Prehistoric Mammal Discoveries of 2019

Nehalaennia, an 8 million-year-old rorqual
from the Netherlands, first described this year

As the year - and decade - approach their inevitable conclusion, it's time again to look back at a few palaeontological findings of 2019 that didn't, for whatever reason, make it into the regular Synapsida posts. As always, there is no theme to this list, just a sample of what seemed interesting linked only by when it happened to be published.

Small British Mammals: Moles

If hedgehogs are generally welcome in suburban gardens, there's one native British animal that generally isn't, and, like the hedgehog (and shrews) it belongs to a group of insect-eating mammals technically called the Euliptophyla. This, of course, is the European mole (Talpa europaea), sometimes called the "common mole" if we even need to distinguish it from other kinds of mole at all.

As the name implies, European moles are essentially unique to Europe. They are found throughout much of the continent, from northern Spain, Italy, and the central Balkans in the south to southern Sweden and Finland in the north. They are not found in southern Russia, but do reach just beyond the boundary with Asia in the northeast. While they are not native to Ireland, they are found on a number of smaller islands off the coasts of England, Scotland, and Denmark.

Miocene (Pt 17): A Diversity of Dogs

Eucyon

As North America dried out in the Late Miocene, and slowly transitioned towards the deserts and open grasslands that became dominant across the central parts of the continent, it wasn't just the herbivores that were forced to adapt. Carnivores may not have been affected so directly, but, if their food source was changing, they had to do so too.

There were two particularly significant changes among the North American mammalian carnivores that took place around this time. One was the extinction of the bear-dogs, a group with a long history on the continent that was, by this time, typified by relatively large animals that would have looked more like bears than dogs (although they were neither). Over in Europe and Asia, the bear-dogs survived for rather longer, although even there they struggled...  but in North America, the changes were too extreme for them to cope with, and they died out as the Late Miocene dawned.

Small British Mammals: Hedgehogs

There can be few British mammals more distinctive and well-loved than the hedgehog. Indeed, a 2016 poll found that it is, by a substantial margin, Britain's favourite mammal. (For what it's worth, and by a similar margin, the robin is apparently our favourite bird).

The animal that Brits simply call "the hedgehog" is more accurately the European hedgehog (Erinaceus europaeus), and it's found through pretty much the entirety of western Europe. In fact, across much of the continent, the eastern border of its occurrence is very roughly where the old Iron Curtain used to be. That's a simplification, of course, and aside from some border regions of former 'Eastern Bloc' countries, they are also found quite extensively in the Czech Republic, Estonia and parts of north-west Russia. They are also common on several larger islands, including Ireland, Corsica, Sardinia, and Sicily, and, in more recent times, they have been introduced to the Azores.

Don't Sleep with Your Sister

Conservation of mammals (or other animals) isn't simply a matter of providing enough suitable habitat for them to live in. One other consideration is that that habitat should not be overly fragmented - and this can be a problem as we build roads or other transport networks that cross otherwise wild terrain. The problem with fragmented habitats is that, even if there is enough space and food to support a small population of the animal in question, that population cannot reach and interact with other populations. And this leads to inbreeding.

We have known that inbreeding is a bad thing in animals since... well, probably at least since we started domesticating livestock. In our own species, there's a natural revulsion against incest, something that's reflected in moral teachings that go back at least as far as the Old Testament, and similar codes in other cultures. Animals too, avoid inbreeding when they can, perhaps finding the scent marks left by genetically similar individuals to be unpleasant.

Small British Mammals: Water Shrews

Two of the three species of shrew found in Britain are very similar to one another in appearance and habits. This is hardly surprising, given how closely related they are. The odd one out, however, is not quite such a close relative, and is rather more distinctive.

This is the Eurasian water shrew (Neomys fodiens), which unsurprisingly, is simply called the "water shrew" in Britain. Despite its differences, even at first glance, it's pretty obvious that it is a shrew: it's a small, long-tailed animal with short fur, tiny ears, small eyes, and a narrow, pointed, snout filled with sharp teeth. However, by the standards of shrews, it's unusually large. Fully grown adults can reach as much as 10cm (4 inches) in length, and weigh up to 25g (0.9 oz.), closer in size to a typical mouse than to other native shrews.

Bat Poo and Fig Trees

Seba's short-tailed bat (Carollia perspicillata)
feeding on wild pepper

If the presence of plenty of carnivores is generally bad news for herbivores, it may seem that the presence of plenty of herbivores is bad news for plants. Clearly, such problems as over-grazing do exist, but the reality can often be more complex. Fruit are a particular case in point.

