Sunday, 23 April 2017

Pinnipeds: Ribbon and Ringed Seals

Ribbon seal (male)
Although there is, perhaps, more variety amongst seals than one might at first expect, when it comes to colouration, there isn't all that much to distinguish the different species. The majority are brown or grey, often with black or pale splotches of some kind. I've already described one exception, the harp seal, but arguably the most distinctive of all seal coat patterns belongs to its close relative, the ribbon seal (Histriophoca fasciata).

Male ribbon seals are black, or very dark brown, with clear, wide bands of pure white fur around their necks, shoulders, and just above the hips. Females are medium-brown with light tan stripes, so the pattern is less striking, but it's still present, and in the same shape. Neither sex is born like this; even once baby ribbon seals shed their pure white fur at around a month of age, they are initially plain in colour, only fully developing the stripes by the time they are two years old.

Sunday, 16 April 2017

Pliocene (Pt 16): The Pliocene Oceans

Over the last two and a half years, I have talked about a range of mammal species found across the Pliocene world. So far, I have only looked at the continents, and the various animals that lived on land. But the Pliocene seas were, of course, equally teeming with animal life. Much of this naturally consisted of either fish (most famously the giant "megalodon" shark) or invertebrates of various kinds. Sea turtles also existed, including some quite large ones, but, in keeping with the scope of this blog, I'm going  to focus on the mammals.

While we often tend to think that prehistoric animals tended to be larger than those alive today, this, was however, rather less true of whales, which have grown more or less steadily in size over the course of their evolution, perhaps in part to make it increasingly difficult for anything else to eat them. So, for example, the Pliocene killer whale (Orcinus citoniensis) was around 4 metres (12 feet) in length, barely more than half that of the modern species - although still quite impressive on a human scale.

Sunday, 9 April 2017

Dolphin Vaginas

If you look at any really detailed description of the physical appearance of a mammal species, you will find a lot of intricate information on the shape of the teeth (especially the molars and premolars) and the dimensions of the skull. There will also be discussions of the shape and proportion of the limbs and the exact colour of the fur, as well as any horns or antlers it might have. And there's a high probability that there will be quite a lot of information about the shape of its penis and the size of its testicles.

Obviously, reproductive anatomy is an important field if we want to really understand how an animal functions and behaves. Testicular size, for example, can tell us about its mating strategies. This is because the rule is not simply "the bigger the animal, the bigger its gonads". In order to gather a harem of receptive females around itself, a male has not only attract them to itself with suitably impressive antlers (or whatever) it also has to fight off rivals, and it's going to have to be big and muscular to do that. But if the females are sexually promiscuous, that's pointless. Instead, what you really need is to produce so much sperm that yours swamps that of your rivals. So, in those species, the males tend to be smaller, but their testicles larger (proportionately speaking). Alternatively, if your species is monogamous then neither of these things are much of a concern.

So male reproductive anatomy can tell us quite a bit. But you won't typically find, in most descriptions, is quite so much information on the female reproductive tract. There's probably some information on the shape of the uterus, which can relate to things like litter size, and maybe for a few other features besides, but it tends to be rather less than you'll find for the males.

Saturday, 1 April 2017

Deadly Demon Ducks of Doom

Since today is 1st April, although I'm not doing a spoof post, I am taking my annual break from mammals to talk about birds. Specifically demon ducks, although I nearly went with flightless boobies. It's that sort of day.

Australia is the most isolated continent to possess native mammals, so perhaps it shouldn't be surprising that the mammals that live there are particularly unusual, often only distantly related to those elsewhere. Birds, however, have an advantage that most mammals don't, in that they can fly long distances between land masses without dying. (They may not be doing so deliberately, of course, but being blown off course in a storm is the sort of risk they have to put up with). It's notable, in fact, that one of the two groups of native placental mammals in Australia are the bats, which are also also found further out in the Pacific islands.

