Oligocene (Pt 2): Europe's Big Break

Eomys

The dawn of the Oligocene is marked by a sudden cooling of the Earth's climate, of which the most obvious consequence was the creation of the Antarctic ice sheets. These locked up so much water that sea levels dropped worldwide, reshaping coastlines. Nowhere were the consequences of this more apparent than Europe, despite its great distance from Antarctica.

Prior to the Oligocene, it would have been possible for a hypothetical traveller to sail from what is now the eastern Mediterranean, through the Paratethys Sea (now the Black and Caspian Seas) due north and into the Arctic Ocean. The body of water that made this possible, the Turgai Strait, was already becoming shallower and narrower as the Oligocene approached, and the sudden dip in sea level finished it off altogether, closing off the sea route that had once run along the eastern flank of the Ural Mountains. 

All the World's Deer: Endangered and Beyond

Eld's deer

A significant number of deer species are endangered. As primarily forest-dwelling animals they are particularly vulnerable to habitat loss, especially in those parts of the world with high human population density and intensive agriculture. Indeed, of the species of deer formally listed as endangered by the IUCN, all but one live in southern and eastern Asia.

Among these is Eld's deer (Panolia eldii), first described by Percy Eld, a British officer working for the Commissioner of Assam, and then more formally written up by army doctor John McClelland in 1842. There is some dispute about the correct scientific name of the animal, due to a number of conflicting studies about where exactly it fits in the deer family tree. It was originally placed in the genus Cervus, along with red deer, but that didn't mean much at the time, since it was 17 years before the theory of natural selection, let alone modern phylogeny. 

Down, Down, Deeper and Down

Ictidosuchoides also survived the extinction

We've all heard of the extinction event that wiped out the non-avian dinosaurs, leaving the mammals free to diversify and take their current role (along with the birds) as the most visibly numerous land-dwelling vertebrates. But this was not the only major extinction event in the history of the Earth.

How many there actually were rather depends on how big one has to be before being considered 'major'. Part of the reason that we can divide geologic history into so many periods and other subdivisions is that many of them ended with an extinction event of some sort, so that the creatures living afterwards looked different from those living beforehand. But that's not always the case, and, anyway, not all extinctions were equally large and dramatic - at least so far as we can tell from the fossils left behind.

Prehistoric Mammal Discoveries of 2017

Albertocetus meffordorum, the post-cranial anatomy of which
was described for the first time this year.

At the end of each year, I do a slightly different post to wrap up the blog for the season. The format of these has changed over the years, and this year, again, it's time to do something slightly different from previous occasions. Not that there haven't been some interesting new species discovered this last year, with, to my mind, the Skywalker gibbon (Hoolock tianxing) being the stand-out example. This was announced early in the year, having been discovered in the Chinese/Myamar border region by a group of researchers who were fans of a certain science fiction franchise ("tianxing" literally translates to "sky-walker" in Standard Chinese), and is likely already endangered.

But this year, instead of discussing just how many new kinds of bat we discovered in the last twelve months, I'm going to note that my posts on fossil mammals tend to be more popular than those on the living sort, and take a look at a partial assortment of scientific papers published on this subject in the last year that, for various reasons, didn't end up in my regular blog posts. So here goes.

Pinnipeds: Decline of the Monk Seals

Mediterranean monk seal
(museum specimen)

The great majority of seal species are found in cold, often freezing waters. Even harbour and elephant seals, which are frequently found in temperate, or even subtropical, climes, also inhabit colder latitudes for at least part of the year. There are just three modern species of true seal that are found solely in warm waters, and they all happen to be closely related. These are the monk seals.

It's not actually known why these animals are called "monk" seals. The oldest known reference to the term comes from Johann Hermann in 1779, when he wrote the first scientific description of the Mediterranean monk seal (Monachus monachus), and gave it its scientific name. The only reason he gave for doing so was that he'd heard that the animal was called that in France, and thought that maybe that was because, seen from behind, the head and shoulders looked a bit like a robed and hooded man. But he was guessing about that latter part, and there doesn't seem to be any independent corroboration that the animal really was called a "monk seal" in France (or, indeed, anywhere else) prior to his naming of it. Presumably, he'd got the name from somewhere, but, for all we know, he might have misremembered the details.

Ice Age Survivors in Hungary

Asiatic wild ass

The end of the Ice Ages saw a number of extinctions sweep across the world, particularly the Northern Hemisphere. Those animals that did not die out as the climate suddenly became warmer often moved further north, changing the composition of the local fauna wherever they had previously lived. This was no "mass extinction" of the sort associated with the end of the dinosaurs, but, on a smaller scale, it was nonetheless significant.