Many fruits are tasty specifically to encourage herbivores to eat them, containing highly resistant seeds that pass through the herbivore's digestive tract, land in a nice pile of manure, and germinate to create more plants in future. It has been estimated that, in most wild forest environments, anything from 45% to 90% of tree species bear edible fruit of this kind. (Of course, a number of the fruits we see in supermarkets are even tastier, because we've bred them that way, with the banana being perhaps the most extreme example. But it's not as if wild apples and oranges, for example, don't exist and aren't attractive to animals).

Not all herbivores eat these kinds of fruit, as opposed to other things that botanists would call "fruit", such as grass seeds. Primates are one of the more obvious examples of mammals that do, and it's theorised that our unusually good colour vision arose in part so that we could easily tell which ones were ripe. But another group of mammals that eat a strongly fruit-based diet are, unsurprisingly, the fruit bats.

How Sloths Turned Upside Down

One of the things that sloths are noted for is spending a lot of time hanging upside down. This isn't, of course, something they literally spend their entire lives doing; they come down out of the trees to defecate, and they do sometimes travel over the ground - or swim across rivers - to move from one tree to another. They have also been observed, especially in zoos, casually sitting about in what we'd consider a fairly normal posture. But even so, being upside down is how they spend most of their time.

This is obviously pretty odd, from the perspective of a mammal (or, indeed, most other animals). You might think that what must have happened is that, at some point in the distant past, some ancestral tree sloth first headed up into the branches, decided to do so by hanging from them rather than by the more obvious method favoured by (say) primates, and that all of its descendants simply happened to do the same thing. In other words, it's a one-off quirk of evolution.

Except that can't be right.

The Smallest British Mammals: Shrews

Common shrew

For some reason that I no longer recall, a picture of a shrew cropped up while I was talking with a friend on the internet. "That's a mouse," she insisted. "No," I said, "it's a shrew." "Mouse!"

It was only later that I remembered that the German word for "shrew" is spitzmaus (literally "sharp/pointed mouse") and, since my friend was Austrian, she wasn't necessarily entirely wrong. From a certain perspective, perhaps to German-speakers, all these small, furry, long-tailed things are mäusen.

And it's certainly true that shrews do look, superficially, quite like mice. They tend to be smaller, with narrower snouts, and very small ears and eyes, but there is something quite mouse-like about them. Nonetheless, shrews (unlike, say, voles) are not rodents. In fact, as placental mammals go, they aren't even particularly related to rodents - humans are more closely related to mice than shrews are.

The Curiosity of Lemmings

The reason that there are so many different animal species in the world is that they all have different living requirements; it's no secret that a tiger has different needs from a hedgehog. In most land-based habitats, we can look around and see a fair variety of mammal species and it's obvious that, while they may compete in other ways (by eating each other, for example), they can all survive because they are using their chosen habitat in different ways.

But, in some cases, it's quite hard to find more than a handful of species - especially if we're going to restrict ourselves to mammals, and ignore all the birds, insects, and so on. This is often true of city centres, for example, where you may not have much aside from rats, mice, and urban foxes. But in the wild, however, we are typically talking about particularly marginal habitats, such as deserts, high mountains and other desolate wastes.

A Hole of Your Own

Many animals dig burrows for shelter, whether from the weather or from predators. In some cases these are complex or extensive burrow systems, such as we find with rabbits or gophers, and some animals, such as moles, try not to leave their burrows at all, adapting to a subterranean life. Most are much simpler than this, a basic hole in the ground in which the animal can rest securely at night - or during the day, as the case may be.

At the opposite extreme to the specialised diggers, however, are those animals that don't dig burrows at all, but still find it useful to seek shelter in this manner. These are creatures that will either use natural cavities or take over an abandoned burrow originally dug by something else. If they can't find one, it's usually not a disaster, although it may make life a little uncomfortable. But that's not necessarily true when it comes to time to breed.

Small British Mammals: Hares

Brown hare

The most visited post on this blog remains that explaining why rabbits are not rodents (their incisor teeth may look like those of rodents, but there are differences, and they have an extra set). I've also discussed, briefly, how rabbits manage to digest tough plant matter without the extra stomach chambers found in cows and similar animals by using the large bowel as a second stomach, and then eating the food twice.

All of these things are, of course, also true of the close relatives of rabbits, hares. There are two species of hare living wild in Britain, of which the more common is the European or brown hare (Lepus europaeus).  Like rabbits, they were only introduced to Britain during, or perhaps slightly before, Roman times, but they are now widespread across England, Wales, and Scotland.

Miocene (Pt 16): Giant Camels and High Llamas

One group of animals that you might expect to have done reasonably well as the climate dried out in the later stages of the Miocene epoch were the camels. Camels, of course, are not found wild in North America these days, but, back in the Miocene, it was the only place that they were found, having first evolved on that continent millions of years before.