Anyway, the upshot of this is that the birds of Australia frequently fall into taxonomic groups familiar from elsewhere in the world; Australia has owls, doves, seagulls, and parrots, among many others. At the same time, however, it is isolated enough that it does include some unique kinds of bird that are not found on other continents - less than the number of unique mammal groups, to be sure, but a number nonetheless. For example, lyrebirds are endemic to Australia, and are considered to form the oldest living branch of the songbird family tree.

Sunday, 26 March 2017

Pinnipeds: Grey and Harp Seals

Grey seal
There are four different species of seal that live off the coasts of northern continental Europe. Perhaps the best known is the harbour seal, or "common seal", which is also the most widespread of all seal species, being found across both the North Atlantic and the North Pacific. When the scientific naming of species was introduced in 1758, it was the only such species recognised from the area, but it only took a few decades for proper scientific descriptions of the others to follow, recognising that they were distinct from their "common" cousin.

The last of the four to be split off was the animal we now know as the grey seal (Halichoerus grypus), in 1791. While that's still fairly early as such things go, the fact that it was the last of the local seals to be formally identified as something different from the regular sort is likely down to the fact that it does look very similar to the harbour seal. Although, in fairness, it was first named by an entomologist, so clearly you don't have to be a mammal specialist to tell them apart.

Sunday, 19 March 2017

The Giant Chinese Badger-Otter

Otters and badgers are both members of the weasel family, the Mustelidae. As a result, while they are visibly quite different, they have a number of anatomical similarities, reflecting their shared ancestry. Indeed, some of the similarities, such as those in the precise shape of their teeth, are rather greater than one might expect simply from them belonging to the same family. On the basis of this, it was being suggested as recently as the 1990s that otters were essentially aquatic badgers - descendants of early badger species that had entered the water, developing webbed feet, a long muscular tail, and so on, in the process.

We now know, from various genetic and molecular studies, that this isn't so. The closest living relatives of otters are probably the weasels themselves and/or the zorillas and their kin, with badgers representing a rather earlier branch in the mustelid family tree. Given this, the apparent strong similarities between the two are either a case of parallel evolution, perhaps due to the fact that, by the standards of weasels, they're both fairly large animals, or, perhaps more likely, that they are ancient features of the group that happen to have been lost in their other relatives.

Sunday, 12 March 2017

A Side Order of Flies

Most species of bat eat insects, whether caught on the wing or plucked from leaves or other surfaces. But this is by no means true of all species, with the second most common diet - perhaps representing around a quarter of known species - being one based on fruit. Indeed, fruit-eating had evolved more than once among bats, with the giant fruit bats of the Old World not being especially close relatives of the much smaller ones found in the Americas.

While a great many herbivorous and omnivorous mammals include fruit as part of their diet, one estimate is that only around 10% of mammalian species rely on it as their primary source of food - most of them bats or primates. While that's not exactly a tiny proportion, given the number of mammalian herbivores in general, it isn't a huge one either. This, it has been suggested, is because, while fruit are great as a source of calories, they tend not to be high in protein, and a healthy animal needs a supply of both.

In the case of humans, eating plenty of fruit is well known to be a good thing, but trying to eat nothing but fruit for any extended period of time is likely to be a problem. Not only are you likely to suffer from lack of protein in your diet, but you will also suffer deficiencies in certain minerals and vitamins. That one of the main vitamins you would be short of is vitamin D, which promotes calcium absorption in the gut, is a particular problem, bearing in mind that there isn't much calcium in fruit to start with. For this reason, fruit-only diets can be a real problem for children, who need that calcium to grow their bones.

Sunday, 5 March 2017

By the Light of the Silvery Moon

Why bother being nocturnal? Being active only at night makes it much harder to see what you're doing, and while it's possible to develop good night vision to minimise the problem, this is evolutionary costly. Well, if you're a herbivore, the advantage of being active at night is that it's much easier to hide from predators, since, they, too, would have to evolve good night vision to find you. And, if you're a predator, the advantage is that at least some of your competitors won't be around at night, allowing you to snack on nocturnal herbivores and not have to share your food supply.

