Prehistoric Mammal Discoveries of 2018

Gordodon,
a new non-mammalian synapsid described this year

And so another year approaches its conclusion. As usual, I will wrap up here with a post looking at things from a slightly wider perspective. This time around, as I did last year, I am going to take a brief look at a range of scientific papers on fossil mammals that were published in 2018. There's not going to be any particular theme here beyond that, merely a list of things that caught my interest, and that were not, for various reasons, included in the blog proper. So, here we go:

Beginnings and Endings

In the modern day, it's pretty easy to tell mammals and reptiles apart. But, if we go far enough back in time, that eventually ceases to be so true. A common misunderstanding is that mammals evolved 'from' reptiles, but, in reality, mammals and reptiles are separate evolutionary lines that have lived alongside one another since long before there were dinosaurs. At least, that's true if we use the modern definition of 'reptile' since, of course, the animals that mammals really did evolve from would have looked an awful lot like reptiles if we'd been able to see them in the flesh.

Miocene (Pt 11): Horses on the Grasslands

Daeodon

The lush greenery of Early Miocene North America was a good place for large mammalian herbivores. Many of these, such as musk deer, pronghorns and camels, were, in one fashion or another, cud-chewing animals, able to extract maximum nutrition from a grassy or leafy diet. But many, of course, were not, either finding different ways to get the most out of their food, or else going for plants that were generally easier to digest.

Some of these were, like the ruminants, cloven-hoofed animals. Today, the main group of non-ruminant cloven-hoofed animals are the pigs, but they have never truly lived wild in the Americas, with feral 'razorbacks' only having arrived with the white man. Instead, America has peccaries, also known as javelinas, animals that look very much like pigs, but have a number of crucial differences.

Not the Pig Family: Fossil Peccaries and More

Mylohyus

Today, there are only three recognised living species of peccary, the smallish pig-like animals that inhabit the Americas... and one of those is endangered. However, these are but the last remnants of a once much larger group with a fossil history that stretches back even further than that of the true pigs.

While pigs date back, at the best, to the end of the Oligocene epoch, the oldest known peccary fossil dates from the end of the epoch before that, the Eocene. This implies that the ancestors of the peccaries entered North America from Asia between 36 and 34 million years ago. The fossil in question belongs to a species known as Perchoerus minor, and it's also worth noting that it is also the smallest peccary known... in fact, it was about the size of a typical house cat.

Twilight of the Almost-Primates

The primates are one of the major groups within placental mammals, currently considered to contain at least fourteen different living 'families', and probably more. Given this, and the fact that they are fairly distinctive, it's not surprising to discover that they are also a very ancient group. Genetic studies, back by estimates of how frequently mutations ought to occur, imply that they may date all the way back to the extinction of the dinosaurs, or at least its immediate aftermath.

The oldest undisputed fossil primate we currently know of isn't quite that old, however, and dates back 'only' 55 million years to the dawn of the Eocene epoch. I have to add the word 'undisputed' to that, though, because it wasn't alone - a number of other very primate-like animals did live at the same time, and, indeed, somewhat earlier.

These animals are collectively called 'plesiadapiforms', and it would be fair to say that there is still some considerable debate as to what they actually were. Just as with the question as to how many families of living primate there are, this depends not on how the different groups are related, but on where we choose to draw the lines between them. In the case of living families, the question is whether we consider marmosets and night monkeys to belong to the broader capuchin family, or whether we consider them different enough to count as families in their own right. In the case of the plesiadapiforms, it's whether they're really weird early primates, or whether we consider them to be merely close relatives.

How Baby Bats Learn to Fly

Small mammals, on the whole, live fast and die young; a great many of them live for only a single year. And that's assuming they don't get eaten first, which, unsurprisingly, they often are. In order to maintain their numbers, then, it is essential that they breed early and often. In particular, they tend to have large litters, which they then need to get to adult independence as quickly as possible. The common house mouse, for example, can breed at least five times a year, and gives births to litters of typically around five to eight pups at a time, each of which is sexually mature within less than two months.

This is not, however, what we see with bats.

The Grunting of Baboons

Olive baboon

While they also often have other means at their disposal, mammal species typically communicate with one another through sound. For those that live solitary lives, this tends to be fairly unsophisticated, beyond, perhaps, the need to attract and woo a mate. For social animals, sound production can, however, be more complicated, allowing the sort of short-term immediate communication for which scent-marking is not appropriate.

An obvious example are alarm calls, in which one member of a herd or other group will alert its fellows of a predator or other threat. Another are the distressed 'separation calls' that young mammals use when they can' find their mother. And then, of course, there are mating calls, or aggressive roars and the like intended to intimidate a rival.

But there are also peaceful, non-sexual, contact calls whose primary intent appears to be simply maintaining the cohesion of the group. For example, meerkats regularly use calls to decide when to move on to new foraging grounds, keeping the group together using the principle that if three or more members 'vote' to move by making the appropriate call, then everybody moves at once. African elephants can even use long-distance communication to maintain social bonds with individuals that may be literally miles away.