Indeed, camels had been diverse in the Early and Middle Miocene, inhabiting a number of habitats that we would not associate with the animals today. Once those habitats changed with the shift into the Late Miocene, however, many of them failed to adapt, and a number of earlier forms died out. These included the stenomyline "gazelle-camels", the short-legged miolabines, and the floridatragulines, which had been adapted to the subtropical forests of the southern coasts.

Unravelling the Bushbuck

Imbabala

Three years ago, I wrote a series of posts on the various species of bovine. This was using 'bovine' in the wider, technical, sense than it's everyday meaning, essentially including all animals more closely related to cows than to sheep or goats. This obviously includes all the really close relatives of cattle - bison, buffalo, yak, and so on - but it also includes a number of animals that are more accurately described as 'antelopes'.

Most species of these 'bovine antelopes' belong to the genus Tragelaphus, collectively known as 'spiral-horned antelopes'. Especially if we include the large cow-like elands (sometimes given their own genus, Taurotragus) these are a fairly diverse range of animals, including some adapted to open woodland or savannah, and others adapted to dry scrub, mountain slopes, dense jungle, or swampland. Perhaps because it seems to be the most adaptable of the species, the most widespread of the spiral-horned antelopes is the bushbuck (Tragelaphus scriptus).

Small British Mammals: Rabbiting About Rabbits

Over the course of the last two thousand years, a number of native British mammals have been driven to extinction. These were mostly the larger ones that were considered either dangerous (wolves) or tasty (wild boar). But we have also managed to introduce a few, mostly smaller, animals that were not originally native to the islands but are now widespread. The grey squirrel, being relatively recent, is probably the best known of these, although the brown (or "sewer") rat is another, only arriving in the 16th century.

Another example was first introduced in Roman times, and so has been here rather longer - but, still, it could be argued that it's not technically native. This is the rabbit (Oryctolagus cuniculus).

The Many Kinds of Extinct Marsupial

Simosthenurus, a short-faced kangaroo

Last week, I looked at the diversity of marsupial species that can currently be found in the world and, in particular, how the increasing use of molecular analysis over the last quarter-century or so has improved our understanding of their relationships. We don't have such an advantage when it comes to looking at fossil species and it doesn't help that the fossil record is necessarily incomplete. Indeed, the latter is particularly true in Australia, which, perhaps partly just because it's a smaller continent, doesn't have as wide a selection of rock deposits of the age we're interested in here as some others do.

Nonetheless, because marsupials have been around for a very long time, we do know a fair bit about their fossil history. So, with the aid of the same review that I used last week, let's take a look at some of the kinds of marsupial that are no longer with us.

The Many Kinds of Living Marsupial

Ringtail possum
Because not every animal in Australia wants to kill you

This blog probably wouldn't exist were it not for the fact that there are a great many different kinds of mammal alive in the world today. Most of these are placental mammals, giving birth to (relatively) fully formed young that have been nourished by a placenta in their mother's womb. A significant minority, however, are marsupials, which belong to a separate evolutionary line that split from the placentals long before the dinosaurs died out.

Marsupials are diverse animals, in many cases, paralleling their placental counterparts in some key aspects of their anatomy or behaviour. True, they are not quite as diverse as their placental kin - there are no marsupials bats or dolphins, for instance. There are around 350 known living species of marsupial, commonly grouped into 19 "families", and, while is this undeniably small compared with the 5,000+ species and 120 or so families of placentals, it's hardly insignificant.

Small(ish) British Mammals: Beavers

There are, arguably, a couple of reasons why beavers don't really belong in this series on the small native animals of Britain. So far, I have looked at mice, voles, rats, and squirrels, all of which are undeniably both small and British... but they are also all rodents, and so I may as well complete the set of such animals by including the one that isn't really all that small.

Indeed, weighing in at around 15 to 20 kg (33 to 44 lbs) on average, and occasionally a fair bit larger, the Eurasian beaver (Castor fiber) ties with its American cousin for the honour of being the second-largest living rodent, after the capybara. It is also, of course, a very distinctive animal, and one whose general appearance most people are surely familiar with.

Yin and Yang in the Bat World

"Yin", if you're wondering...

Although the term is used more casually in everyday English, in scientific terminology a "family" of animals is a specific rung on the taxonomic hierarchy. Cats (Felidae) are a family, but otters (Lutrinae) are just a subfamily within the larger weasel family. In turn, families are grouped into "orders", and the great diversity of mammals is indicated by the fact that the standard modern scheme recognises no less than 27 living orders of mammal.

In terms of the number of known species, the second-largest order of mammals, after the rodents, is that of the bats. There are over 1,400 named species of bat, currently grouped into at least 18 different families. Yet they're probably also the least studied of the major mammalian orders - although, to be fair, this may depend on your definition of 'major'. Compared with primates, or hoofed or large carnivorous mammals, we know relatively little about their evolution, and how the various sub-types of bat relate to one another.

