Prehistoric Mammal Discoveries 2021

Lesmesodon, a weasel-sized hyenadont.
A new species from Early Eocene France was
 described this year

And so another year approaches its conclusion and the pandemic seemingly isn't done with us yet. I had to self-isolate after a positive test myself for a couple of weeks (no symptoms, though) but if there's one thing that doesn't interrupt, it's blogging, so everything went smoothly here. But now it's time for what's becoming a traditional look at the paleontological discoveries of the past year that didn't get covered here but are worthy of at least a brief mention.

Large Herbivores

When we think of vertebrate fossils, the first thing that pops to mind is almost certainly going to be a skeleton of some kind, or perhaps just part of one. But there are also such things as ichnofossils - fossilised remains of how an animal affected its environment that no longer include any physical part of the animal itself. Perhaps the most obvious of these are fossil trackways - footprints of long-gone animals preserved in mud or other soft material that has since turned to stone. A study published this year examined the tracks left by two species of fossil horse. One of them, a one-toed close relative of the living species inhabiting southern Canada during the Ice Ages, turned out to have been galloping at around 34 kph (21 mph), which is quite fast for its small size (perhaps it was running from something). More significantly, however, the three-toed Miocene horse Scaphohippus was using a relatively unusual gait called the "rack" typically only seen in specialised domestic breeds today. 

Miocene (Pt 30): Horned Armadillos and Marsupial Dogs

Borhyaena

At the dawn of the Miocene, South America had been an island continent for many millions of years, allowing many strange forms of mammal to evolve that were not found elsewhere. Few of these survived the creation of the Central American land bridge, allowing more familiar creatures from the north to replace them. Some of those that did, such as the ground sloths, failed to make it through the Ice Ages, but there are exceptions still around today - descendants of ancient and peculiar animals that first originated in South America.

Among these are the armadillos, a group that was already well-established by the Early Miocene and with many living species, including one that has successfully colonised parts of North America. Miocene armadillos were perhaps more varied than those alive today, largely due to the existence of the glyptodonts. 

Mouse Lemurs in the Mangroves

Well over 6,000 species of mammal have currently been described, many of which have only been confirmed as distinct species in the last few decades. There is undeniably a trend in the 21st century towards "splitting" of species along comparatively fine dividing lines, but it's also the case that this has been supported by advances in genetics and the like that have made it easier to tell when two groups of animals really are different, and not interbreeding.

But the corollary to this is that many of these species look extremely similar. It's often the case that, once a new species has been described on the basis of genetics, we can point to physical differences between it and whichever species we split it off from. But these are necessarily minor differences, perhaps previously thought sufficient to justify a designation as a subspecies, but more likely not noticed at all. Given the physical similarities, we'd expect that their diet, behaviour, and so on would also be similar - they are, after all, very close relatives.

All the World's Deer: A History of the Deer Family

Megaloceros

Over the past year, I have described no less than 53 living species of deer, seven of which are currently considered endangered and one of which, bar a few park escapes, exists only in captivity. And that's excluding Schomburgk's deer which. as I noted, probably went extinct in 1938, and certainly didn't last long beyond that if it didn't. It's the only known species of deer to have gone extinct for centuries, although it might not be the last to do so. But there are, unsurprisingly, given their large size and distinctive features, a great number of extinct fossil species of deer that we know about.

Further along in this blog I have posted a summary of the family tree of the living species of deer. This is derived from molecular and genetic studies, but it turns out to map reasonably well to what we would have guessed purely from looking at the animals and their skeletons, which is good news if we want to try and place fossil deer into it. The first thing that's apparent from the tree is that, as predicted back in the 19th century, there is a deep split within it, representing the two subfamilies: the cervines (at the top in the diagram) and the capreolines.

Brains of the Monster-Teeth

Dissopsalis, another member 
of the "monster-tooth" family

Among the distinguishing features of mammals, as compared with other vertebrates are the larger relative size and greater structural complexity of the brain. It's worth pointing out at the outset that many birds are as capable as mammals of complex behaviour despite not possessing the brain structures we'd otherwise associate with such things so that we can't solely use brain anatomy as a proxy for things like 'intelligence'. But, if we're looking only at mammals, brain anatomy can tell us quite a bit and it's probably fair to say that it does distinguish us from, say, reptiles.

Arctic Sonar Beams

Dolphins and porpoises are well-known for using biosonar to navigate their way around and detect the fish on which they feed. There are a large number of different dolphin species, with well over 30 in the Oceanic dolphin family alone, which includes not only the regular-sized species but also much larger "dolphins" such as the killer whale. Given this physical variety, and the variation in habitats between the different species, it's unsurprising that there are also many variations in the exact details of the sounds they emit and how they use them.

Much of this variation seems to date from the Middle to Late Miocene when both dolphins and porpoises underwent a rapid increase in the number of known species. This may be related to the loss of the connection between the Mediterranean and the Indian Ocean, creating a change in the worldwide circulation of water and corresponding changes in the habitats available to these animals, allowing them to exploit new opportunities.

