Sunday, 18 December 2016

New Mammal Species 2016

Reticulated giraffes
2016 has, on the whole, been a bit of a rubbish year. Or so the common wisdom has it; one suspects that, for instance, the deaths of some particularly prominent celebrities at the beginning of the year has heightened our perception of those that died later on (relative to any other given year). And it's probably been quite a good year for you if happen to be a Trump supporter, or a fan of Nigel Farage.

But that debate doesn't belong here, instead, as the year draws to a close, it's time to take a survey of the species of mammal that have been newly discovered this year. Or, more accurately, newly named, since what we generally do these days is find some population of a previously known species that turns out not to belong to it, and to be something else instead. There have, as always, been a fair number of them this year, and there's no guarantee that they'll all stand the test of time, and still be considered valid species in, say, 2026.

My survey is, therefore, inevitably biased, with a just a semi-random sample of some of the species announcements I happen to have come across. Most of them are going to be small animals, since they're easier to overlook in the first place, but there are a couple of quite large ones. And, by "large", I don't mean just "wolf-sized", either.

Sunday, 11 December 2016

Bovines: Prehistoric Bison and Buffalo

Steppe bison, from a cave in Altamira, Spain
In the course of this series I have described 22 species of bovine. Whether that number accurately reflects the number of species alive today depends, in part, on what you consider to be a species - not least whether or not long-term domestication is a sufficiently dramatic thing to constitute the creation a new species. But that's the number I came up with, and it's worth noting that no less than seven of these species - almost a third - are currently considered "endangered", and at high risk of extinction. Indeed, the kouprey may well already be extinct, while the species to which domestic cattle belong is extinct in the wild.

(On that last note, incidentally, I received a note after posting on the subject reminding me of the Chillingham Cattle of Northumberland. These are sometimes claimed to be aurochs, or genuinely wild cattle, but this has no foundation, and, while they have been living wild for centuries, they are actually feral animals, likely descended from escaped medieval stock).

At any rate, there have been many other species of bovine that have gone extinct over the millions of years since their first appearance, in most cases for reasons that have nothing to do with humans. So, albeit with a focus on the genuinely cow-like ones, rather than the spiral-horned antelopes and their kin, today I'm going to look at some of them.

Sunday, 4 December 2016

The Alluring Scent of Bat Pee

Southern long-nosed bat
As I've mentioned many times before, scent is an important mode of communication for many mammals. A great many species possess scent glands of some kind or another, often located on the face or in the ano-genital region. In addition to their variable location, these can be of varying levels of size and complexity, arguably reaching heir apogee in the well-developed glands of animals like musk deer or the defensive sprays of skunks and zorillas. Apart from those that spend their entire lives in the water, some sort of scent producing structures seem to be present in just about all kinds of mammal; even humans have modified sweat glands in the armpits and groin that secrete something different from the normal odour-free sweat produced elsewhere on the body.

Having said that, humans can't really be considered to have scent glands in the sense that some other animals do, and our sense of smell is pretty rubbish compared with most non-primate mammals. We do not, as a general rule, communicate by wafting our smelly armpits at one another. But many other mammals do something that isn't quite so far from that, and in a variety of different ways.

Bats are no exception to this general rule. Many bat species have scent glands, often located on the throat or the upper part of the chest, and they can leave scent marks behind to communicate with others of their kind - often signalling something like sexual availability. By no means all bats have fully formed scent glands, but that doesn't mean that the others don't use scent in some way.

Saturday, 26 November 2016

Bovines: Blue Bulls and the Smallest Bovine

Male nilgai
The bovine subfamily can be divided into two main evolutionary branches. One consists of the truly cow-like bovines, including such things as bison, buffalo, and yak, alongside the regular domestic animal. The other are the "spiral horned antelopes", African species that, despite being more closely related to cows than (say) gazelles, nonetheless have a generally antelope-like body form. But there are two living species that fit into neither of these branches. They are relatively closely related to one another, and so form a third, much smaller, evolutionary branch (usually given the taxonomic rank of "tribe"). Although generally considered "antelopes", both species are native to Asia, unlike their spiral-horned kin.

The larger, and likely better-known, of the two is the nilgai (Boselaphus tragocamelus). Standing 120 to 140 cm (4' to 4'7") at the shoulder, although they are considered antelopes, there is a somewhat cow-like appearance to them, albeit with a much narrower head. Indeed, the scientific name reflects their somewhat odd form, since it literally translates as "cow-deer goat-camel" (in fairness, the two halves of the name were coined separately, and not used together for over 60 years afterwards). They are found throughout India, and in some neighbouring regions of Pakistan and Nepal. They have also been introduced into South Africa, Italy, Mexico, and Texas; while the Italian population died out in the 1940s, and the South African ones remain confined to their ranches, some of those in North America managed to escape, and can still be found wild in those areas today.