Miocene (Pt 15): The Coming of the Rain Shadow

Ramoceros

As the world passed into the Late Miocene, worldwide temperatures dipped from the high summer of the Middle Miocene towards... well, if not autumn, perhaps a late summer, since the world was still overall, probably warmer than it is today. For North America, however, perhaps a more significant effect was caused by the slow shuffling of the continents. A large chunk of rock that corresponds, broadly speaking, to present-day California began to tilt, causing the eastern edge to rise up.

We're not talking a huge tilt, of the sort that you'd notice if you were standing on it - it's been estimated that the eastern end was rising by somewhere around 0.25 mm (1/1000 of an inch) per year relative to the western one. Give it a few million years though, and that starts to be noticeable. While this process really only accelerated during the subsequent, Pliocene, epoch, even at this time, the rise of the eastern end of that block of crust was slowly, but surely, creating what we now call the Sierra Nevada Mountains.

Small British Mammals: Squirrels

Red squirrel

The majority of rodent species look, more or less, like mice or rats, depending on their size. But there are a number of exceptions among the many, many, kinds of rodent in the world. Probably the best known such exceptions in Britain are the squirrels.

By far the most common tree squirrel in Europe, and perhaps the most widespread species of squirrel anywhere in the world, is the red squirrel (Sciurus vulgaris), sometimes called the "Eurasian red squirrel" to distinguish it from the North American animal of the same name. This lives almost everywhere in Europe, apart from the Mediterranean islands, southern Greece, and Portugal, and is one of a relatively small number of native wild mammals in Ireland. Further east, they inhabit just about every temperate, forested, region of Asia, reaching as far as Korea, northern Japan, and the coast of the Bering Sea.

About twenty different subspecies are currently recognised, but there seem to be few reliable ways of distinguishing between them. For instance, while most red squirrels are, in fact, red, a significant proportion are darker, or even near-black. These are apparently more common in the dense highland forests of the Alps and the Altai Mountains, but are not a reliable indicator of subspecies, since they are found in other populations, too.

Being Top Cat

If you happen to own a cat, especially an un-neutered male, you may have noticed that they sometimes pee on things. Shocking, I know.

Spraying is just one way that cats leave scent marks, whether to warn other cats away from 'their' territory, or to advertise their availability to members of the opposite sex. And, as we'd reasonably expect, this is as much true of large wild cats as it is of the domestic moggy. Indeed, we have a reasonable understanding of how some wild cats use these markings. For instance, we know that, just as in the domestic animal, male North American cougars spray more than females, both to mark their territory and to advertise for females.

Small British Mammals: Dormice

Hazel dormouse

The general body plan of looking like a mouse or rat is one that's proven very successful for rodents; a huge number of rodent species, not all of which are closely related, broadly fit this description. Both the mouse family and the "hamster family" (which includes deer mice, pack rats, and voles, among others) are considered to be part of a larger grouping of related rodent families called the Myomorpha. This roughly translates as "mouse-like rodents" and it's a group that includes, under the most common current system, seven different families.

Historically, the Myomorpha was defined based on the structure of the jaw muscles, so that it included some animals, such as jerboas, that don't necessarily look all that much like regular mice. But modern genetic analysis has shown that this anatomic feature isn't as unique as we'd thought, and seems to have evolved at least twice, perhaps in response to a similar dietary requirement in the two different groups. As it happens, the jerboas got to stay in the "mouse-like" group (if only just), but one family of animals that manifestly do look like mice turned out to be something else entirely, and about as unrelated to true mice as it's actually possible to be among living rodent species.

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.

Small British Mammals: Bank Voles

I had intended to wrap up voles a couple of weeks ago, but it turned out that there was so much to say about water voles in particular that it made more sense to add in an extra post to cover everything else. So, here we are with the fourth and final species of vole found in Britain: the bank vole (Myodes glareolus).

Although water voles are more closely related to common voles and their kin than the bank voles, it is the latter that have the closest physical resemblance. While most voles are broadly similar in shape, bank voles are also roughly the same size as the common and field voles, and can be distinguished (without close examination of the skeleton) by the fact that the fur on their backs typically has a distinct reddish tinge. A few instances of individuals with other colours have been noted - including a pure white one that had somehow survived to adulthood without being eaten - but these are rare.

The Last of the Chinese Zebra-Donkeys

Asian wild asses

With the exception of our own species, few mammals have been the subject of quite so much interest in their evolutionary history as the horse. The number of named species of fossil horse far outweighs the number of species that are alive today. A great many of these are, of course, the older three-toed horses, with all living horses being placed in the single genus Equus.

Today that genus consists of just seven widely recognised living species. But, even among just this genus, and ignoring all the older, extinct ones, there were once many more species than there are today. But just how many is that? That's a matter of considerable confusion and debate.