All the World's Deer: The Largest Deer and Other Oddities

Moose

It will probably come as no surprise that the largest species of deer alive today is the moose (Alces alces), confusingly known as the "elk" in some parts of Europe. The latter is, of course, the original English name for the animal, and remains, more or less, the name for it in languages such as German and Swedish today. The word "moose" comes from one or more of the Algonquian languages and entered English no later than the 17th century, although why Europeans chose to rename the animal they already knew about rather than come up with a new name for the novel American beast that looked like a red deer is unclear.

At any rate, moose are undeniably large, considerably larger than the American elk. They typically stand around 200 cm (6' 6") at the shoulder, with females not much shorter than males. The males are, however, significantly bulkier and more muscular, with a full-grown bull typically weighing between 300 and 600 kg (660 to 1300 lbs) and females around 25% less. The occasional exceptional individual can, of course, be much larger than this but, even ignoring those, that's pretty big for a deer.

Flesh-eating Bats

Greater noctule bat

(Well, it is Halloween...)

At least in the parts of the world with a temperate climate, the great majority of bat species are insectivorous. Of course, there are a number of vegetarian bats, especially in the tropics, including the large fruit bats of the Old World as well as smaller, often fig-eating, species in the Americas. But insect-eating does seem the default, even though there is general agreement these days that bats are more closely related to the larger carnivores and to the hoofed mammals than they are to the other small insectivores, such as shrews and hedgehogs.

From an ecological, trophic web, perspective, insectivores are a type of carnivore - after all, they eat other animals, even if they're small ones. But, when talking about mammals (and similarly sized vertebrates) most researchers tend to draw a distinction between those that hunt invertebrate prey and those that eat comparatively large vertebrates. So there's a distinction between leopards and killer whales on the one hand, and shrews and anteaters on the other.

Miocene (Pt 29): Fake Elephants and Otter-Shaped Herbivores

Nesodon

At the dawn of the Miocene, South America was home to no fewer than three orders of moderate to large hoofed herbivore, compared with the two it has today (one containing the deer and llamas, the other including the tapirs). There is, of course, a degree of arbitrariness in what gets designated an 'order' as opposed to some other ranking. But nonetheless, these animals were distinctive, related to the two orders of ungulate we have today, but different from both of them. 

Two of these South American groups would outlast the Miocene, only dying out relatively recently. These were the litopterns and the notoungulates, both of which bore most of their weight on the third toe of each foot, and which may, indeed, be related to the group containing the tapirs, horses, and rhinos, which does the same today.

All the World's Deer: Small Deer of South America

Grey brocket

Deer first entered South America when that continent first connected with its northern counterpart a little over two million years ago. Finding nothing similar already there, they rapidly diversified into several distinct species, taking advantage of a wide range of different habitats. Many of the resulting species were medium to large animals, resembling their northern relatives, such as white-tailed and mule deer. But others instead took on a role closer to the muntjacs of eastern Asia. 

How many species of these small South American deer are truly distinct is a question that is not fully settled yet. In common with the scientific fashions of the time, a great many species were named in the 19th century, only to be merged in the 20th and then split apart again in the 21st (not always along the same lines, of course). As a result, many of the species we recognise today weren't considered such until recently and have not been individually studied to any great extent beyond demonstrating that they exist. On the other hand, the reason that we confused them for so long - and still aren't entirely sure how many they are - is that they are all quite similar. This is especially true of the various kinds of brocket, all of which are currently placed in the genus Mazama.

Baby's First Dive

Perhaps the most distinctive feature of mammals is that they provide their young with milk. This allows the young mammal to continue growing after it has been born, but before it is ready to fend for itself. The downside, of course, is that it leaves the infant entirely reliant on its mother for survival, something that we don't see, for example, in most reptile species. 

At some point, however, the infant has to survive on its own. Before it can truly leave home it needs to be able to find its own food, so there's going to be a period between it feeding entirely on milk and it becoming fully independent during which it's learning the necessary techniques of foraging or hunting. We see something similar in birds; while they obviously don't produce mammalian milk, young birds do necessarily rely on their parents for food until, as a minimum, they get the hang of flying. (It seems plausible that the same was true of pterosaurs, although there is evidence that at least some species learned to fly very quickly and that the period of dependence was correspondingly short).

While the reliance on suckling means that all mammals do this to some extent, the closest obvious analogy to birds would be bats - and, indeed, it does take them time to learn how to fly. But another group of mammals that has to learn how to do something nearly as dramatic before becoming self-sufficient are the pinnipeds (seals and their relatives).

Why Polar Bears Still Make Dens

Hibernation is something that's generally associated with smaller animals, such as bats and rodents. It's likely to be a particularly useful trait for them, since they otherwise need to eat regularly to survive and this would be difficult in winter. Bears are a clear exception to this, snoozing away the winter despite being particularly large animals, and it seems that hibernation has been a key feature of their evolution for some time, distinguishing them from other carnivorans, such as wolves, that live in similar climes.