Sunday, 20 November 2016

Pliocene (Pt 14): Terror of the Marsupial Sabretooths

As I have described in previous posts, during the Pliocene, South America was nearing the end of a long period of isolation, having been separated from the other habitable continents for millions of years. In the very latest part of the Pliocene, it collided with North America, leading to the massive influx of northern animals known as the Great American Interchange. Until that time, many of the native animals were, to modern eyes, rather strange, evolutionary experiments, that, while evidently successful in their own right, could not compete with the invaders from the north, such as deer, llamas, bears, and big cats.

One of the oddities of pre-Interchange South America, though, was the absence of large placental mammalian carnivores. There were, as I have already noted, a few, since the raccoons somehow crossed the seas between the continents well before the rise of Central America. And, towards the end of the Pliocene, a few other animals narrowly beat the Interchange by island-hopping before the land bridge was completed. But, raccoons aside, none of the large mammalian carnivores we would associate with the continent today had yet arrived.

Sunday, 13 November 2016

Whales in Mourning

Dolphins are social animals
Mammals are by no means the only animals to give their young extended parental care, but it is a feature associated with them more than with most other animals (birds being an obvious exception). This is, in part, due to the fact that young mammals require milk to survive, and that the production of milk is one of the key defining features of mammals. The complex social lives of some mammal species, and the long maturation required for the development of features such as high intelligence are also relevant, and it's no surprise that humans have just about the longest period of juvenile development of any animal - and require significant parental care for a large part of that.

Parental care naturally involves things such as suckling the young, protecting them from predators, and so forth, and it can also include helping them to survive injury. Without the advent of first aid, this may often be ineffective, but it has been observed in a number of species. It becomes particularly dramatic - and, from a human perspective, distressing - when it is apparent that the juvenile is already dead. Here, there is no possible benefit to the young, and likely at least some apparent detriment to the mother in wasted effort, if nothing else.

Sunday, 6 November 2016

Bovines: Bushbuck and More

Of all the many kinds of antelope found in Africa, the one that is most widespread is the bushbuck (Tragelaphus scriptus). Bushbuck are essentially found throughout the whole of sub-Saharan Africa outside of the densest parts of the Congo jungles, the Kalahari Desert, and the drier parts of the veldt and the Horn of Africa. That's a huge range; everywhere from Senegal to Angola, and from Djibouti to the Cape.

Bushbuck are the smallest of the African bovines, sufficiently so that any resemblance to cows beyond the basics true of all antelopes (horns, cloven hooves, and so on) is quite absent. Specifically, they stand 60 to 100 cm (2' to 3'3") tall at the shoulder, with the males slightly taller, and much more heavily built, than the females. They do, however, much more closely resemble their larger immediate kin, such as bongos, having a somewhat similar coat colour, and the same twisted horns that make about a single turn along their length. Unlike in bongos, however, the horns are only found in the males - a feature shared with another close relative, the swamp-dwelling sitatunga.

Sunday, 30 October 2016

Out of Tibet - Origins of the First Sheep

The argali is a species of wild sheep still found in Tibet
Sheep, as I have noted before, are members of the goat subfamily within the much larger group of the bovids. They are, in essence, a special kind of goat that has adapted to living in the foothills of higher mountains, rather than on the steeps-sided peaks themselves. The exact number of species of sheep is debatable, but there are at least five wild ones, plus the domestic animal, for a total of six.

When I discussed the evolutionary history of the goat subfamily a few years back, I talked primarily about the goats themselves, and about the muskoxen, and said very little about how the sheep became separated from the goats, and how they evolved since. A new paper, however, goes into much more detail about the origin of sheep and their fossil history. It is, in fairness, based on just one pair of fossilised horns, but, nonetheless, this is as good a starting point as any, and a sound excuse for me to summarise what we do know about sheep evolution.

Sunday, 23 October 2016

Invasion of the Fire Ants

Small, herbivorous mammals have a hard time of it when it comes to being attacked by larger carnivorous ones. Life expectancies are generally short in the wild, counter-balanced by the ability of most animals to breed like... well, rabbits. Many of their behavioural traits are also shaped by the need to avoid being eaten, including, not just general watchfulness, but trying to do things like foraging where (or when) predators are least likely to be a problem.

On the other hand, predators naturally have an interest in getting round this problem, and the result is a never-ending battle between the habits and skills of predators and prey alike. Over the course of thousands of years, this settles into a sort of equilibrium, changing perhaps only as new species evolve and as the geography or climate change on even longer time scales. Unless, of course, we humans get involved.

