The Genomics of Yellow Bats

In terms of species, bats are the second-largest order of mammals, after the rodents. New species are identified all the time, due in part to the relative difficulty of closely examining night-flying mammals, many of which sleep in hard-to-access caves. The current total stands at over a thousand, representing over 20% of all known mammal species. 

Within this huge group, there is, perhaps, rather more diversity than many people realise. While bats have probably not received the same level of attention as some other mammal groups, scientists have nonetheless long attempted to disentangle the relationships between all these subgroups. (Also, when I say they have received less attention, there's a mammal-centric bias here; it's probably still a lot better than, say lizards, let alone millipedes or the like). 

A Brief History of Zokors

The rodents are the largest group of mammals, in terms of number of species, and they are divided into several families. Some of these are familiar, such as the mice, voles, squirrels, and gophers, but others are much less so, at least to the majority of people in the West. This includes, for example, the zokors.

There are a couple of reasons why zokors are not as well-known as some other rodent groups. For one thing, they only live in northeast Asia, an area that it's fair to say doesn't receive much attention in the Western world. For another, even if you did live there, you wouldn't see them very often, because they are burrowing animals that don't like coming to the surface if they can help it. Rather like moles, you might see the mounds of earth they leave, but not often the animal itself.

Climate, Cloud Forests, and Cotton Rats

The Cricetidae is the single largest family of mammals in terms of the number of species, at least according to the current count from the American Society of Mammalogists. While the name translates as "hamster family", the great majority of species are not themselves hamsters. In fact, there are five subfamilies of cricetid: the hamsters, the voles, and no fewer than three with members that basically look like mice or rats... even though the true mice and rats belong to the second-largest family, the Muridae.

The largest of these subfamilies is the Sigmodontinae, consisting of mouse and rat-like animals primarily native to South America, although one species lives as far north as Virginia, and several others reach Arizona and New Mexico. The group is named for the S-shaped pattern on the molar teeth and was originally coined as the genus name for the cotton rats in 1825.

American Moles in a Spanish Crater

Eastern mole

Moles are unusual animals. Most species are highly adapted for digging, spending almost all their lives underground, making them vulnerable to predators when they have to venture onto the surface. One might think, therefore, that they would not have dispersed widely across the globe and that it should be easy to trace their evolutionary history.

However, this is not the case. For one thing, moles are found across the Northern Hemisphere, in Europe, Asia, and North America. A million years is, after all, a very long time and moles have been around far longer than that - including some times when the Bering Straits were dry land. 

Oligocene (Pt 13): The First Porcupines

Prosotherium

The dawn of the Oligocene is marked, in part, by the formation of a deep water channel between South America and Antarctica. To what extent there had been a true land bridge between the two continents in the preceding epoch is debatable, but the separation was certainly more complete than it had been previously, beginning a long period of isolation that allowed unique animals to evolve and flourish. Furthermore, most of the large mammal groups we are familiar with today originated on the northern continents, so much of the fauna of South America was already strange to modern eyes.

 

Much of it, but not all. The exact date of the oldest rodent fossil from South America has been disputed, but recent analysis suggests that it may have lived shortly after the beginning of the Oligocene. How it reached the continent is also unclear. Logically, it must have made a long sea journey, presumably clinging to some storm-tossed piece of debris, either from North America or Africa (the Atlantic being narrower then than it is now). The latter seems the more likely, since South American rodents are more closely related to the African sort than to their equivalent northern counterparts.

Unravelling the History of Seals

Allodesmus, a desmatophocid

Trying to determine the largest patterns in evolution can be a daunting task. Here, we often want to look at large numbers of species, comparing the living ones and filling in the gaps with fossils that are often incomplete, ambiguous, or that simply haven't been discovered yet. As a result, there are several big transitions in mammalian evolutionary history that we'd like to get a better look at. Bats are a significant case in point; their small fragile skeletons don't preserve well if we want to see more than teeth, and how they developed their forelimbs into wings remains obscure.

With some groups, however, we do have sufficient fossil evidence that we can look at a whole group of animals and get some idea, not just of how it originated, or where it fits in the larger mammalian family tree, but what ups and downs it has faced over the course of its existence. This can tell us what alterations in climate or geography drove changes within the group and how and when particularly evolutionary innovations developed.

Squirrels, Advance!

The rapid growth of human population over the last century or so has led to a decline in many species. As I talked about last month, however, some animals can live alongside us even in urban environments, and there are many more than can tolerate us in rural - yet not truly wild - habitats, such as cropland or pasture. Any species that can do this clearly has an advantage, in many cases being able to move into new parts of the world previously inhabited by some similar, but less human-tolerant species. Thus, we can see some native species replaced by foreign invaders, as has happened, for example, with mink in continental Europe and jackrabbits in the American southwest.