One of the first things we have to point out in this respect is that it isn't universally agreed by scientists that bears do, in fact, hibernate. This is obviously a debate about terminology, rather than the bear's actual behaviour, and it hinges on whether a bear's body temperature drops enough while it's denning for the activity to be truly considered as "hibernation". It seems fair to say that the usual tendency these days is to consider that what they're doing is close enough to count, but not everyone agrees. For today's purposes, however, I'm going to use what some might argue is a layman's understanding, rather than a strict biological term.

All the World's Deer: Muntjacs

Red muntjac

For many people, the word 'deer' likely conjures up a medium to large animal with large branching antlers in the males. This fits the description of not only red deer and fallow deer in Europe and white-tailed deer in America, but also many species less familiar to those of us in the West, such as barasingha, sambar, and huemul. But there are a number of animals much smaller than these that are nonetheless indisputably deer. The smallest species of deer in Europe is the roe deer, but even smaller species live further east, most of which are collectively described as muntjacs or "barking deer".

Muntjacs were first scientifically described in 1780, from a specimen collected in Java. Muntjacs, of course, live much further afield than this, and, over the years, some of those living elsewhere were split off and given their own species names. As per the standard rules, the one that's found on Java kept the original scientific name, modified only when muntjacs as a whole were given their own genus in 1810. We now call this the red muntjac (Muntiacus muntjak) and it remains one of the best-known species, not least because it's the most widespread.

Before the Monkeys: Primates in North America

Anaptomorphus,
an omomyid from Wyoming

The primates are one of the larger groups of mammals, with literally hundreds of living species known. Naturally, there is a great deal of diversity across the primates but, at the highest level, we can divide them into two main suborders. These used to be referred to as the "lower" and "higher" primates, but that's misleading because the so-called lower primates have been evolving for just as long as the higher ones. It isn't as if they gave up one day and stopped evolving towards some ultimate goal of becoming human. 

So, instead, when we aren't using the technical terms strepsirrhine and haplorrhine, today we tend to call them "wet-nosed" and "dry-nosed" primates, based on whether their nose is moist like that of a dog or not. When most people think of primates, however, it's likely the haplorrhine, or "dry-nosed" primates that they think of first, since this is the group that includes all the monkeys and apes - as opposed to lemurs and the like.

Hanging Out in the Heliconias

Bats are usually sociable animals. Since large caves are relatively rare, when bats find one, literally millions of individuals can pack themselves into a single one, often comprising several different species. But the shortage of suitably large roosts means that many cave-dwelling bats will roost elsewhere including, in human-dominated landscapes, inside attics or other manmade spaces. Furthermore, of course, many bats don't live in caves at all, spending the day roosting in trees or other suitable sources of shelter.

One might think that these tree-dwelling bats would be less sociable than those forced to cram themselves into caves. But, while it's true that they certainly don't tend to form colonies numbering in the millions, this doesn't mean that they live on their own. In some species, the males do in fact do this, following a pattern that's often seen in other social mammals, while the females gather together in maternity roots or breeding colonies. But very few bat species are entirely solitary, with both sexes living alone and, when bats do gather together, the exact structure of their social groups varies considerably between species.

All the World's Deer: Roe Deer and Reindeer

Roe deer

Of the three species of deer native to Britain, the one that's most often overlooked is probably the roe deer (Capreolus capreolus). In fact, it's a common and widespread animal, being found in every major country in Europe except for Ireland, Iceland, and Malta. It's absent from the other Mediterranean islands, too, and doesn't stray far into Russia, but it is found in northern Turkey, and both the Caucasus and Kurdistan regions further east. 

One of the reasons that roe deer aren't so easily brought to mind as fallow or red deer is probably just that they're so much smaller. In fact, they are smaller than any species of deer native to the US or Canada, and by some margin. A fully grown roe deer buck stands no more than 85 cm (2' 9") high at the shoulder, and most are smaller, as of course, are does. They weigh around 25 kg (55 lbs), and have a graceful and slender body compared with most other small deer. The hind legs are slightly longer than the front ones, a feature that's thought to help them creep through dense undergrowth.

Miocene (Pt 28): Miniature Super-horses and the Dawn of the Guinea Pigs

Thoatherium

For most of the Age of Mammals, South America was an island continent, separated from its northern counterpart by a wide sea. Even at the dawn of the Miocene, 23 million years ago, this isolation had already lasted for a long time, and the seas to the north were already a formidable barrier, with just a few islands where Central America is now. In some respects, the variation in climate across the continent was less extreme, especially because the Andes were not so high as they are today and so cast less of a rain shadow. Even so, there was enough variety that many different kinds of animals lived across its great area.

Indeed, the long separation of the continent from the rest of the world meant that it had had plenty of time to develop its own native animals. Whereas, in most of the rest of the world, animals of broad types we would still recognise were already around (early cats, deer, elephants, and so on), most of the larger animals of Early Miocene South America would have been much harder to place, since most of their descendants died out long before the Ice Ages, let alone the present. 