The Pig Family: Fossil Pigs

Kubanochoerus, the unicorn-pig

There are seventeen widely accepted species of pig alive today. Although some, notably the wild boar and the two kinds of warthog, are doing absolutely fine in the grand scheme of things, many are threatened to varying extents by hunting and loss of habitat. Three - the pygmy hog and the Visayan and Javan warty pigs - are formally listed as endangered species by the IUCN, and many of the others are just outside that category. On the bright side, no clearly identified species of pig has actually slipped over the line into extinction in the last few thousand years. But, of course, if you go back a few million years, it's a rather different story.

Indeed, in some respects, the pig family as it exists today is a shadow of its former self. Pigs have always been reasonably successful animals (at least, without human interference), given their adaptability, moderate intelligence, and willingness to eat just about anything. But, in the past, they were more varied than today. In total, there are five generally recognised subfamilies within the overarching pig family - and all but one of them are known only from fossils.

Miocene (Pt 10): The Beasts with Three Horns

Syndyoceras

At the dawn of the Miocene, 23 million years ago, North America was, in many respects, quite different from the way it is today. It was, at the time, separated from South America by a wide expanse of sea, and, perhaps more significantly, the Sierra Nevada and Cascade Mountain ranges, which today run from southern British Columbia down into Mexico, did not yet exist as any more than a series of particularly high hills. While the Rockies were already mountainous, so that there was at least some rain shadow, in general, the continent was wetter and more forested than today, lacking the great grassy prairies that are so dominant today.

As the climate warmed, sea levels rose, flooding low-lying coastal regions and turning major valleys into bays. For much of the epoch, for instance, Florida was almost entirely underwater. Further north, however, it was still connected to Asia (and Greenland, although that's less significant in the grand scheme of things). Perhaps because the land bridge was both far to the north and relatively mountainous, not many animals seem to have crossed it, but that changed in the Early Miocene as the climate began to improve, and only increased as the epoch wore on. And, for whatever reason, most of them were heading east - into America.

The Best Time for Breeding

Animals, as a rule, want to give birth when their offspring have the best chance of survival. In particular, it's useful to give birth at a time when suitable food is most abundant, whether it's to allow the mother to produce enough milk, or to wean the growing young onto solids more quickly. If the animal in question is short-lived, the time of year may not matter too much, so long as the mother is well-fed and in good physical condition. If you have to breed multiple times each year, you'd better get on with it.

It may also not matter too much if the animal lives somewhere where the seasons don't change too much, although, even in the tropics, where there's no winter, there's usually a rainy and a dry season. A great many mammals, however, do have a specific breeding season, timed to be one gestation-length away from the best time to give birth. If pregnancy lasts six months, and the best time to give birth is in the spring, when fresh plants are sprouting, you'd better do your mating in the autumn. If pregnancy lasts twelve months, however, you want to mate in the spring. And so on.

Bats That Eat Fish

Greater bulldog bat

With over 1,300 different species of bat known, it shouldn't really be surprising that there's a wide range of different dietary habits among them. Of course, a lot of that is on a fine scale, as I discussed just last month, but there are more significant differences in the kinds of things that bats feed upon. Insects, fruit, nectar, even blood all form the core diet of at least some kinds of bat.

One of the more unlikey food sources, however, is fish. Yet, when you think about it, fish is a really common food source for birds - there are a huge number of bird species that feed primarily on fish, including seagulls, kingfishers, and ospreys, among many others. Clearly, there's no inherent reason why a flying mammal couldn't eat fish, yet very few of them do.

As a recent review makes clear, however, "very few" is not "none".

Not the Pig Family: Peccaries of the World

Collared peccary

I've already described the anatomical and biological differences which mean that, despite appearances to the contrary, peccaries are not pigs. I've also described all the various living species of the pig family, which means that it's now time to do the same for the living species of the peccary family.

The peccary family is, however, a lot smaller than the pig family: it contains just three living species.

The one that's likely most familiar to readers of this blog is also the most widespread: the collared peccary (Pecari tajacu). It's so-named because of the thin 'collar' of whitish hair that runs from its shoulders across the throat, although, in practice, this isn't always as visible as it might be. The animal is found through pretty much the whole of central and northern South America east of the Andes, through most of Central America, coastal (but not central) regions of Mexico, and into neighbouring parts of the USA, where it can be seen in Arizona, New Mexico, and Texas. If a distinction is needed, this is the true "javelina", since it's the one that's common where that alternative word for "peccary" is most commonly used.

Lions in the Carpathians

When I last talked about Eurasian cave lions, back in 2013, I said that there was some debate as to whether they were a distinct species, or just an unusual subspecies of the modern, living, lion. Although the issue is, perhaps, still not entirely resolved, it's probably fair to say that the clear majority opinion these days is that they were a separate species (Panthera spelaea).