In Britain, the most familiar example of this is probably the replacement of our native red squirrels (Sciurus vulgaris) by invasive eastern grey squirrels (Sciurus carolinensis). Red squirrels were once common across the British Isles, but have now vanished from most of England and Wales, surviving in the far north of England and a few pockets elsewhere, but otherwise replaced by the greys. In large part this is due to the greys carrying a virus to which they are immune but the reds are not, but simple competition is another factor.

Flight of the Fossil Pelicans

Dalmatian pelican

Pelicans are distinctive birds with long necks, short legs, and a remarkably long beak the bottom half of which is attached to a large extensible pouch for holding captured fish. They are also large, with even the smallest species having a 180 cm (6 foot) wingspan and the largest being half that again. They are, of course, water birds, with many living along coasts or in brackish waters, but others found in lakes and rivers far inland.

They are also not mammals, which is a timely reminder that, yes, this is the post that will be live on 1st April, when I switch things about for one post a year.

Rise of the One-Toed Horses

The horse family contains, depending on your definition, just seven or eight living species of wild animal. If you count them separately, you can add the two domesticated species to those (that is, the horse and the donkey) but that's it. Moreover, all of these species are so closely related to one another that they can interbreed, albeit usually to produce sterile offspring, and so are traditionally placed into a single genus: Equus.

The genus is noted for its members having just one toe on each foot. The story of how this happened, and the number of toes became reduced, is one of the most frequently repeated in mammalian evolution, although the detail may be more complex than is sometimes presented. The story of how the genus evolved since that point, however, is much less so.

The Rarity of Gophers

What exactly does it mean to say that a species is "rare"? The general idea, of course, is that it must have a lower total population than some species that is "common", and we can certainly argue over where to draw the line between the two. But, even then, rarity can manifest in different ways and that may have an effect on our perception of it.

Take the tiger for example. Today, this is undeniably a rare animal, and it's internationally listed as an endangered species. But go back two hundred years, and tigers were found across southern Asia from the easternmost parts of Turkey to the Russian Far East. They stretched from the deserts of Central Asia to the jungles of Java. But even then, if you'd gone to any of these places, the chances of actually meeting a tiger weren't all that high. Tigers are big predators, and they need a wide area to find enough food to eat. So they may have had a high total population (certainly compared with today) but they weren't exactly abundant in any given locality. Does that count as being "rare"?

Pennsylvania Elk with a Wyoming Accent

We're familiar enough with the idea that humans in different parts of the world speak with different accents and vocabulary, even if they are otherwise speaking the same language. ("Faucet, railroad, trashcan, truck, don't say 'sidewalk' or you suck.") This is true of all languages that are spread over a sufficiently large geographic area; for instance, European and Brazilian Portuguese are at least as different as UK and US English. Even within a single national dialect, we can often distinguish local accents and some differences in spoken grammar and terminology - few native English speakers could confuse a blue-collar Texan with a New Yorker.

Since animals don't have language in the human sense, we might not expect the same thing to be true of them. Animals have distinct vocal repertoires, but these are largely instinctive, and a cat goes 'miaow' regardless of where it lives. (Well, arguably it goes 'meow' if it's American and 'nyan' if it's Japanese, but you get the point). It's perhaps not surprising that there is variation between individual songbirds of the same species, or among cetaceans, given the complexity of their calls, but we might not think of it among terrestrial mammals.

Oligocene (Pt 2): Europe's Big Break

Eomys

The dawn of the Oligocene is marked by a sudden cooling of the Earth's climate, of which the most obvious consequence was the creation of the Antarctic ice sheets. These locked up so much water that sea levels dropped worldwide, reshaping coastlines. Nowhere were the consequences of this more apparent than Europe, despite its great distance from Antarctica.

Prior to the Oligocene, it would have been possible for a hypothetical traveller to sail from what is now the eastern Mediterranean, through the Paratethys Sea (now the Black and Caspian Seas) due north and into the Arctic Ocean. The body of water that made this possible, the Turgai Strait, was already becoming shallower and narrower as the Oligocene approached, and the sudden dip in sea level finished it off altogether, closing off the sea route that had once run along the eastern flank of the Ural Mountains. 

When White-footed Mice Invaded Michigan

When I'm describing a particular species of mammal on this blog, one of the first things I usually mention is where in the world it lives wild. Clearly, there are differences in the fauna of different continents or specific islands. Cougars, black bears, pronghorn antelope, and coyotes are all common enough in the US, but don't live in Europe. We have Eurasian and Iberian lynx, but not bobcats and Canada lynx. There are bison in Europe, but they're a different species than the American sort, and we only have wild raccoons because some were deliberately released in Germany in 1934. 