Life Lessons from Monogamous Mice

As a general rule, male mammals don't have much to do with raising their young. In many cases, that's because the species in question prefers the solitary life, and the two sexes only meet up to mate before parting ways again. In more social species, males and females may still live in different herds for most of the year, often because they have different feeding requirements and want to avoid competition. Even where are there mixed-sex groups, the males often spend more of their time fighting off rivals than they do actually looking after the young they sire - although, in this instance, they may be helping indirectly by protecting the herd from predators or the like.

But there are plenty of exceptions. 

Of Pandas and Bamboo

Today, there are eight living species of bear. Six of these are "ursine bears", members of a subfamily distributed across the northern hemisphere, and including the familiar brown, black, and polar bears, among others. The other two are distinct enough that modern taxonomists place each of them in their own subfamily, representing lineages that diverged from the common ancestor of the ursine bears a long time ago. One of these is the spectacled bear of South America, the last survivor of a group of American "short-faced" bears, some of which were really quite impressive.

The other, of course, is the giant panda (Ailuropoda melanoleuca).

This is a most peculiar bear. So much so, in fact, that for much of the 20th century it was unclear whether it really was a bear at all - a misunderstanding due to its similarity, and presumed close relationship to, the decidedly un-bearlike red panda. However, we now know that the two animals are not particularly close relatives and the resemblances between them are largely due to the fact that they share a similar diet.

Early Ungulates of Southern France

Lophiodon

The majority of hoofed animals living today belong to the artiodactyl order, known as the "even-toed ungulates" or, in plainer English, cloven-footed animals. This order includes such animals as deer, antelope, cattle, and pigs, as well as some of their non-hoofed relatives, such as camels. In comparison, there are relatively few living species of the perissodactyl, or "odd-toed ungulate" order, which today consists only of the horses, rhinos, and tapirs.

Yet, as so often, this group was once more diverse. Not only were there many more kinds of (for example) rhinoceros, but there were entire families of perissodactyl that are no longer with us. It is also an ancient lineage, on a par with other major groups, such as the primates. Molecular studies allow us to make some educated guesses as to when the horse-like and rhino/tapir-like perissodactyls last shared a common ancestor, and this turns out to be around 56 million years ago, at the dawn of the Eocene, not long after the non-avian dinosaurs had gone extinct. While this is just an estimate, it also happens to be not much older than the earliest identifiable fossils of the group, so there's a good chance it's fairly accurate.

All the World's Deer: Deer from the Grasslands, Swamps, and Mountains

Pampas deer

In 1758 Swedish naturalist Carl Linnaeus was able to describe six of the species of deer we know today. Five, of these, perhaps unsurprisingly, were the five species native to Europe. What may be more surprising is that the odd one out isn't the widespread white-tailed deer, or even one of the Asian species, but one from South America. (As an aside, he also identified two species of what he thought were deer living in Africa. One may not even be real, and if it ever was, was probably a misidentified antelope. The other is very definitely real, but is no longer considered to be a 'deer').

That one exception is what we now call the Pampas deer (Ozotoceros bezoarticus). These live, or at least used to, across much of central South America from central Brazil to northern Argentina. Today, they are found primarily in scattered patches of land across the region, although their numbers are just high enough in total to avoid being formally listed as a threatened species (although the same is not true of all the subspecies). The main reason for this is that their preferred habitat, as their common name indicates, is open grassland... and most of that has been converted into farmland, with some estimates suggesting that as little as 1% of the original habitat survives today, as compared with the late 19th century.

A Good Winter's Sleep

Mammals have an advantage over reptiles in that they don't need the weather to be warm in order to stay active. This makes it easier for them to live in parts of the world that have cold winters, but even then, the scarcity of food at such times of the year means that they often need some additional survival strategy. Some, of course, simply migrate somewhere warmer during the winter - which typically means moving downhill from summer grounds on mountainsides, the long-distance migration of birds being less of an option. Others, such as polar bears, are just good at surviving cold weather anyway, and may not need to do anything significantly different in winter.

But, leaving those possibilities aside, three basic options for surviving the winter present themselves. They could do something behavioural, such as storing food during the summer and coming back to their hidden caches later in the year when food is short. Or they could change physically, such as by building up fat over the summer or having an extra-thick winter coat that falls out in the spring. (And these are not, of course, mutually exclusive).

Coming Down the Mountain

One of the features of behaviour that I've mentioned a few times while covering deer species this year is that, typically, the males and females spend much of their lives apart, only meeting up during the rutting season. While, clearly, many group-living mammals don't do this, deer are hardly unique, with many other species (and not just mammalian ones) having a similar lifestyle. Females gather together in herds, or whatever the group name is for the animal in question, where they can gather together to protect and nurture their young. Males of such species often live in bachelor herds, which are typically smaller.

Sometimes this is due to a simple imbalance in numbers. In species where males monopolise multiple females, a typical herd, while predominantly composed of females, will also have a single dominant male, forcing any subordinate males to live elsewhere. But this is not the case in deer, because, while stags do indeed mate with as many does as they can get away with, they don't live with them outside the rut. Nor are they alone, since other herd animals, such as goats and antelope, often do the same.