But this, of course, cuts both ways. For example, while darkness hides you from predators, it also makes it more difficult to spot predators coming if they have seen you. As so often, this leads to a balance, and different species taking advantage of different points on the continuum of possible behaviours.

We can see some of the effects of this in how animals respond to different levels of darkness. Not all nights are equal, after all. The most predictable change is in the amount of moonlight, with the night of a full moon being considerably brighter than a night without a visible moon. Somewhat less predictably, of course, there's the weather, unless, perhaps, you live in a desert where overcast skies are fairly unlikely. So, if you're a nocturnal herbivore, should you be more active on the night of a full moon, or less?

Sunday, 26 February 2017

Pinnipeds: Harbour and Spotted Seals

Harbour seal
When the modern system of scientific names for organisms was devised, and the first recognised catalogue of such things was published in 1758, Carl Linnaeus named four species of seal. Two of these are, for anatomical reasons explained in my previous post, no longer considered members of the "true" seal family. One of the others was the elephant seal, which Linnaeus had presumably only heard of by reputation. The remaining one, however, was likely an animal he was much more familiar with, given that they are found around the coasts of his native Sweden.

In fact, when Linnaeus described what was essentially a typical "seal-like" animal, he would have been thinking of what we now know to constitute, like the "elephant seal", a number of different species. The one that was likely the most familiar to him, however, is the one that retains the scientific name that he gave it, and which is known in many parts of the world simply as "the common seal". In more recent times, the alternative name of harbour seal (Phoca vitulina) has become more widely used, and it's this that I'll use to describe the animal to which, taxonomically speaking, all other seals are in some sense compared.

Sunday, 19 February 2017

Pliocene (Pt 15): Life on the Australian Grasslands

Kolopsis, a diprotodontid
At the dawn of the Pliocene, Australia was a relatively green continent, with plenty of rich, tropical and subtropical, vegetation. That changed as millions of years passed, with the continent becoming steadily drier and the grasslands and semi-desert of the Outback came into being. This was, of course, bad news for many of the animals that had lived there in the wetter past, many of which went extinct, but it also saw a noticeable increase in the number of grazing animals, for which wider grasslands were clearly a boon.

Elsewhere in the world, this sort of thing was benefiting animals such as horses, goats, and antelopes. But Australia was different. It wasn't, of course, the only island continent of the day, but it was the oldest by some margin, having separated from its neighbours long before South America split from Antarctica, or before animals stopped crossing between Eurasia and North America (even ignoring the Ice Age crossings of the Bering land bridge, which were, at this point, still in the future).

Sunday, 12 February 2017

Scaring Off Snakes

Animals would, on the whole, prefer not to be eaten. As a result, they have evolved a number of ways of avoiding this fate. Being particularly large and fearsome is one tactic - very little eats lions, after all - but that obviously won't work for more most creatures. Many other defensive measures are passive, such as camouflage, or involve hiding or only coming out at a time of day when the local predators aren't around much.

An approach that's essentially the exact opposite of camouflage is the "aposematic display", in which the animal has stark, highly visible, colour markings that warn predators it is dangerous. Of course, you really need something to back this up, or the predators will eat you anyway, and, moreover, find you quite easily. Among mammals, among the clearest example of this are the skunks, with their dramatic black-and-white colouring that warns potential predators that they might get a face full of stink if they try anything.

Sunday, 5 February 2017

Pandas in Cages

Zoos have changed a lot since their inception in the 19th century. (Obviously, collections of wild exotic animals have been around for thousands of years, but the first "zoological garden" in the modern sense was arguably London Zoo, which opened its gates to the public in 1848). For a long time, animals were literally kept in cages, the easier for the public to view them. Conditions were, from the animal's perspective, for the most part pretty grim.