This swing in opinion has been helped by new genetic data, something that we can obtain because the animals died out so recently - around 12,000 BC by most estimates. Specifically, an analysis published in 2016 was able to obtain the full mitochondrial genome of a pair of cave lions, allowing a more detailed genetic analysis than ever before. This showed that, as expected based on earlier studies, cave lions really were "lions" in the sense that they were more closely related to modern lions than thy were to, say, leopards.

The Hunting Grounds of Small Cats

The big cats - lions, tigers, leopards, and so on - are arguably amongst the well-known of all wild animals. They frequently figure in zoos and nature documentaries, and, from the scientific perspective, they have been the subject of numerous studies down the years. Even the medium-sized cats, such as lynxes, bobcats, and ocelots, are well known, and, at least in the case of the European and North American species, also well-studied.

We know somewhat less about the assorted species of genuinely small cat - the ones that are about the size of the typical domestic moggy. Yet there are an awful lot of them, even if most members of the public would likely have a hard time naming more than one or two.

One such example is Geoffroy's cat (Leopardus geoffroyi) named for - though not discovered by - the pioneering French naturalist Étienne Geoffroy St Hilaire. This lives in southern South America, reaching Bolivia, Paraguay, and the southern tip of Brazil in the north, and also found just over the border in Chile, but mainly inhabiting Argentina and Uruguay. While they prefer terrain with scattered trees and plenty of bushes, the also live in open grassland, and are found right down to the very southern coast of South America, although not on the islands beyond.

Modified Munchies of Many Mouse-eared Myotises

In the modern system of taxonomy for the classification of living things, a genus is  group of closely related species. It is the lowest mandatory level of classification, apart from 'species' itself, and forms the first half of a creature's scientific name. Thus, Panthera, for example, is the genus containing lions, tigers, leopards, snow leopards, and jaguars.

As such, we'd typically expect a genus to contain only a small number of species - it is, after all, the smallest standard grouping of species that there is. And, at least for mammals, this is typically the case. Many genera, in fact, have only one known species, or at least only one that isn't extinct (as is the case for our own genus, Homo, for example). But there are some exceptions, cases where there are so many incredibly similar species that we just have to lump them all together.

The single largest mammal genus, as commonly defined today, is Crocidura, which represents nearly half of every species of shrew we know about. But even the second largest, Myotis, is a whopper.

The Pig Family: Peccaries Are Not Pigs

Over the the year so far, this series has described every living species of pig. Yet there are some animals that might seem to be missing. Found across much of Latin America, and up into the southwestern USA, we can find animals known as peccaries. These certainly look like pigs, and, unlike razorbacks, which can also be found in the US, they are genuinely wild animals, not the descendants of domesticated ones that happen to have escaped.

The reason I haven't mentioned them so far is, as the title of the post makes apparent, that they aren't actually pigs. So why the heck not, and what are they, if they're not pigs?

400th Synapsida

With this being the 400th post at Synapsida, it is once again time for my biennial piece of navel-gazing, in which I see what has happened over the last 100 posts, and where I might be going next.

There's no change to the most frequently used tags over the last 100 posts, with evolution and behaviour topping the list, as might be expected, given the general theme of the blog. (I'm ignoring tags directly related to particular 'series' here, of course). Bubbling under are topics related to diet, sociability, and reproduction. Given some of the animals I have been looking at, it is unsurprising - if rather depressing - that endangered species are also mentioned quite frequently.

Miocene (Pt 9): The First Sabretooths in Europe

Amphimachairodus

When hyenas first evolved, they were small, tree-dwelling animals, searching for rodents, birds, and the occasional insect among the branches. By the Late Miocene, they had already begun to come down from the trees, but many were still small, and resembled a mongoose more than a modern hyena. A few, such as Thalissictis, were larger, an early step on the path to the more familiar forms of today.

During the early part of the Late Miocene in Europe, however, the older forms still dominated, evidently showing that their lifestyle was still a valid one, perhaps in part because they weren't directly competing with their more "modern" looking relatives. Nonetheless, as the Late Miocene dawned, newer species of hyena began to appear, and these had a more dog-like appearance than their relatives. As a result, it has been estimated that as many as 20 different species of hyena may have lived in Eurasia at the time, with a greater diversity than today.

Rabbit v. Rabbit

Mountain cottontail

There are literally thousands of different mammal species currently recognised. Most of them are small, and a great many of them can be quite hard to tell apart at first glance. Or even second glance, quite frankly.

The reason that they look so similar is that some body plans have been particularly effective, allowing the creatures possessing them to survive and multiply across the globe. But, if they're so similar, why doesn't one species, over the course of time, drive the other to extinction? Even if one isn't even just marginally better at doing whatever it does than the other (and, since they aren't literally identical, that's unlikely) then sheer bad luck ought to hit one or the other of them eventually.

The Pig Family: The Strange Case of the Sulawesi Pig-Deer

Sulawesi babirusa

Warthogs are fairly odd-looking animals, as are forest hogs, among others. But, at least to my mind, when it comes to wild pigs, nothing quite beats the babirusas.