All the World's Deer: White-tailed and Mule Deer

White-tailed deer

When I started this series on deer species, I asked some non-experts how many different kinds of deer they were aware of, to see which ones were best known. I got roughly (but not entirely) what I expected, with red deer and fallow deer topping the list. But that's a reflection of where I live; I suspect that, had I been asking Americans, few could have failed to mention the white-tailed deer.

The white-tailed deer (Odocoileus virginianus) is the most widespread and common species of deer in the Americas, and well-known to anyone familiar with the American wilds. They live throughout the whole of the contiguous US, except for the arid south-west, across southern Canada and almost the whole of Mexico. They are also found right across Central America, and into Colombia and Venezuela beyond, reaching the Guyanas and far northern Brazil in the east and as far as Peru in the south.

Miocene (Pt 27): Rise of the Apes

Proconsul

From a human perspective, one of the most significant evolutionary developments of the Miocene epoch was the appearance of the first apes. Exactly when the group first arose isn't entirely clear, but it's either very early in the Miocene or very late in the preceding, Oligocene epoch. Part of the reason for the lack of clarity is, as so often, dispute as to where exactly the dividing line is between apes and monkeys when we go this far back in time. But there also seems to be some evidence that the earliest apes evolved in African jungle habitats, which weren't the best for forming fossils.

An example of this early confusion comes from Dendropithecus, from the Early Miocene of Kenya. Comparatively small, at only around 60 cm (2 feet) in length, and with arms that seem to be adapted to swinging from trees, when it was first named as a distinct genus in 1977, it was thought to be an ancestor of modern gibbons. Despite having a somewhat similar lifestyle and diet, this no longer thought to be likely, and one recent analysis places it as belonging to a very early branch in the ape family tree - just early enough that one could legitimately argue as to whether it really counts as an 'ape' or just a very close relative.

How Giant Rhinos Crossed Tibet

It sometimes appears that just about every sort of animal was larger in prehistoric times. That this cannot be a universal rule is shown by the fact that the largest animal ever to have lived is the blue whale, which is still around today (albeit as an endangered species). Still, it is true that many prehistoric animals were larger than those alive today, and dinosaur researchers do seem to be engaged in a constant battle to find the "biggest land animal ever" - although this is likely a reflection of what sort of palaeontology stories get into the regular news media.

The largest land animal ever to have lived was surely a dinosaur, most likely a member of the aptly named titanosaur group. But what about the largest land mammal? It's hard to know for sure, partly because "largest" is a vague term that could be interpreted in different ways - do we mean weight or linear dimensions? But it's also just difficult to know when all you have to go on is the skeleton, and that's probably incomplete. 

Girl Power in the Monkey World

There are many advantages to an animal of living in a group, such as it being easier to watch out for predators or even drive them away. One of the downsides, however, is that you also have to compete with others of your own kind for access to resources. Clearly, constant infighting is not a good thing and would lead to a rapid breakup of the social group in question. One way that this can be reduced is through the practice of social dominance.

The first formal model of this concept in animal behaviour was described by Norwegian zoologist Thorleif Schjelderup-Ebbe in the 1920s. Having grown up on a farm, he had observed the behaviour of chickens, and, in his PhD dissertation in 1921, he described what is popularly known as the "pecking order". What happens is that, rather than fighting constantly, chickens establish a hierarchy where each animal knows where it stands. If two chickens face off against one another, the lower-ranking, or submissive, bird almost always backs down, allowing the higher-ranking, dominant bird to win without a proper fight. 

All the World's Deer: Deer from the Ganges and Beyond

Barasingha

At least before the rise of intensive agriculture, India, with its lush vegetation, was prime habitat for deer. The constraints of geography - the Himalayas to the north and deserts to the west - keep it separate from Europe and central/northern Asia at least, but it's a very large place, able to support a number of local species. When it comes to deer, there are no less than seven species native to the country, although four of those are only found in the north. Across the great bulk of the country, two medium to large species are common: the sambar and the chital. But there used to be three.

That third one was the barasingha (Rucervus duvaucelii). Fortunately, while I say 'used to be', I don't mean that it's extinct, as its closest relative, Schomburgk's deer is. Just that it's no longer common and widespread. It's primarily a grazing species, feeding in long grasslands and on forest edges and there used to be many of these on the Indian subcontinent. As recently as the 19th century, barasingha were found across almost the whole of central and northern India (aside, of course, from the Rajasthan desert) as well as in neighbouring parts of Pakistan, Bangladesh, and Nepal. They were especially common along the great floodplains of the Ganges and Indus Rivers.

Out of Lockdown

Many mammal species are, by nature, solitary, spending most of their adult lives apart from others of their kind except when mating or raising young. But others are inherently social, living in herds, packs, or simply in mated pairs that live together for a long time even when they don't have children. For such animals, being separated from others is an abnormal situation that can be stressful.

One thing we often see when animals that have been forcefully separated are reunited is that they interact even more than usual, rebounding after their isolation. For instance, male rats kept apart from their friends for a week greet one another with increased petting, social grooming, and anus-sniffing, compared with how they behave on normal days. It probably doesn't come as much of a surprise that something similar is known to be true of humans that have experienced temporary social isolation.