However, as we know all too well, it was by no means the last time that animals went extinct, let alone the last time that they have been eliminated from some local area. Many of these later extinctions were, of course, due to human activity, especially as we colonised new continents or discovered new islands.

But not necessarily all of them, since the climate has not, in fact, remained constant since the Ice Ages ended. After the sudden thaw that marks the boundary between the Pleistocene and the current, Holocene, epochs, warming continued, but slowed. It reached a peak somewhere around 4,000 to 5,000 BC, and then began a slow cooling that has continued almost until the present. Even that cooling trend has had its fluctuations and reversals, most notably the Medieval Warm Period of the 10th to 13th centuries AD.

Bovines: Almost-Cows of Southeast Asia

Banteng female

So far, in my survey of the Bovinae subfamily, I've mostly looked at species that most Westerners are, if not personally familiar with, at least well aware of: domestic cattle, yak, and bison. The exception, perhaps, is the gaur, an unusually large (or, at least, tall) species of bovine native to Southeast Asia. The gaur, however, is not alone, for there are two other very closely related species that are native to the same general area.

The better known of these is likely the banteng (Bos javanicus), an animal that was once found from eastern India to southern China, and across the whole of the Southeast Asian peninsula; there are even distinct subspecies on Borneo and Java. Today, the wild animal is extinct in India and Bangladesh, and found only in a few limited patches elsewhere. It has been formally listed as an endangered species since 1996, but the species as a whole is in much better shape than that would suggest... because this is another species that has been successfully domesticated.

The domesticated animals are known as Bali cattle, and they are in wide use across Indonesia and Southeast Asia. Over the years, a number have escaped from captivity, with the result that at least some feral populations are now found on a number of Indonesian islands that did not (so far as we can tell) ever host the genuinely wild form. More dramatically, British troops took some of them to the Northern Territory of Australia in 1849, but released them all just one year later when crop failure forced them to abandon their new settlement. The resulting feral animals are still there, and, while there are several thousand of them, all in Garig Gunak Barlu National Park near Darwin, since they are descended from just 20 imported animals, it's perhaps unsurprising that they are now highly inbred.

The Dog Family: Raccoon Dogs and the Fate of the Warrah

Raccoon dog

The Wikipedia page on the dog family includes, on its attached discussion page, a complaint that the article includes a picture of a raccoon - an animal that is clearly not part of the Canidae. Except, of course that there isn't (and wasn't then) any such picture. The complainant was looking at a picture of a raccoon dog.

It's an understandable mistake. The raccoon dog (Nyctereutes procyonoides) does look remarkably like its partial namesake. Indeed, the second half of its scientific name, first given to it by John Edward Gray in 1834, actually means "raccoon-like". The effect is achieved primarily by that dark mask over the eyes, a feature we naturally associate with raccoons, although, aside from the lack of stripes on the tail, the rest of the animal is fairly raccoon-coloured as well.

Nonetheless, it is indisputably a dog, although quite how it was related to other dogs was long a source of puzzlement. Modern studies have shown that it appears to be related to the true foxes, albeit not very closely. Its closest relative may, in fact, be the bat-eared fox of Africa, although, again, I should stress that this isn't exactly what you'd call a close relationship... just closer than anything else happens to be.

Weasels on the Riverbank: Mink

European mink

While most are still terrestrial, the long sinuous bodies of weasels are easily adapted to an aquatic lifestyle. Within the lineage that led to the modern weasels and their relatives, semi-aquatic habits have evolved at least three times. The first of those lines led to the otters, but the most recent led instead to the European mink (Mustela lutreola), a much smaller animal that is clearly not an otter, and is, in fact, most closely related to the ferrets and polecats.

The European mink was once found throughout central and eastern Europe, from Germany in the west to European Russia in the east. It is almost as aquatic as an otter, and is never found far from fresh water, preferring dense vegetation along the banks of fast-flowing streams and small rivers. Its feet are partially webbed, and it is a good swimmer in comparison to most other members of its family, although not as skilful as the otters. Mink den in natural hollows, such as those beneath tree roots, and will also take over the burrows of their favourite food, water voles.

Even so, while they are undeniably well adapted to a semi-aquatic lifestyle, they are no match for otters. For example, mink do not see well underwater, and only dive after fish, crayfish, and so on, after they have spotted them from above the surface. Given that otters and mink both inhabit the same parts of Europe, why aren't the latter simply out-competed? It turns out that it's their very lack of adaptation that helps them survive.