These strange looking pigs inhabit the island of Sulawesi in Indonesia. Unlike most of the others in the group, this has been an island for far longer than pigs have been in existence - when sea levels were lower, most islands to the west were joined with Asia, and those to the east with Australia, but the waters around Sulawesi are so deep that it remained isolated. I've mentioned this before, in the context of warty pigs, so it's interesting to note that those channels must have been crossed by wild pigs on no less than three occasions (the third sort of Sulawesian pig, Celebochoerus, died out in the Ice Ages).

False Deer-Llamas of Bolivia

Theosodon
(the nasal bones are that 'bump' on the forehead
just forward of the eyes)

Australia is an island continent, separated from the rest of the world's landmass for millions of years, allowing it to develop its own unique wildlife, from kangaroos and wombats to bandicoots and emus. The only other island continent we have today is Antarctica, which has no native land mammals at all (or emus, obviously).

In geological terms, however, South America was also an island continent until relatively recently, only joining North America three million years ago, towards the end of the Pliocene epoch. Even today, the strip of land connecting the two is only 35 miles (60 km) or so wide at the narrowest point, both narrower and longer than that connecting Eurasia to Africa. This means that, like Australia, South America had a long history of so-called "splendid isolation", and it evolved a number of unique animals in the process.

Monkeys, Apes, and Simians

Is this an ape or a monkey? Or both?
(Answer at the bottom)

There is, it seems to me, quite a lot of confusion among the general public about the term "monkey", and exactly which species of animal it might cover. Some people refer to chimpanzees as monkeys, while others reserve it for animals with tails, such as macaques and spider monkeys. And what about baboons or gibbons? Come to that, aren't there other kinds of primate? Where do they fit in?

Or us? Are we monkeys? Are we descended from monkeys? Or neither?

In short, what precisely is a "monkey" in scientific terms? About three-and-a-half years ago, I blogged about the definition of "primate", so perhaps now I'll look at some broad types of primate, and how they fit together.

The Pig Family: Warthogs

Common warthog

Warthogs are, quite possibly, the best known species of wild pig after the wild boar itself. They are relatively common animals, readily observed in the habitats where they live (rather than hiding in dense thickets, say) and, perhaps above all, they have a striking and distinctive appearance.

The common warthog (Phacochoerus africanus) is widespread across sub-Saharan Africa, and is currently thought to have four different subspecies. Unlike other African hogs, they inhabit lush grasslands and open savanna, country dotted with trees and waterways, but neither densely forested nor the truly arid terrain of veldt or desert. Two subspecies live in the north, in the Sahel belt that separates the Congo rainforest from the Sahara, and are found right from the Atlantic coast of Mauritania to the shores of the Red Sea in Eritrea. The others are found across East Africa and pretty much the entire south of the continent outside the deserts, reaching as far as South Africa.

Miocene (Pt 8): Giant Honey Badgers and European Pandas

Indarctos

A great many predators lived in Europe in the glorious warmth of the Mid Miocene, when the continent was lush with subtropical vegetation and the herbivores that fed on it. As the climate began to turn, and the forests gave way to more open terrain, both the herbivores and the animals that preyed on them underwent a number of changes, with the latter in particular suffering some loss of diversity. (At least, so far as we can tell from the incomplete fossil record).

This affected the full gamut of mammalian carnivores, including many of the smaller, less obvious, ones. The boundary between the Middle and Late Miocene is an arbitrary one that isn't really marked by anything much in Europe, so that, to begin with, these were as numerous as ever. There were badgers, such as Sabadellictis, and even skunks, which today are not found outside the Americas.

Fishing in the Ganges

The most spectacular cetaceans are, arguably, the really big ones - sperm whales, blue whales, and so on. However, while our knowledge of the exact numbers is a little hazy, somewhere around half of the cetacean species alive today represent much smaller animals. The majority of these belong to just two taxonomic families.

By far the most numerous are the "true" or "oceanic" dolphins, a family that also includes killer whales and pilot whales - small in comparison with the like of humpbacks, but fairly large by most standards. The second family are the porpoises, which are exclusively small, by cetacean standards, and usually slightly smaller than dolphins.

But there are a few small-sized cetacean species that fall into neither group. These oddities share one thing in common: they don't live in the sea. While they are, of course, just as fully aquatic as their better-known kin, this has lead to them receiving the common collective name of "river dolphin", thus distinguishing them from the "oceanic" sort that most people are more familiar with.

What is a Marsupial?

A possum

In America, the word "possum" is usually used to describe a moderately-sized, somewhat rat-like, animal that has grey fur, sometimes pretends to be dead, and has far too many teeth for any self-respecting land-based mammal. Officially, this creature is an "opossum", and more specifically, the Virginia opossum (Didelphis virginiana). The word comes from the language of the Powhatan people of Virginia, and has been in use in English since at least the 17th century.

Over on the other side of the world, in Australia, the word "possum" is, however, used to refer to an entirely different animal. These are nocturnal, tree-dwelling creatures, typically with large eyes and long tails, and the majority of the seventy or so species are herbivorous. Early settlers, who had probably only vaguely heard of the American animal, nonetheless decided to give it the same name. Like the Americans, over time they confused "opossum" with "a possum", and shortened the word. Unlike the Americans, their shortened word became not merely colloquial, but the one formally used in zoological texts.