A History of the Honey Badger

Traditionally the weasel family was divided into three subfamilies: the otters, the skunks, and everything else. Sometimes the badgers were added as a fourth subfamily, but that was about it. As more modern genetic analysis came along, showing us some of the underlying relationships that weren't apparent from anatomy alone, it became clear that things were a good deal more complicated than that, and we now recognise about eight subfamilies of mustelid. (And that's not counting the skunks, which turned out to belong to a different group).

The badgers, in particular, turned out to be more varied in their origins than we had previously thought. Their superficial similarities were due to them all having evolved to be heavily-built digging animals, rather than because they all shared one single ancestor. In particular, two kinds of badger, the American and honey badgers, are now recognised as representing their own distinct subfamilies, with just one living species each, and diverging from the other "weasels" very early on - probably before the "true" badgers of Eurasia had first appeared.

Out of Your Hole

Many animals dig burrows. They can be used for shelter when sleeping, or as a safe place to raise young and, while they may take more effort to construct than finding a natural rock crevice or hiding beneath a log, it's often worth it. Especially if you happen to live in an environment - open grassy plains, for example, where such alternatives are hard to come by. Although, admittedly, this does tend to apply only if the animal in question is small; not only would it take more effort for a large animal to dig a burrow, there's less that's likely to eat it, and it would be harder to hide the entrance anyway.

But some small mammals go further than merely digging burrows to sleep in. They spend almost their entire lives underground, being able to feed off earthworms, roots, and the like. It's a peculiar environment to live in, entirely lacking in light, and requiring constant work to maintain, as well as often being low in oxygen. But it is undeniably safe, not just from most predators, but also from inclement weather (so long as you're not somewhere that's prone to flooding). 

All the World's Deer: Endangered and Beyond

Eld's deer

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

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

Miocene (Pt 26): Planet of the Monkeys

Victoriapithecus

The primates are one of the major mammalian orders alive today, with a great many species spread across three continents: Africa, Eurasia, and South America. They have an ancient history, and, even by the dawn of the Miocene, were already divided into the two main groups we have today: the prosimians and the anthropoid primates (most of which are monkeys, or 'simians').

It's probably fair to say that most scientific attention has been paid to the latter of those groups, but we do have a number of fossil prosimians from the Miocene. Madagascar, where most prosimian species are found today, was already an island, and had been since the time of the dinosaurs, but there are few known fossils of the relevant age there to tell us much about the early history of lemurs and their kin. Nonetheless, during the Miocene, prosimians were more widely spread than they are today. 

Mammals That Sense Magnetism

Traditionally, there are said to be five senses: vision, hearing, taste, smell, and touch. From a modern scientific viewpoint, however, this is clearly a significant underestimate, since things are rather more complicated than that.

How many senses even a human can be said to have is a matter of definition, although it's generally agreed to be more than five. An extreme way of counting would be to consider every specific type of sensory cell as representing one 'sense'. This, however, results in the conclusion that vision is four separate senses: one for black-and-white (the rod cells) and one each for the primary colours (the cone cells). This, it's probably fair to say, is not something that's widely considered helpful - although it may well be useful to neurobiologists.

If we don't go that far, then, we can still consider vision, hearing, taste, and smell to be singular senses. It is, however, not uncommon to consider the ability to sense temperature as distinct from the ability to sense that you are physically touching something. Pain can also be considered a distinct sense, since you can obviously 'feel' when you have, say, a headache, but it's hard to argue that that should count as 'touch'.

Naked Aggression

Evolutionarily speaking, it is in the interests of animals to have as many offspring as they can, so long as those offspring will themselves reach reproductive age. However the means for a male to do this may be different from those best employed by females. This is especially true in mammals, because the female has to put considerable resource into pregnancy, lactation, and general care of the young until they are old enough to fend for themselves. The male, however, doesn't have to do any of this, and, in many species, his role in matters may be completed as soon as he's finished mating.

This leads to the concept of sexual selection, where the evolutionary demands on the male may be different than those on the female, leading to different behaviours and appearances. There are often said to be two main driving forces behind such sexual selection. The first is the need for males to compete with one another for access to females, resulting in larger, more heavily built males, often with natural weapons of some kind, such as horns or tusks. The second is driven by the females, when they choose a mate based on some particular feature, leading the males to emphasise that feature in response. (This is, perhaps, most obvious in birds).

All the World's Deer: Deer With Spots

Fallow deer

The fawns of most (but not all) deer species are born with spotted coats, which likely help to camouflage them among the dappled light of a forest. In some species, the spots disappear shortly after birth, while others retain them for a while longer. In five species, however, they keep them all the way into adulthood. I've covered two of these species already: the sika deer of Japan and the um... spotted deer of the Philippines. 