Clearly, the existence of the Atlantic Ocean is not to be sniffed at. However, this applies on a smaller scale, too, where some physical barrier that's some way short of an ocean, but is still significant, prevents an animal from advancing further across its home continent than it might like. 

And then there's the fact that animals have particular requirements as to the climate and vegetation of their native areas - even if the vegetation is only affecting the prey animals that they themselves need to feed on. The difference between this and the physical geography of rivers, mountains, and so on, is that it's changing over a much faster timescale, especially in recent decades. Animals may be forced to move to new areas, which can be a problem if the physical geography prevents them from doing so and can be a problem for other reasons even if it doesn't.

The Last Pangolin in Europe

Ground pangolin

Pangolins are undoubtedly odd creatures. Most obviously, there's the fact that they are covered with an armoured sheet of keratinous scales, making them look somewhat like an animated pine cone. No other mammal has this feature or anything much like it. But, even ignoring this, they are still unusual, with their narrow diets, conical snouts, digging claws, and long, broad tails. 

The animals that they most resemble are probably anteaters, especially the smaller species. At one time, they were even classified together with the anteaters, but there are some significant skeletal differences, especially in the structure of the backbone that indicate they are clearly distinct. Furthermore, anteaters originated in South America, while pangolins are known only from Africa and Asia, so it's long been recognised that the resemblances are actually due to parallel evolution, with the animals having a similar diet.

Out of the Amazon: A History of the Opossums

Tate's woolly mouse-opossum,
a marmosin species

When most people think of marsupials, it's likely that Australia is the first place to spring to mind; the land of kangaroos, koalas, and wombats among many others. In fact, even the "Australian" marsupials aren't restricted to that country, since they are also found further north, notably in New Guinea - which, for example, has its own species of wallabies. But, more significantly, marsupials are also found outside of Australasia, in the Americas.

The best known of these American marsupials is surely the Virginia opossum (Didelphis virginiana). This lives across most of the US outside of the western mountains and interior deserts, and is also found just across the border in parts of southern Canada, through the whole of Mexico, and well into Central America. It's the only species of opossum found north of Mexico, but it's very far from being the only species of opossum anywhere.

Last Gasp of the Australian Seals

Today, true seals only live much further south

In common English parlance, the word "seal" refers to a range of animals that, scientifically speaking, constitute two different, but related, mammal families. (A third related family, which today includes only the walrus, is distinctive enough that most people probably don't think of them as "seals" in the regular sense). I've previously written a post that goes into detail about what the difference between these two families is, but the technical names are phocids (for "true" or "earless" seals) and otariids (for the sea lions and fur seals, both of which have visible ears).

For simplicity, I'm going to refer to these two groups as "true seals" and "sea lions" in this post, although you should be aware that the so-called fur seals fall into the latter group. We've long known that "fur seals" aren't really a specific type of animal, but are at least two different kinds of sea lion that coincidentally look a little different from their relatives.

The Case of the Missing Sengi

The rediscovery of a species of mammal thought "lost" for almost 50 years was a significant enough story this week to appear (briefly) on the front page of the BBC News website. I'm not sure how much further I can add to the BBC story in terms of detail, but perhaps I can put it into context, as well as providing it for those who may not have seen the original. So here goes.

To start with, what exactly is a sengi?

Sengis used to be (and often still are) called "elephant shrews". The term is falling out of favour because they aren't literally shrews, in the sense of belonging to the actual shrew family, although, as descriptive terms go, it's not a bad one. Since the late '90s most scientists, when they aren't using the more technical term "macroscelidean", instead use the Swahili name for the animal, which is also the one I'll stick with.

Miocene (Pt 19): When Rhinos and Giraffes Went South

Prolibytherium

At the dawn of the Miocene, 23 million years ago, Africa was a very different place than it is today. This was as much due to simple geography as anything else. For one thing, the Sahara Desert didn't exist yet - even the most extreme estimates suggest that it didn't begin to appear until the Late Miocene, and it may well have not have formed until at least the Pliocene around 4-5 million years ago. Before this time, much of the continent was probably covered in warm, damp, forests interspersed with patches of more open woodland and scrub.

More significantly, perhaps, Africa was still an island continent, separated from Eurasia by a body of water called the Tethys Seaway. It had been like this, isolated from the rest of the world, for millions of years, during which time it had developed its own unique animal life, quite different from that elsewhere. At the time, the same was true of South America (and it still is for Australia), but that continent retained its unusual animals for much longer, not contacting the north until as recently as 2.5 million years ago, shortly before the first of the Ice Ages. When that did eventually happen, it led to the Great American Interchange, which set the scene for much of the American fauna we see today.

The Many Kinds of Extinct Marsupial

Simosthenurus, a short-faced kangaroo

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

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

Small British Mammals: Rats!

Brown rat

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

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