The Pig Family: Bush Pig, Bushpig, Red River Hog

Red river hog (boar)

As zoological knowledge has advanced, the number of species that we know about has changed regularly, and not just because we keep discovering new ones. Animals that we knew about, but previously thought were subspecies get promoted to full species, and animals that we thought were separate species turn out not to be.

In fact, over time, we can sense something of a trend here. Beginning with Linnaeus in 1758, several new species are named, often by naturalists unaware, in the days before fully up-to-date reference libraries, let alone the internet, that somebody else had already given a name to the same thing. That process continues through the 19th century, with minor differences being seized on as evidence of speciation, even where it was possible to make decent comparisons. Through the 20th century, the number of genuinely new species being discovered dramatically tails off (at least, for mammals), but there's also a tendency to tidy up the great mass of inherited names from the past, merging similar animals together. Finally, from the late 20th century onwards, an increasing understanding of genetics results in numerous subspecies being promoted, often with our Victorian predecessors turning out to have been right all along.

The Fast Lives of Early Sperm Whales

Livyatan melvillei, a Miocene species
(It was supposed to be 'Leviathan', but the name was
already taken)

Sperm whales are magnificent and highly distinctive animals. While they may not be quite as large as the great toothless whales, they are still pretty huge: a fully grown male is typically about 16 metres (52 feet) in length and weighs over 40 tons. So distinctive is it, in fact, that today it is usually considered to be the only living species in its family, the Physeteridae.

The caveats in that last sentence - "today", "usually", and "living" - are all significant. On the first two points, the sperm whale family used to be considered to contain no less than three living species, and some researchers still define it that way. The other two species are the dwarf and pygmy sperm whales (Kogia spp.), and they're typically (but not always) placed in their own family these days. As their names suggest they are much, much smaller than the "true" sperm whales, being more like the size of a large dolphin.

Broken Bones and Missing Toes

Woodland jumping mouse

Life can be hard, especially out in the wild. Injuries can be common, and among the most painful are broken bones. As humans, we can mitigate bone fractures using splints, braces and so on, but wild animals have no such luxury. Nonetheless, bones do heal by themselves, a process that starts with the formation of a tough fibrous scar at the injury site that at least helps to keep things fixed partially in place. Over time, the scar is mineralised to form weak, but functional, bony material, and then eventually rebuilt with as much of the original structural integrity as possible.

Without splints and braces, this is likely to be an imperfect fix, even assuming that the injury doesn't prevent the animal from feeding or otherwise kill it before the process completes. If the animal does survive, the signs of the injury are always going to be there in its skeleton, and are quite likely to cause at least some ongoing problems. But, survive they do, and bone healing wouldn't have evolved in the first place if it never worked in the wild.

The Laziness of Venomous Shrews

While there are some bats that could challenge them for the title, by most measures, shrews are the smallest of all mammalian species. They typically weigh no more than about 20 grams (two-thirds of an ounce), and are often much smaller than that. Being so small poses a number of challenges, but there's one in particular that affects mammals of this size that would not affect, say, beetles.

This is because mammals are warm-blooded, and need to generate internal heat in order to keep functioning (unless they're hibernating). The smaller you are, however, the more rapidly you lose heat through your body surface, which means that shrews need a fierce metabolism to keep burning enough calories to keep themselves warm. This means that they have to eat almost constantly, but it also means that they want to exert themselves as little as possible while doing so, so as to waste the minimum amount of energy in the process.

The Pig Family: The World's Largest and Smallest Pigs

Pygmy hog

By some definitions, the term "pig" can really only be applied to those species that are most closely related to the domestic animal; those included within the genus Sus. This includes the wild boar, and the various kinds of warty and bearded pig that inhabit the Indonesian and Philippine islands.

But these are not the only pig-like animals to inhabit Asia. In 1847, Brian Hodgson, a naturalist and former colonial administrator who was living in Darjeeling at the time, described and named the pygmy hog (Porcula salvania), an animal he considered so different from regular pigs in the shape of its teeth and feet that he placed it in its own, newly defined, genus, Porcula. (The scientific name, incidentally, translates as "piglet from the Sal Van", the latter being a forest that only coincidentally sounds like the Latin "silvae" meaning "woodland").

Miocene (Pt 7): Hornless Rhinos, Long-Tusked Elephants, and Three-toed Horses

Anancus arvernensis

As the climate cooled around 11 million years ago, the forests of Europe began to thin out once more, something that favoured fast-running animals such as horses. Until this time, the only kind of horse in Europe, however, was the small, three-toed, Anchitherium, which was likely adapted to dense woodland and not so suited to the new climate. Its own ancestors had reached the continent from the east, having crossed over during one of the periodic rises of the Bering Land Bridge, but now, not coincidentally, given the colder climate, the Land Bridge rose again, and a second kind of horse followed it out of the Americas.