To Europeans, however, the best-known is surely the fallow deer (Dama dama). This is Europe's medium-sized deer, and one of the six original species of deer identified as such in the first list of scientific names in 1758. It lives in woodland areas across most of western and central Europe, preferring broadleaf forests but happy enough with conifers or Mediterranean scrubland. They don't like deep snow, and so aren't found in the Alps or all but the most southerly parts of Scandinavia, but otherwise, they seem pretty adaptable and widespread. Yet, despite being such a familiar animal, they're arguably not really native to the continent.

How Walruses Got Their Tusks

Titanotaria, a tuskless walrus

Few people would argue that the walrus (Odobenus rosmarus) is not a distinctive animal. Indeed, it is so distinctive that, despite there being only one living species, that species has been placed in a "family" all of its own since 1880, distinct from both the seals and sea lions. 

There are a number of features of walruses that make it clear, from a modern perspective, that this was the right decision to make. But the most obvious is surely that they have huge tusks. These are in many ways a remarkable feature, and while other animals, such as elephants, also have large tusks, none that's alive today has anything quite like those of the walrus. 

Walruses have a long evolutionary history, having been distinct from their closest living relatives for many millions of years. Nonetheless, those relatives are, as we might expect, the seals and sea lions and it's apparent that they entered the water long before growing the tusks. Which, in turn, means that the first walruses must have been tuskless. So when and how did this change?

Armadillos Looking for Love

We can tell a lot about animals by simply observing where they go. While studies on wild animals can cover a wide range of different topics, many of which require close observation of what the creature is actually doing, many of the most basic simply require us to tag the animal with some sort of transmitter and watching it move remotely.

Of course, while I say 'basic', this isn't necessarily all that simple to do in practice. You need to capture the animals, ensuring that they aren't overly stressed by the experience so that they modify their behaviour after the fact, and then you do need to spend a lot of time collating all the date, likely over the course of several months. Still, we do have many such studies for most well-known mammals. Some groups, however, have been comparatively overlooked.

Before Owls Ate Mice

Palaeoglaux

Most bird species are diurnal. Doubtless, if you're flying about and don't have sonar, as bats do, it helps to be able to see where you're going. Nonetheless, there are many exceptions to this general rule, and none are more obviously so than the owls.

There are well over 200 living species of owl currently recognised, ranging in size from the mighty Eurasian eagle-owl (Bubo bubo) with a wingspan of up to 180 cm (6 feet) down to the tiny elf owl (Micrathene whitneyi) with a wingspan of just 27 cm (10 inches). They are grouped into two closely related families; the great majority of species belong in the Strigidae family, with just 20 assigned to the barn owl family, the Tytonidae. While there are some internal differences between the two, the most visible in the living animal is that barn owls, unlike regular owls, have distinctive heart-shaped faces.

Both families have been around rather longer than most mammal families have, with fossil representatives dating back to at least the Early Oligocene, around 35 million years ago. The two families are, however, rather like pigs and peccaries, each others' closest relatives, together forming the order Strigiformes. Since few people would deny that a barn owl is, in fact, an owl, it's this order that's really the scientific counterpart of our everyday understanding of the word.

All the World's Deer: Sambar and Rusa

Sambar

Deer are predominantly woodland animals, so it's no surprise that the extensive warm forests of Southeast Asia, with their many isolated islands, are home to a number of different species. Some of these are closely related to the red deer that live in cooler environments further north, so much so that some authors have recommended moving them back into the genus Cervus to join the red deer and their immediate kin. 

Nonetheless, they do seem to form a distinct branch on the deer family tree - although how many species might be in that branch, and even which ones they might be, is debated. For much of the 20th century, just two or three species were recognised, but genetic evidence gathered in the 21st century has made it more obvious that some of the island forms have been isolated from their mainland relatives for long enough to become clearly distinct.

Miocene (Pt 25): The Large Clawed Cat-Cat and the First Dog in Africa

Lokotunjailurus

Today, the hyena family consists of just four species. All of them live in Africa and, generally speaking, they look somewhat like dogs. Three out of the four are scavengers, with powerful teeth adapted for cracking open bones to consume as much of a carcass as possible. The largest and fiercest of these is the spotted or "laughing" hyena, which is the one most people think of when the word "hyena" is mentioned, although there is more variety in the group than that. But even so, with just four species, it's not what you'd call a large taxonomic family.

During the Late Miocene, however, things were very different. It's hard to know the exact number of species that existed, even among the fossils we have, since some of the subtler differences may not be apparent from bones alone. But there were certainly plenty of genera, spread widely across Europe, Asia, and Africa. They were also more varied than today, and their success at the time may well have been due to the fact that actual dogs were still restricted to North America at the time, leaving the hyenas without direct competitors.

How Rodents Can See Ultraviolet Light

Primates, including our own species, have unusually good colour vision. This is thought to be due to the need to identify when fruit is ripe and ready to eat. Most other mammals don't see the world in the same way that we do, having colour vision that's at best limited and often, so far as we can tell, absent altogether. 

But at least some animals do have an advantage that we don't: in addition to visual light, they can also see in ultraviolet.