In a way, that's hardly surprising, especially when you consider the focus of attention that there has been on horse evolution. Even just looking at the living species, not everyone agrees that 'seven' is the appropriate number, with some authorities arguing that particular subspecies are distinct enough that they should really be species in their own right.

Small British Mammals: Ratty and the Water Voles

Four different species of vole live wild in Britain, with, perhaps, the field vole being the one that is most typical of the wider group. However, it's perhaps a different species that has the most claim to fame, appearing as one of the central characters (confusingly named "Ratty") in the popular children's book The Wind in the Willows.

Ratty is a water vole (Arvicola amphibius), an animal with a number of differences from common and field voles, despite being fairly closely related to them. Before discussing the species in more detail, we should acknowledge that, over the years, there has been considerable confusion as to what the scientific name of this animal actually is - and, for once there's quite a good reason for it.

Miocene (Pt 14): Sabre-toothed Sea Otters

Ysengrinia

When bears first entered North America is really more a matter of definition than of our understanding of the fossil evidence. Going by what is probably the most common current definition, bears first appeared in Europe about 20 million years ago, in the form of Ursavus elmensis. Noticeably smaller than modern bears, this developed into a number of species across Europe and Asia, and to the closely related Ballusia in China.

Almost immediately, however, Ursavus also crossed into North America, probably arriving around 19 million years ago. It seems to have been far less common there than it was in Europe, with the local species, Ursavus pawniensis (there were probably others, but that's the only one we know of for sure) living in relatively small populations across the west, from Nebraska to Oregon and Saskatchewan. It doesn't appear to have left any descendants, being eventually replaced by more modern species of bear from Asia rather than evolving into anything uniquely American.

The Porcupine Sleeps Tonight

The book All Yesterdays presents, among other things, unusual, but scientifically plausible, depictions of dinosaurs and other prehistoric animals. One picture, for example, shows a T. rex asleep - something that they must logically have spent quite a lot of time doing despite the fact that typical dinosaur books never show it.

Well, it's not as exciting as fighting a Triceratops.

In general, though, even when it comes to living animals, it's probably fair to say that behavioural scientists don't spend a lot of time thinking about how they sleep. All animals advanced to have a brain sleep in some fashion, so far as we know, and obviously, that includes mammals. To be sure, this isn't terribly obvious in the case of dolphins and the like, since they can be both asleep and awake at the same time, but everything that lives on land has to take a nap from time to time.

Screaming Monkeys

Animals, mammals included, produce a wide range of different sounds. Some species are relatively silent or have a very small repertoire of calls, but others are much more vocal, being able to tailor the nature of their call to a specific purpose. Cetaceans and primates are perhaps the most obvious here, but it's worth noting that cats, for example, can purr, mew, hiss, chatter, growl and (in some species) roar.

Some of these sounds - such as a cat's purr - are found only in a single group of related animals. (Not all wild cat species purr, of course, but many do). Others are, at least in general terms, produced by a range of different species, often in quite similar circumstances. One of these is the 'scream', an unusually loud call that is typically high-pitched. Screams also commonly include rapid, chaotic, changes in frequency and amplitude that we humans interpret as a harsh, inherently unpleasant, sound - and there's likely good reason for that.

Small British Mammals: Common and Field Voles

Field vole

In many respects, voles are extremely similar to mice. In many languages, the local word for 'mouse' also describes voles, and this was even the case in English prior to around the 19th century, when the term "vole-mouse" was borrowed from a now-extinct Scandinavian tongue, and shortly thereafter abbreviated to simply "vole". In its original language, it literally meant "field", and a similar etymology can be seen in languages such as German (Feldmaus) and French (campagnol) among many others.

Scientifically, voles have also been mixed in with the mice at different times. While they have recognised as a distinct group with their own scientific name since 1821, for much of the 20th century they were considered a subgroup within the wider mouse family. That's really only changed in the last 20 years or so, as genetic and biochemical evidence has shown that the two groups, while related, have distinct evolutionary histories.

The Big African Not-a-Lion

Spot the real lion

When it comes to fossil animals, there can be little doubt that the ones most popular with the general public are the large ones. There's a reason that dinosaurs seem to hold the most enduring fascination, and that even popular science books about the whole range of prehistoric life are almost bound to have them as part of their title. (And, while some dinosaurs were small, most of the ones we know about weren't, perhaps partly because it's easier to preserve large solid bones than small fragile ones).

It's not really any different with prehistoric mammals, with mammoths, mastodons, and sabretooth cats being the ones that most people would instantly recognise and be familiar with. Even dire wolves, which weren't really all that big, are surely better known than, say, extinct foxes or weasels of the same age. Which brings up a second point: even if an animal isn't as large as an elephant or Diplodocus, being unusually large for a carnivore will still help its public profile enormously.