Humans can mess up the balance of life among wild animals in quite a number of ways, but the one we're concerned with today is that of invasive species. We purposefully carry species from one part of the world to others, especially when it comes to domesticated animals. Pre-Columbian America had no cows, no domestic sheep (although, of course, two native wild species), no pigs, and no horses or cats. There were dogs, but only because humans had brought them across much earlier. The introduction of all of these animals, and the changes in land use required to support them, have had significant effects on the local wildlife in at least some parts of America, and that's before we include animals deliberately introduced for other reasons, such as fur-farming or hunting, never mind those that we didn't introduce purposefully at all, such as rats.

Sunday, 16 October 2016

Whispering Bats on the Hunt for Nectar

Southern long-nosed bats (L. curasoae)
There are likely three things that most of us think of when we think of bats: they fly, they're nocturnal, and they can echolocate using inbuilt sonar. In fact, only the first of these is universally true of bats; there are (and never have been, so far as we can tell) any flightless bats in the way that there are flightless birds. The other two statements, while broadly correct, are not absolutely true of all living bat species.

Indeed, the bats are the second largest order of mammals, in terms of number of species, after the rodents. This, as might be expected, leads to a remarkable variety in their habits and ecology, even if much of it is not immediately obvious to the layman. There are, under the most common present scheme, no less than nineteen different families of bat, and while many other mammal families have names that can easily be rendered in regular English ("cats", "deer", "marmosets", and so on), those of bats are have to rely on more obscure terms ("funnel-eared bats", "sheath-tailed bats", etc.)

Sunday, 9 October 2016

Bovines: Bongos in the Jungle

Broadly speaking, the more cow-like bovine species tend to be found wild in forested habitats, often with quite dense foliage. In contrast, the antelope-like bovines tend to prefer more open wooded country or scrubland. But these are both very crude generalisations. Plains bison and yak, for example, both live in open terrain, and, on the other side of the coin, there are bovine antelopes that prefer forest to savannah.

Among these is the bongo (Tragelaphus eurycerus), which can be found in three, entirely separate, regions of equatorial Africa. The two main populations live along the southern coast of West Africa, from Guinea to Benin, and across the heart of the Congo Basin and surrounding jungles, from Cameroon and Gabon in the west almost to the Ugandan border in the east. The vast majority of bongos live in these two areas, which are nonetheless separated by over 1,000 km (620 miles) of intervening land (much of which is Nigeria). The third population is found only in a couple of tiny mountain refuges in Kenya, where they cling to the forested slopes, migrating up and down them each year as the weather changes.

Saturday, 1 October 2016

Pliocene (Pt 13): The First Carnivorans in South America

For most of the Pliocene, South America was an island continent. Over the millions of years of its isolation, it had evolved some strange forms of mammal unknown elsewhere. Some, such as the anteaters, armadillos, and sloths, survived the continent's eventual collision with its northern counterparts; most did not. A time traveller visiting the continent during this epoch would find much that was vaguely familiar, to be sure - there were monkeys, rodents, and bats, for example - but also much that was not. This is especially true when it comes to the larger animals of the day.

Even today, South America has no antelopes, zebras, or native goats; the role of "large hoofed herbivore" is taken jointly by deer and by llamas and their kin. Both are introductions from the north, arriving only after the rise of the Panamanian Isthmus in the very latest part of the Pliocene. Their appearance did not spell immediate doom for the native hoofed animals, some of which struggled on until the arrival of humans at the end of the last Ice Age, but the end result was the same, and they are all long extinct.

Sunday, 25 September 2016

Flesh-eating Hippos

Hippopotamuses (Hippopotamus amphibius) are amongst the largest of all land-dwelling animals alive today, beaten only by the elephants, and some of the larger species of rhino. They are also distinctive creatures, with their only close relative today being the pygmy hippopotamus, an animal that many people are likely familiar with, if only because they're popular in zoos. While there are, of course, many extinct species, these two are the only living members of the hippo family, the Hippopotamidae.

In the grander scheme of things, hippos belong to the order Artiodactyla, most of the other members of which, such as deer and cattle, are cloven-footed ruminants. Hippos are neither. Like their fellow artiodactyls, the pigs, they are not ruminants, and they have four functional toes. Unlike pigs, however, the toes of hippos are all more or less equal in size and weight-bearing (in pigs, especially warthogs, the two side toes may be used to help steady the animal on slippery or uneven surfaces, but bear little if any of its weight during regular walking).

Sunday, 18 September 2016

Do Gorillas Have Culture?

Animal behaviour is generally instinctual. Their behaviour is, in some way, wired into their genetics, and doesn't vary from one animal to another. Particularly in mammals and birds, individual animals may be shaped by their life experiences, learning new things as they go. But what they can't do, as a rule, is pass that information on to others. Mothers may teach their young how to do certain things, but that teaching process is itself instinctual, so that all animals of a given species learn more or less the same thing as infants.