In terms of physics, there's no real difference between visual light and ultraviolet; the latter simply has a higher wavelength. In a sense, as its name suggests, it's just a colour (or range of colours) that are more violet than violet. Our own inability to see it naturally gives us something of a bias here, but, in principle, there's no real reason why an animal shouldn't be able to see UV light if it would be useful to do so.

All the World's Deer: The Red Deer Species Complex

Red deer

When the first list of scientific animal names was drawn up in 1758, all six known species of deer were placed in the genus Cervus - which is, of course, simply the Latin word for "deer". Over the following decades, as taxonomy became more refined, all but one of those species were moved to other genera, and when the deer family, Cervidae, was named in 1810, it had roughly the same meaning that the genus had had so many years before. As its name implies, though, Cervus was selected as the type genus of the family - the one that defines the archetypal group against which all others are compared. Although newly described species had been added since, the one species that was so obviously deer-like it had never been moved anywhere else thus became, in a sense, the defining species of its family.

The Crab-Eating Fox That Wasn't

There are many species of "fox" native to South America. I covered all of these in a series on the dog family a few years ago and I noted at the time that they aren't really foxes in the sense of being related to the likes of red, Arctic, and fennec foxes. Instead, we know from both genetic and anatomical studies that they are more closely related to the group that includes wolves, jackals, and coyotes. 

The dog family has its origins in North America and it seems clear that what happened here is that some wolf-relative that happened to look a bit like a fox headed south at some point, where all of its remaining descendants live today. North and South America joined up relatively recently, geologically speaking, so it's likely that the origins of the South American foxes actually lie in the North, already looking somewhat like their modern form before they made the trip.

The Tyranny of the Bruce Effect

Monogamy is a relatively rare phenomenon among mammal species. It tends to occur where it requires considerable investment to raise children, whether that be in terms of supplying food over a long period, or careful protection from external threats. If you can spread that effort between both parents, the child is more likely to survive and the species to be perpetuated.

That's common in birds, perhaps in part because they have to physically fetch and deliver food rather than producing milk with the calories from their own diet, not to mention the effort of incubating eggs. But, in mammals, while it certainly occurs in some species (as do the other two options) the most common pattern is polygyny. 

The Toxic Life of an Unusual Rodent

As I've often mentioned before, the largest mammal family, by number of species, is the mouse family, or Muridae. Containing around a quarter of all known mammal species, it's vast and, in many cases, the species are so similar to one another physically that they can only be told apart by genetic analysis. A few years ago, I reported on the largest attempt to determine how this great array of species are related to one another. That particular scheme showed three main evolutionary lineages within the family.

By far the largest are the "murine" or "typical" mice which contains... well, almost everything. According to that particular study, they split from the other members of the mouse family about 18 million years ago, during the Early Miocene. Then, about 16 million years ago, as the Middle Miocene dawned, the remainder split into what are now recognised as two distinct subfamilies: the gerbils and the "deomyine" mice. (The latter look almost exactly like the murine sort, and it took this sort of study to prove that they weren't). 

The Deer Family

Doe (a deer, a female deer)

A little over eight years ago (blimey...) I began a series on members of the goat subfamily, and started it off with a discussion of the difference between horns and antlers. In short, horns are permanent structures, comprised of a central bony core surrounded by a sheath of um... horny material. Antlers, on the other hand, are regrown every year, and once they reach full size and shed the velvet on their outer surface, they consist solely of dead bone, with no sheath of any kind. Antlers are also often branched, whereas 'true' horns never are.

Antlers are, of course, the key defining feature of the deer family, the Cervidae. They are found on (almost) every species in the family, although (almost) only on the males. A large stag with branching antlers is instantly identifiable as a deer, but it may be fair to say that some of the species with unbranched antlers do have a certain resemblance to some of the smaller species of antelope.

Miocene (Pt 24): Of True Elephants and Three-toed Horses

Stegotetrabelodon

The first horses entered Africa towards the end of the Middle Miocene, about 10 million years ago. These have commonly been assigned to the same genera, Hipparion and Hippotherium, as were found in Eurasia at the time, although the fine details of the exact relationships are unclear. Although the latter in particular seems to have been reasonably successful on the continent, a more significant immigration from an African perspective took place later on, around 8 million years ago as the drier climate heralded the start of the Late Miocene.

Sperm Whale Bromance

While there are a few exceptions, there is a general rule among mammals that males travel far from home when they approach adulthood, while females tend to stay in their local neighbourhood. The purpose of this separation is to ensure that, once they become sexually active, the females that a male is going to have the opportunity to mate with aren't all his own sisters or close cousins. Many mammals live essentially solitary lives, so this is merely an issue of the male travelling further than the female when he leaves home; other than that, their social lives aren't really all that different.

In social species, however, the end result is that herds (or other groupings) are united primarily by their female relationships. The females in a herd are likely sisters or other close relatives, while the males have travelled from elsewhere and are not only not closely related to the females, but may not even be closely related to each other, either. Often males spend some time living on their own before they find a suitable herd to join (perhaps because the existing dominant male is getting on a bit) with the result that there's a distinct female-bias in membership of the group.