Lots of Little Deer Mice

If a sexually reproducing animal is to preserve its species without population loss, each pair of parents has to produce, on average, two offspring that will themselves live long enough to reproduce. This is just basic arithmetic, but there are at least three different ways that an animal can achieve this result and which one is used varies from species to species.

One approach is to maximise the chances of each of your offspring surviving. This is called the K-selection strategy, and results in the population being as close to the maximum capacity of the local habitat as possible. (The 'K' stands for 'capacity'... in German). Such animals don't need to reproduce very often, or produce very many offspring when they do, but they have to invest a lot of resources in their survival. They tend to be relatively large animals, with few predators... elephants, primates, and whales are all good examples among mammals. Humans are a particularly extreme example, given how long it takes us to raise our children, and, as with other strong K-selectors, twins are rare in our species.

With a Little Help from My Friends

There are a number of disadvantages to living in groups. Some of the more obvious are that the group will be, collectively, easier for predators to spot, and that they will all have to compete for the same resources. Other problems, which might be less obvious, include the fact that infections and parasites are more likely to spread amongst a group of similar animals that remain in close contact. All of these are good reasons for solitary living, as seen in a great many mammal species.

Despite which, of course, there are many mammals that do live communally. For these animals, whatever costs there may be are obviously outweighed by the benefits, of which there are several. While a large group of animals may be easier to see, it's also easier for them to keep a lookout, since not everyone needs to be actively scanning the horizon (or whatever) all of the time. They can also share in communal tasks, such as child-rearing, putting less strain on the individuals. Predators that hunt in packs can take down prey far too large for any one of them to kill on their own. Even huddling together against the cold can be a worthwhile benefit.

Small British Mammals: Rats!

Brown rat

The term "rat", as commonly used, has no defined biological meaning. A "rat" is simply any rodent that looks at least somewhat like a mouse, but is larger. Animals fitting this description have evolved multiple times, so that rats do not form a single evolutionary group, and not all of them are even members of the mouse family.

Nonetheless, there is a biological group that we can call, for lack of a better term, the "true rats" (technically the "Rattini") which includes the animals that most people likely think of when the term "rat" is used without further qualification. There are two species of this kind of animal in Britain, not least because both of them are found just about everywhere else as well.

Miocene (Pt 13): The Time of No Cats

Aelurodon

Today, there are a number of native cat species in America. The North has its bobcats, lynxes, and puma/cougar/mountain lions while, further south, there are even more species (ocelots and jaguars being merely the most obvious). At the dawn of the Miocene, 23 million years ago, however, it was a somewhat different story.

While there was nothing similar in the south, there had been plenty of cat-like animals on the northern continent before. True, they had not literally been cats, but rather nimravids, a group of remarkably cat-like animals that lived long before actual cats existed. The climatic changes of the Early Miocene seem not have suited them, however, and almost died out as the new epoch dawned. It's possible that one, Dinictis, a bobcat-sized sabretooth, did manage to struggle on for a few million years, but even that is debatable. But, otherwise, while their relatives, the barbourofelids, continued on in Europe, to eventually be replaced by actual cats, in North America... there was nothing.

The Spikiness of Tenrecs

Being a small mammal (or, indeed, any other kind of animal) can be tough; there's always something out there that wants to try and eat you. There are a whole host of adaptations that animals use to try and avoid this fate. Running fast and being good at hiding or camouflage are, perhaps, the most obvious and widespread defensive methods. Another approach is to live somewhere that it's really difficult for most predators to find you, such as spending your entire life in an underground burrow.

Fighting back, as larger horned animals might do, generally isn't so effective, although skunks (for example) have certainly found a way of doing that. But there is also the option of body armour. It's something we see quite a lot in reptiles and, in living mammals, it's perhaps best developed in armadillos. But body armour doesn't have to be a bony or keratinous shell, for something that wants to avoid being eaten, spines can also be an effective deterrent.

On the Origin of Ducks

Presbyornis

This is the post that will be current as of 1st April, when Synapsida traditionally hands over to the Lords of Misrule. Or, failing that, birds.

The fossil history of birds is less well-studied than that of mammals. This is hardly to say that it has been ignored, and we do know a reasonable amount about it. But a key problem with bird fossils is that, in order to fly, birds have light and fragile bones. These don't tend to survive the fossilisation process intact (bats don't do much better) and birds also lack the great standby of palaeontologists specialising in mammals - teeth.

Of course, a notable exception to this are the flightless birds, which can be enormous, and tend to have reasonably solid bones even when they aren't. It's a lot easier to find a reasonably intact skeleton of a terror bird, or even a penguin or fossil ostrich, than it is of something that flies. There's a reason that the previous posts in this April series have all focussed on the flightless sort.