Diving for Your Dinner

Dinner!

Cetaceans (whales, dolphins, and porpoises) are the best adapted of all mammals to life underwater. Their food is often found far below the waves, requiring them to dive deep to find it. But this, of course, is countered by the fact that, not being fish, they also have to return to the surface to breathe. The deeper the desirable food happens to be, the longer they will have to dive for just to reach it, and the longer they will have to spend recovering on the surface afterwards - even if the actual feeding time remains the same.

Such pay-offs are arguably particularly important for the huge rorqual whales, which feed by lunging at great masses of krill or other small prey and gulping them down. For them, it really matters that wherever they are diving is rich in food, so that they can find enough to offset the effort required to catch it. Quite how they strike that balance should depend on how good they are at diving, which relates to things such as their lung capacity and how much oxygen they need to sustain their bodies.

Out of the Caves

At least if you live in the northern, temperate, parts of the world, when you think of where to find bats, your first thought is likely to be "caves". A great number of bat species do, indeed, spend the day in caves, and this makes sense: if you're a nocturnal animal that doesn't need light to 'see', then caves are both reasonably safe places and ones with a constant, sheltered environment. Why bother trying to sleep in the wind and the rain, or even the bright sunshine, when you don't have to?

But, of course, by no means all bats are cave-dwellers. Amongst the various families of bat, the leaf-nosed bats (Phyllostomidae) of the American tropics are the most varied in terms of diet, and also in terms of their roosting habits and other behaviour. Sure, the majority of phyllostomid species do eat insects and live in caves, as most other bats do. But the group also includes some bats that feed on surprisingly large prey (such as birds) as well as the blood-drinking vampire bats.

It also includes a large number of species that are vegetarian, feeding on fruit such as figs, or subsisting almost entirely on the sugar-rich nectar that they drink from year-round tropical flowers. Many of these fruit-eating species do not live in caves at all, but simply roost in trees - as do the much larger fruit bats of the Old World

The Pig Family: Threatened Pigs of the Philippines

Visayan warty pig (female)

When the animal we now know as the Sulawesi warty pig was first described, back in the 19th century, it was thought that it lived, not only on the island of Sulawesi, but also on a whole chain of islands to the north - the Philippines. But the pigs there didn't look exactly the same as those to the south, so in 1886, German zoologist Alfred Nehring proposed that they be regarded as a distinct subspecies.

And so things remained for a hundred years, until scientists began to look more closely at the animal's genetics. When they did so, they discovered something fairly surprising. Pigs typically have 38 chromosomes (compared with 48 in humans), but it turned out that the warty pigs from the Philippines had only 36 - an entire pair had disappeared, its genetic material shuffled around elsewhere in the genome.

The Curious Necks of Giant Rodents

Josephoartigasia

We tend to think of rodents as small mammals, and the great majority of them are: mice, voles, hamsters, tree squirrels, and so on. Even rats and gophers aren't really all that big. Indeed, when most people think of rodents they probably aren't mentally including the largest ones, such as porcupines and beavers. In fact, the very largest rodent alive today is the capybara, a sort of giant guinea pig that is around 120 cm (4 feet) long and weighs something like 50 kg (110 lbs).

This, you probably won't be surprised to learn, is as nothing compared to some of the fossil species.

No Boys Allowed

Even in mammals that are otherwise social, it is quite common for males and females to live apart for most of the year. The most common pattern involves females living in groups with their children, until the latter approach adulthood, while males either live alone, or in much smaller bands, outside of the mating season. In many hoofed herd animals, however, the males live in herds that aren't much smaller than those of the females - in other words, both sexes live in herds, but the two don't mix until it's time to do the necessary.

Clearly, these are creatures that benefit from the group protection that living in herds provides, and, while there's obviously a limit on how large a herd can be before there isn't enough food to support them all, it's not always so clear why the herds should be single-sex. Why, in short, do so many hoofed herd animals practice sexual segregation?

There are a number of theories, and, as is often the case, they aren't mutually exclusive. Nor is it likely that the reason - or the balance of reasons, if there's more than one - will be the same for every species. It's something we have to examine on a case-by-case basis.

First of the Flightless Penguins

Waimanu

Penguins are unusual birds. They walk fully upright, have short legs that force them to waddle, and have wings adapted into flippers to propel them through the water. Compared with many other bird groups, there aren't all that many of them - there are no more than twenty living species, and possibly less, depending on who you talk to.

Surprisingly, perhaps, we have, however, named many more fossil species than living ones, and our understanding of penguin evolution is rather better than that of most families of flying bird - which tend to have light and fragile bones that don't fossilise well. Unfortunately, as is often the way, it's the earliest and most interesting part of that fossil history that's most obscure, since, being older, these are the fossils least likely to be preserved.

But that doesn't mean we have nothing from that time.

The Pig Family: Wild Pigs of Indonesia

Bearded pig

Thanks to their adaptability, wild boar are a remarkably widespread species, being found from Portugal to Japan. All of their close living relatives, however, are much more restricted, each being isolated on different islands or island chains off the south-east coast of Asia.