There are doubtless many zoos across the world, especially in poorer countries, where things haven't improved all that much. But, at least in the West, things have changed significantly. Animals frequently get the chance to roam in outdoor enclosures with grassy environments, rocks and trees to climb, ropes or other toys to play with, and so on. Furthermore, modern zoos do have an important role to play in issues such as conservation - there are species in the world today that would have gone entirely extinct had not some of them been kept in zoos. (For what it's worth, two mammal species - a deer and an antelope - are currently listed as "extinct in the wild" by the IUCN. Re-introduction efforts are underway for both, but it's a slow and difficult process).

Sunday, 29 January 2017

Pinnipeds: The Difference Between Seals and Sea Lions

Otariid (above) and Phocid (below)
Mammals, being air-breathing animals, mostly live on land. Even when they hunt or graze for food in the water, they generally return to dry ground to do things like sleeping. Nonetheless, an aquatic lifestyle has evolved several times amongst mammals, and four of those lineages survive today. Perhaps the best adapted, because their young are born able to swim, are the cetaceans (whales, dolphins, etc.) and the sirenians (such as manatees). The other two are sea otters and pinnipeds.

There are three recognised families of pinniped alive today: seals, sea lions, and another that includes only the walrus. All are distinguished by having flippers instead of feet, and a lifestyle that requires them to climb out of the water in order to breed and raise their young.

Leaving the walrus aside, the names I've just given to the other two families (and thus the title of the post) are really a bit misleading. This is because a group of animals called "fur seals" actually belong to what I'm calling the "sea lion family" (technically the Otariidae), and in casual usage, the term "seal" is often extended to pinnipeds in general. As a result, if we really want to be accurate, we need some term to distinguish members of the other family from seals more generally. The technical term for these animals is "phocids", but other commonly used terms include "true seals" and "earless seals".

Saturday, 21 January 2017

Fossilised Hedgehog Ankles?

Many moons ago, back when I was at University (and studying zoology formally, instead of just as a hobby), the great majority of invertebrate-eating, non-flying, placental mammals were placed in a single group, the Insectivores. Even then there was some suspicion that this was a bit of a "wastebasket taxon", a group of animals placed together because it wasn't obvious what else to do with them. Molecular phylogenetics and cladistics were still in their infancy in those days, and, so far as I recall, the latter was never even mentioned.

Since then, things have changed, giving us a better picture of evolutionary relationships overall. Among other things, the number of animals that really belonged in the Insectivora was whittled away, as we discovered where the things we'd thrown into the wastebasket really belonged. The rump of the group, a genuine evolutionary unit that now goes by the less accessible name of "Eulipotyphla", does, however, still contain its most familiar members, animals such as shrews, moles, and hedgehogs.

Part of the problem is that these are relatively unspecialised mammals, in the sense that they remain broadly similar to what we think the first ever placentals looked like. Moles, of course, have adapted to a burrowing underground lifestyle that makes them fairly distinctive, but this is rather less true of their relatives. This also makes things difficult when we're looking at fossils, and we're trying to figure out just how far down the placental family tree any given suspected small insectivorous animal actually is.

Sunday, 15 January 2017

Socially Awkward Mice

Many mammals have complex social lives, in which they have to interact with others of their kind in a multitude of different ways. Even those that predominantly live alone still require some degree of social interaction, especially during the breeding season, or when raising young. But for those that regularly encounter other members of their species, social interaction is particularly important, and its sophistication in primates was likely one of the key factors in the rise of humanity.

In the case of humans, of course, much of our social knowledge is built up as children, learning social rules through observation and experience as well as through more explicit instruction. And, while out ability to use language to impart detailed information is something that's essentially unique to us, the need for a suitable environment to fine tune social behaviour isn't something that just arose out of nowhere. Raising an animal in isolation from others of its species might not be as cruel as trying to do the same to a human child, but that's not to say that it wouldn't have some effect on them.

Sunday, 8 January 2017

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.