But most birds do fly and are, let's be honest, well known for it. And, despite the difficulties, we do have a number of fossils of flying birds of various kinds - all the way back to Archaeopteryx - so that their evolutionary history is very far from being a blank book.

Small British Mammals: The Smallest Mice

The smallest species of mouse native to Britain, and, indeed, one of the smallest species of mice anywhere in the world, is the harvest mouse (Micromys minutus). With a typical adult weight of around 7 grams (0.25 oz.) or so, it's only around a quarter of the weight of a typical house mouse, and is known by terms translating as "dwarf mouse" in a number of European languages, including both German and Greek.

Harvest mice are widespread, being found across much of Europe, and in a band across Asia that reaches as far as Japan and Taiwan in the east. A 2009 study from Vietnam suggested that the harvest mice there might be a separate species, but it was small scale and not yet fully accepted. Certainly, it's an unusually hot climate for harvest mice which, in Europe, are found only in northern Spain and Italy, only sporadically in Greece, and not in Portugal at all. On the other hand, while they are reasonably common in central and southern Finland and southern Scotland, they are rare in Sweden and absent from Norway. (They also don't reach Ireland, but the sea is the likely barrier there, rather than the climate).

The Beaches of Bakersfield

Modern walrus skull

Seals have a moderately long fossil history, with some of the oldest examples dating from Europe, around 15 million years ago. Although they are now found worldwide, back in those early times, they seem only to have lived in the North Atlantic, reaching the Pacific only around 11 million years ago (probably by the simple expedient of swimming through the seas that then covered what is now Central America).

However, one of the world's best fossil sites for recovering fossil aquatic mammals is at Sharktooth Hill, just outside of Bakersfield, California. Part of the larger Temblor Formation, the deposits here consist of silts and sands, laid down just over 15 million years ago, when California was sweltering in the Middle Miocene Climatic Optimum, a time of unusually high worldwide temperatures - and correspondingly high sea levels. This was before seals had reached so far west, but that does not mean that a number of similar animals did not already live there at the time.

Breeding Cats in Captivity

The Sumatran tiger is a critically endangered subspecies

Although the actual number may be higher, depending on the status of certain subspecies, there are 38 widely recognised species of wild cat. Of these, five are formally considered to be "endangered species", and a further thirteen are "threatened", but not sufficiently so to fall into the riskier bracket. Taken together, that's almost half of the total species, and it ignores the significant number of species that are threatened in parts of their natural range, but survive well enough somewhere else.

The primary reasons for this are habitat loss and poaching, and virtually every species of cat - even those, such as the puma/cougar/mountain lion, that aren't threatened overall - has a declining population. Fortunately, the same thing that makes wild cats attractive to poachers - their undeniable charisma and beauty - also inspires conservation efforts of the sort that, say, the Ethiopian amphibious rat (Nilopegamys plumbeus) could only dream of.

Fluorescent Pink Squirrels

In visible light...

I don't normally cover stories that have been in the news recently, but this was too good to pass up, and, anyway, it wasn't that prominent so some people may have missed it. Fluorescent pink squirrels, oh yeah!

Our story begins in May 2017 with, of all things, a professor of forestry. He was conducting a preliminary survey of the plants and lichens growing in a forest in northern Wisconsin, Many kinds of lichen, and some flowers, fluoresce under UV light, so one way of finding them is to wander around in a forest at night, carrying a UV flashlight. So far, so perfectly normal for the people who study this sort of thing. But, on this occasion, the researcher discovered something entirely unexpected: when he directed his flashlight at a nearby squirrel, it fluoresced a brilliant pink.

This is not something one generally expects squirrels to do. Clearly, more research was called for.

Small British Mammals: Field Mice

Wood mouse

While the common house mouse is likely one of the most familiar of all animals living wild in Britain, it is only one of four species of mouse native to the islands. (France and Germany, for comparison, have six each, although they aren't the same six). Of the other three, the closest relatives of the house mouse are the two species of field mouse, which are also found widely on continental Europe.

Field mice have benefited less from the presence of humans than house mice, since they tend to avoid human dwellings, and there are rather a lot of those in Europe. Given their common name, however, one might suppose that they have at least benefited from the spread of agricultural land. This, however, only true of one of the British species. This is the wood mouse (Apodemus sylvaticus), sometimes also known as the "long-tailed field mouse". In Britain, when the term "field mouse" is used without qualification, it typically means this one.

Miocene (Pt 12): American Rhinos and Horse-Headed Lopers

Moropus

The warming climate of Early Miocene North America was host to a variety of animals, both familiar and unfamiliar. Even in the former category, some of the creatures would have looked a little odd too modern eyes, but we can still say that a three-toed horse is, at least in general terms, still a horse. One group of animals that would be a little harder to place were the oreodonts (or, more technically, "merycoidodontids"), which were already fairly diverse when the Miocene dawned.