The largest such island, and, indeed, the third largest island in the world, is Borneo. This is home to the bearded pig (Sus barbatus), which is also found, not only on the neighbouring island of Sumatra, but also on the Malaysian mainland. The Bornean and Sumatran forms of the animal are widely regarded as different subspecies - the latter going by the rather brilliant name of S. b. oi - although quite which of these two the Malaysian pigs belong to has been a matter of mild controversy.

Miocene (Pt 6): The Coming of the Mice

Palaeotragus

The Early and Mid parts of the Miocene epoch were, for the most part, times when the world was much warmer than it is today. It wasn't a steady pattern, however, and I've already described how the fluctuations in climate, over the course of many millions of years, affected the rodents of Europe. It was a time when the most common small mammals in Europe were not mice and voles, but dormice, accompanied by early hamsters, squirrels, and the gliding eomyids.

By 10 million years ago, however, the colder, drier climate had become locked in for the long term. We know that the forests of Europe changed dramatically at this time, the old subtropical trees, such as figs and palms, being replaced by oak, alder, and elm. Likely as a result of this change in the available food supply, most of the dormice died out, leaving only a few close relatives of the relatively small number of species we have today.

The Crusty Forearms of Male Bats

Bats, of course, are not blind. There eyesight is, in fact, pretty good in the majority of species. Which makes sense for an animal that has to fly around at night when the light is dim but not entirely absent. It's only for animals like moles, which live underground, where the light can't penetrate at all, that vision becomes an expensive and unnecessary luxury.

Having said that, many species of bat do spend a lot of time in caves, and, in there it really is too dark to see anything, no matter how good your night vision might be. As a result, the other senses of bats are often highly tuned. Hearing is the obvious one, since bats rely on that for their sonar abilities, but many species also have well-developed senses of smell. In particular, since bats also tend to be highly social, scent often forms a crucial part of their ability to communicate with one another - as it does for many other mammal species.

Silence of the Pacas

Whether or not a given species of animal lives in groups is something of a trade-off. Several different factors are involved, but just one example is that you will simultaneously be more visible to predators and be protected from them by "safety in numbers". For many animals, the benefits outweigh the downsides, although a lot depends on the individual environments and lifestyles of those creatures.

But living in groups also brings its own requirements, perhaps most notably the need to communicate with other members of your herd or pack. Safety in numbers, after all, is of limited utility if one member of the group can't warn others of something dangerous it's just seen. And this isn't simply a yes/no situation; the more complex the group structure, it is argued, the more sophisticated the communication needs to be.

The Pig Family: Wild Boar and the Domestication of Pigs

European wild boar

Generally speaking, the wild ancestors of agricultural animals have not fared particularly well. Wild goats are a threatened species, wild horses are an endangered one, camels are doing even worse, and wild cattle have been extinct for centuries. Wild sheep haven't done quite so badly, although they're hardly widespread, but, in general, one of the main problems facing such animals is that the sort of places they like to live are exactly the ones we want to turn into agricultural land to raise their domesticated kin.

Indeed, only two wild ancestors of widely domesticated herbivore are doing well: chickens and pigs. (This may, of course, depend on your definition of "widely"; I'm ignoring, say, rabbits). Indeed, the wild ancestor of the domestic pig is not only reasonably common, it's the single most widespread of any species of wild pig.

Early Whales of the North Pacific

The majority of living cetacean species belong to a group called the odontocetes, or "toothed whales". Most of them aren't really what we think of as "whales" at all, since the group includes all of the dolphins and porpoises. The group does, however, include a number of much larger species - some of them just really big dolphins, such as the killer whales, but others being less closely related, such as sperm whales, beaked whales, and narwhals.

The odontocetes as a whole stretch back far into the fossil record, with the oldest known examples dating back to around the dawn of the Oligocene epoch 34 million years ago. They rapidly spread across the globe, unhindered by the geographical barriers that often affect more land-based mammals. (The continents were all separate at the time, which would have helped, since it was possible to swim right around the globe without leaving the mid-latitudes).

Jackals on the Motorway

Mammals tend to have a particular area in which they live most of their lives and conduct their various activities. This is known as the animal's "home range", and it's not quite the same thing as a "territory". That's because the latter is an actively defended bit of land, that the animal strives to keep clear of rivals, perhaps marking it with scent as a warning, and using aggression against intruders if they have to. The majority of mammal species don't bother to defend territories, but that doesn't mean that they don't have a home range - after all, they have to live somewhere.

One key difference between a territory and a home range is that the former, by definition, is not shared with any neighbours. Of course, the animal might be social, living in herds, packs or other kinds of band, so that all members of the group share a single territory, but, again, it's not shared with outsiders. A home range, on the other hand, almost always overlaps with at least some others used by members of the same species, especially if they happen to be of the opposite sex. Breeding would be problematic if they didn't.

