbing animals that looked more like civets. 

Somewhere in between are the "running hyenas".

Viverrids: Genets of Northern Africa (and beyond)

Common genet

At the dawn of scientific taxonomy in 1758, the group of animals that would later become the civet family included four species that we still recognise today. Two of these - skunks and mongooses - were later moved elsewhere, and one of the others was, of course, the defining species of the family, the large Indian civet.

The other was the common genet (Genetta genetta). Frédéric Cuvier split the genets off from the civets proper in 1816, recognising just one other species - which molecular evidence has since shown isn't a viverrid at all, although this wasn't obvious even in the late 20th century. His basis for the distinction was that genets have a much smaller scent gland than civets, although he conceded that the secretions it produced were, in his words, "très manifeste". 

Just Cold Enough

Northern meadow jumping mouse

Hibernation is one of the most effective means that mammals can employ to withstand harsh winter temperatures. Many mammals, especially larger ones, use other means, such as growing a winter coat, caching food, or simply moving somewhere warmer, but, if the goal is to reduce energy requirements when you can't get out to feed, hibernation is the most effective means of doing so.

During hibernation, bodily metabolism slows right down, so that an animal may need as little as 1% of its usual calorie supply to stay healthy. This has negative consequences, so that the animal does need to wake at intervals to stave them off, and how often this happens varies from species to species. In this respect, true hibernation can be distinguished from shorter, often daily, bouts of torpor by the fact that each "sleep" can last for weeks or even months. 

Staying Away from the Boys

Many large, hooved mammals live in herds. This has obvious advantages of safety in numbers, spreading the work of looking out for predators, as well as benefiting from the knowledge of more experienced herd members as to the best places to find food or shelter. The structure and composition of these herds vary from species to species, but one common trait is that males and females often form single sex herds that travel apart for much of the year.

This is referred to as "sexual segregation", and was first formally described by Charles Darwin in The Descent of Man. It isn't unique to mammalian herd animals, being seen in everything from fish shoals to bird flocks, as well as in non-hooved mammals (dolphins, bats, primates, etc.) Most zoological research, however, has tended to focus on large cloven-hooved mammals, such as deer and antelopes.