These creatures were unique to the continent and were medium-sized herbivores. They would have looked vaguely like pigs, although without the flattened nose-disc of those animals, and with four functional toes on each foot. As far as we can tell from their teeth, they were mostly browsing animals and were spread quite widely across the continent.

Land Mines and Scent Marks

For primates such as humans, vision is our primary sense. For the majority of mammal species, however, the most important sense is probably that of smell. In addition to using this sense to scope out the natural environment around them, many mammals leave scent marks as messages to one another, marking out a territory, advertising their willingness to mate, or whatever else they wish to convey.

Much research on the nature of scent marking focuses on how and where the animal leaves these messages, or how they may differ based on sex, maturity, and so on. This is obviously important if we want to understand why they're doing it, and what it is that they're trying to 'say'. But, naturally, it's also useful to understand how other animals of the same species respond to those marks - there's no point leaving a message if everyone else is just going to ignore it.

The Hybrids are Coming

Hybrid domestic pig x wild boar

Conservation - whether it be of mammals or any other kind of animal or plant - tends to focus on the species level. These are the discrete kinds of living creature that can be most easily identified and preserved, ensuring that the mix and variety of the natural world remains as close to its original state as possible. Preservation of subspecies is often a lower priority, which makes sense if you really have to make the choice, but it, too, can be important if we want to preserve such things as genetic variation within a species.

The common understanding of a 'species' is that it consists of a group of animals that cannot interbreed with animals outside that species to create fertile offspring. This, however, is an oversimplification; lines blur, and not always in neat and tidy ways. Scientifically, there are multiple different ways of defining what a 'species' is, but the general idea is that it has to be a group of animals that can be readily identified as different from their relatives. Which tends to mean that, even if they can interbreed with other species, they generally don't, at least in the wild, and maintain a separate gene pool.

Small British Mammals: House Mice

Over the last few years, I have done a roughly annual series covering particular groups of mammals, exploring all the different species, familiar and unfamiliar, that belong to them. (If you haven't read the past ones, the link "Synapsida Series" points to the list of them; note that the individual posts appear in reverse chronological order once you select a series to view). One problem with selecting which groups to cover in a given year is that only some groups will really work, and, even then, some are clearly better than others.

One problem, for example, is that some groups are simply too large, and if you split them down into narrower groups that are more easily handled, there's no longer enough variety for it to be worth it. Such is particularly true of small mammals. There are over 700 species in the mouse family, for instance, with over 500 of those in the "murine" subfamily, which includes all of the familiar ones. Even if it would be practical to describe them all, most of the individual species haven't been studied in any detail, so you'd rapidly get a long list of "looks mouse-like, lives in XX".

Murderous Whales of the Eocene Oceans

The relationships between what animals eat can be thought of as a pyramid. At the bottom are plants, which are eaten by herbivores, which are eaten by carnivores, which are eaten by larger carnivores. The reality is much more complex, and is more accurately thought of as a web (omnivores exist, large carnivores also eat herbivores, etc.), but the general principle is broadly true. In particular, the further up the ladder you go, the fewer animals there are, since the transfer of energy from one level to the next can never be 100% perfect.

At the top of the pyramid are the "apex predators". These are the carnivores that have no predators of their own, that are able to feed without fear of being eaten themselves. Again, the reality is more complex - an adult of one apex predator might occasionally kill and eat the young of a different kind, for instance. And, of course, everything gets eaten by worms (or whatever) once they're dead. Nonetheless, really big scary predators clearly do exist, even if, by their nature, they aren't very common.

Requiem for a Dolphin

Dolphins are social animals, living in pods and engaging in what seems to be fairly sophisticated communication. It's likely that such behaviour is part of the reason for their success, with well over 30 species spread across the world's oceans... and that's excluding porpoises, and some other "dolphin-like" animals outside the dolphin family proper.

Sociability involves a number of different traits and behaviours, but one that's known to exist in cetaceans and relatively little else, other than primates, is what's technically known as epimeletic behaviour. This is, in essence, the act of helping other members of your species when they are in trouble, typically due to an injury of some kind. (For what it's worth, this compares with etepimeletic behaviour, which is acting in such a way as to make it easier for others to care for you).

Gerbil versus Rattlesnake

Sidewinder

Deserts are harsh environments, and living in them poses animals a number of problems, not least of which are daytime heat and an absence of water. In order to survive in such a place, animals need to evolve suitable adaptations - extremely efficient kidneys to reduce water loss are one such example.

But the thing about deserts is that, while there are some geographic differences between them, the challenges of living in one are at least broadly similar regardless of which desert it happens to be. And while, say, the world's seas are all connected, the deserts aren't. So animals, including mammals, have had to evolve means of surviving in them several times over, re-developing the necessary features each time they encounter a new one.