How Mothers Stop Their Daughters from Sleeping Around

Northern mole-vole (E. talpinus)

Generally speaking, mammals are equally likely to be born as either males or females. The exact proportion may vary a little, and it doesn't follow that both sexes form 50% of the adult population, because one or the other may be more likely to die young. It's even less the case that all males, or all females, are equally likely to pair up and have offspring of their own.

This disparity is known as reproductive skew, and it varies considerably between species, and sometimes even between populations of the same species. At one extreme, it's essentially zero. This happens if the species is basically monogamous, usually because child rearing is a sufficiently draining exercise that being able to share the duties between two individuals is really helpful. It can also happen for what might be regarded as the exact opposite reason - if the species is highly promiscuous so that the females will mate with absolutely anyone, once again, everyone's chances of reproducing are the same. There's just less of that courtship stuff to worry about, off-set by having a single-parent family once you're done.

The Pig Family: Suids, Suines, and Swine

The pigs occupy an an interesting position in the mammalian family tree. The pig family, or Suidae, belongs to the order Artiodactyla, consisting of the cloven-footed mammals and a few of their closest relatives. (I will, at this point, note that I'm going to be using "artiodactyl" in the traditional, non-molecular sense, in this post. Paraphyly be damned, at least for today.)

This is unsurprising, given that pigs do, indeed, have cloven hooves. However, there are other features that almost all artiodactyls have in common, most significantly, that they are purely herbivorous animals with multi-chambered stomachs that they use to "chew the cud". Pigs, however, do not, and while they may not be the only non-ruminating artiodactyls, they are by far the most species-rich group to fit this description.

Traditionally, this was thought to be because they are more "primitive", having evolved before their relatives got round to developing more complex digestive systems. In a more modern way of looking at things, we'd instead note that, compared with other artiodactyls, pigs are omnivorous; they haven't developed more efficient ways of digesting tough plant matter because they don't need to. That they've survived as well as they have, evolving over many millions of years without ever being wiped out, shows that this has been a pretty successful tactic for them.

Miocene (Pt 5): Hyenas in the Treetops

The first hyenas somewhat resembled this African civet

When we think of prehistoric carnivorous mammals, the first image that probably pops to most people's minds is that of sabretooth cats. It will therefore be no surprise that, were we to visit Middle Miocene Europe, one of the most widespread carnivores that we would find would be a moderately-sized cat-like animal with enlarged, serrated canine teeth in its upper jaw. What might be a little more surprising is that it wouldn't actually be a sabretooth cat.

The animal was called Prosansanosmilus, and it is known to have lived at least across what is now western Europe, from Spain to Germany. It, or its immediate ancestor, had probably first evolved in northern Africa, and arrived in Europe not long after that continent had collided with its northern neighbour - one of many animals to cross over as part of the so-called "Proboscidean Event". In life, it would surely have looked much like a cat, albeit with shorter legs and flatter paws less suited to pouncing and other rapid movement. But, in fact, it was not a cat, but a member of a family that, like the bear-dogs, no longer exists; that of the barbourofelids, or "false sabretooths".

The Strong, Silent Type?

Compared with many other kinds of animal, mammals can often have complex social lives. While many kinds of mammal live in packs or herds, with sophisticated dominance hierarchies and the like, the most complex of all mammal societies (at least as defined by we humans) belong to species belonging to one of just three mammalian orders. It's likely no coincidence that these also happen to be the three orders with the proportionately largest brains.

Perhaps the most obvious of these are the primates, the group that includes our own species. Many species of monkey have flexible social structures where members join and leave groups, adjusting their social positions accordingly, and relying on sophisticated interactions with one another to keep everything functioning. However, the social lives of cetaceans (whales, dolphins, and porpoises) can be equally complex, with, for example, multi-level associations between different pods. The third group to exhibit this sort of behaviour are the elephants.

Making Hay on a Mountaintop

As I write this, the weather across much of the US is not great. According to Google, it is, right now, -12°C (10°F) in Washington, DC, and that's ignoring the effects of wind chill. And it's a nippy 16°C (61°F) in Arizona... okay, so perhaps that latter one isn't the best example. But the point is, this is harsh, and, if it isn't fun for humans, then it isn't for wild animals, either.

Indeed, winter in general is a tough time for animals living in temperate climes, as much due to the lack of food resources as to the need to shelter from the cold. There are a number of different strategies they use to mitigate this time of enforced starvation. Some animals, of course, simply brave the conditions, using thick winter coats, and perhaps some means of digging out food from beneath a blanket of snow. But others take more active steps, and there are basically three ways of doing this. One is to hibernate, so that you don't need much in the way of food until the spring. A second is to simply move elsewhere, either migrating to warmer climes or, if you live on a mountain, just heading downhill a bit.

A third approach is to collect food in the autumn and then store it somewhere through the winter, so that you have ready access to it. This, naturally, poses a number of problems. You have to remember where you put the food, hope that somebody else isn't going to find and eat it, and ensure that it doesn't spoil. Even so, a number of smaller mammals do exactly this, and it's clearly something that works for them.