Sunday, 20 August 2017

Mice, Mice, and More Mice

A common feature of my blog posts, pretty much since the beginning, has been the inclusion of cladograms, tree-like diagrams that show how different species, or groups, of mammal are related to one another. Our knowledge of these relationships is constantly evolving, as we get more and more information, or find different ways of doing the necessary measurements.

In general, though, what happens is that scientists measure a number of different features from the animals that they want to study, and compare which ones have the most in common. These days, these are most likely to be physical measurements, such as fine details of the shape of the skull or teeth, if at least some of the creatures we're looking at happen to be fossils. Otherwise, it's much more likely that the things being compared are stretches of genetic code. The further apart two animals are, evolutionarily speaking, the more differences there are likely to be, and if we pick a gene that both animals possess, and that can accumulate a reasonable number of changes without stopping working altogether, we have a good basis for comparison.

Sunday, 13 August 2017

Pinnipeds: The Mighty Elephant Seals

Northern elephant seal (male)
The largest of all seals are, of course, the elephant seals. These were one of the original species of seal to be scientifically named, back in 1758. They were originally given the name Phoca leonina, which literally translates as "seal-lion", suggesting some possible confusion on Linnaeus's part about which exact animal he was describing. For a long time, it was thought there was only one species, but we now know that the populations in the Northern and Southern Hemispheres represent two different, but closely related species.

Northern elephant seals (Mirounga angustirostris) live off the western coast of North America, with breeding colonies on offshore islands and occasional isolated patches of continental coast in California and Baja California. It's probably here that they are more commonly seen, since they not only spend the winter breeding season ashore, but they also visit the same beaches during the summer for their annual moult, when they are unable to enter the water for weeks at a time. Surprisingly, then, they spend the rest of the year somewhere else entirely, travelling hundreds of miles from their colonies to feed in the north-east Pacific, and spending spring and autumn as far north as the Aleutian Islands and, on occasion, as far west as Hawaii. Quite why they'd do something as seemingly daft as to make the same long-distance migration twice a year isn't entirely clear, although it presumably has something to do with the ideal weather for each activity.

Sunday, 6 August 2017

Bed Time for Wild Hamsters

Golden hamster
After the mice, the second largest family of mammals is the hamster family, with somewhere in the region of 600 known species. The vast majority of these species are, however, not hamsters, and I refer to it as the "hamster family" only because that is the literal meaning of its scientific name, the Cricetidae. Over half of the cricetids, for instance, are "New World mice" visibly more or less indistinguishable from the "true" mice of the Old World. Most of the remainder are voles, and a mere couple of dozen or so are actually hamsters.

The species most people think of when they think of hamsters is the golden hamster (Mesocricetus auratus), which is the animal commonly seen in pet shops. While a few other species are sometimes also kept as pets, most of the varieties named on the basis of things such as hair colour and length are just domesticated breeds of the golden hamster. They are found in the wild only in one relatively small area on the Turkish-Syrian border, just north of Aleppo. Which, right at the moment, does make it somewhat difficult to study their behaviour in their natural environment.

But then, given that there are so many of them in captivity, and that they aren't exactly obscure animals, you might think that we know pretty much all there is to know about them. Certainly, compared with many other species, they are well-studied creatures. Indeed, they are common laboratory animals, due to the ease of breeding them in large numbers and their apparent comfort in indoor environments. On the other hand, while there are obvious advantages, such as not being eaten by predators, hamsters do not naturally live in cages... so maybe they behave differently when given the free run of the countryside?

Sunday, 30 July 2017

Miocene (Pt 2): Before There Were Mice

Heteroprox
After a brief cold snap at the very dawn of the epoch, the world of the Miocene warmed rapidly. Europe became, if not truly tropical, at least subtropical, with the interior covered by great forests of oak, laurel, and cinnamon, with magnolia and figs joining pine trees in the highlands. Along the coasts, the hot, damp, climate encouraged the growth of mangrove swamps and palm trees as warm sea currents flowed in from the Indian Ocean - still connected to the Mediterranean at this time. With no ice caps at the North Pole, and relatively few at the South, sea levels were much higher, and parts of continental Europe may, in those days, have still been islands. Certainly, Aqutaine in south-western France and the lower Rhône valley in the south-east were shallow bays stretching some way inland, as was what is now the Tagus valley in Spain and Portugal.

This rich and verdant landscape was home to a wide range of animals, many of them survivors of even earlier times. Many of these, such as the tapirs, didn't survive long in Europe, but a great many did, with musk deer, pigs, and rhinos dominating the herbivorous fauna, and animals less familiar to modern eyes taking the lead among the large carnivores.

But then, as now, the great majority of mammal species were small. While the sight of Diaceratherium rhinos wallowing in the lush swamps of the Swiss shoreline is the sort of thing that would draw the immediate attention of a time-travelling tourist, there was also plenty going on underfoot. Yet the two most common groups of small non-flying mammals that we have in Europe today - the mice and the voles - did not yet exist. So what was there?

Sunday, 23 July 2017

Is the Dormouse an Endangered Species?

At first glance, this seems a fairly daft question. A moment's search on the internet will reveal that only is the dormouse not an endangered species, it isn't even under any significant threat of becoming one. It's about as safe as any species that doesn't specifically rely on human beings can be. There is no risk that we are going to, at any point in the foreseeable future, even come close to running out of dormice.

Look past the headlines though, and things do become a little more complicated. No, the dormouse is not an endangered species, but its population is under threat in certain parts of its range, particularly in the northwest. Some of these populations are isolated from the main bulk of the species in mainland Europe by the presence of various seas, and perhaps the most obvious of those is the British population. Since this population lives on a (relatively) northerly island, and since there are, apparently, risks to the dormouse in the north of its range, it is, in fact, reasonable to ask whether or not the dormouse is an endangered species in Britain.

Sunday, 16 July 2017

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.

Sunday, 9 July 2017

First and Last of the South Asian River Dolphins

South Asian river dolphin skeleton -
note the strange shape of the skull
Although the whales are undeniably spectacular, the majority of cetacean species are much smaller; the sort of animals we generally refer to as "dolphins". The great majority of these belong to the family Dephinidae, variously termed the "oceanic dolphins", "pelagic dolphins", or even "true dolphins". This is a large family, with nearly forty species, including killer whales and pilot whales alongside their smaller kin.

Whatever we call this family, it, in turn, belongs to the larger group of the "delphinoid cetaceans", which also includes the six species of the porpoise family and two other whales - the narwhal and beluga. Taken together, these animals and their extinct relatives have dominated the count of cetacean species across the world for millions of years, forming a key part of the ocean ecology. Of all the other cetacean groups, only the mysterious deep-sea beaked whales come close in terms of the number of species, and even they don't appear to be as varied.