A large part of the success of our own species is down to our ability to circumvent this, to build on the knowledge of previous generations. This results, among other things, in the development of culture, differences in behaviour based not on the experiences of only one individual, but of their ancestors, in a way that isn't genetic. Britain and Japan are different culturally, not just because of environmental variation (Japan has earthquakes, for example, and has different mineral resources than Britain) but simply because of the vicissitudes of history, the separate evolution of their languages, and so on.

Sunday, 11 September 2016

Bovines: Spiral-Horned Kudu

Greater kudu (male)
Most "bovine antelopes" - those more closely related to cows than, say, sheep - are collectively referred to as "spiral-horned antelopes", because of the shape of their horns. In many species, the horn makes a single 360° turn once it is fully grown, but others have several twists to the spiral. In elands, the twist is tight, marked clearly by a ridge that runs along one edge, but in no species is the spiral perhaps more evident than in the two species of kudu, where the horns are relatively narrow, with a loose, open curve.

The more widespread and common of the two species is the greater kudu (Tragelaphus strepsiceros). These are particularly large antelopes, with the males standing up to 157 cm (5' 2") in height at the shoulder, and weighing up to around 270 kg (600 lbs). Indeed, they are the second tallest species of antelope, after their relatives, the elands. Females are quite a bit smaller, at around two-thirds of the weight, and standing no more than 132 cm (4' 3"). As with most other spiral-horned antelopes, the coat is a brownish colour, with narrow vertical white stripes on the flanks.

The horns, are, however, their most distinctive feature - the second half of their scientific name means "twisted horn". These are typically about 100cm (3' 3") long in fully grown males, and would be even longer were you to measure them along the curve, rather than in a straight line from the base to the tips. Although the occasional horned female has been reported, this seems to be a rare aberration. Even in males, the horns grow slowly enough that it is possible to age younger individuals by how well they've developed; it takes two years to complete the first full turn, and the final adult form, with two to two-and-a-half turns, is reached by around four and a half years.

Sunday, 4 September 2016

Ancient Otters of Idaho

The common river otters of Eurasia and North America are remarkably similar animals. If you placed them side by side you might notice that the Americans ones are (on average) slightly larger, and have a slightly more bland colour to their coat... but, really, it's not easy. I, for one, wouldn't claim to be able to tell which species a particular photograph was of without additional evidence (most obviously, where it was taken).

It was therefore assumed for a long time, not unreasonably, that they had to be very close relatives. As early as 1843, they had been placed in separate genera, as Lutra lutra and Lontra canadensis, respectively. However, it's worth noting that this is 16 years before the publication of On the Origin of Species, so, when he did so, it's isn't obvious that John Edward Gray was necessarily thinking about how "related" they might be. Indeed, for much of the 20th century it was common to ignore Gray and place all of the fairly typical looking clawed otters together into the genus Lutra.

Sunday, 28 August 2016

300th Synapsida

Here, have a marsupial. Or four.
This is, by my count, the 300th post to appear at Synapsida. Which means that, once again, it's time to look back over the last 100 posts to see what has, and has not, been covered, and where I might be going next. Which, considering that I pick the topic for over half my posts on the same day on which I write them, is likely to be a bit vague, but there you go.

The blog has been running for almost six years now, and has settled into a typical audience of between 200-300 hits per day (whatever the heck that means in terms of actual readers). The most frequently used tags over that period have been behaviour and evolution, although this may just reflect how I tag things. Biogeography, for instance, may well have cropped up in all sorts of posts that I didn't specifically note as such.

Looking back over the last 100 posts, carnivorans have probably been the most common animals covered, although there are also plenty of rodents, not to mention cetaceans, bats, primates, and all the rest. As I mentioned last time, my coverage of the main mammal families has been, if not entirely comprehensive, at least pretty broad. Since then, and ignoring posts on fossil beasts, I think I've added four more families to the list of those with a headline mention, all of them either small or obscure (or both): hyenas, degus, cheirogaleid lemurs, and echidnas.

But still no pigs.

Sunday, 21 August 2016

The Sound of Squirrels

It is, of course, well known that bats and cetaceans use ultrasound to help them navigate the world using sonar. However, there is no particular reason why animals should always make sounds that happen to be in the range of human hearing (and, arguably, some good reasons why they might not want to). So, taking the usual definition of ultrasound as anything higher than 20kHz - the approximate upper limit for the hearing of a young, physically fit human - it shouldn't be too surprising that other mammals use ultrasound for purposes like communication. Or, in the case of shrews, for actual echolocation.

There has been significant laboratory research on the use of ultrasound by mice and rats since at least the 1970s, but it has also become clear that they are far from the only rodents to make sounds beyond our hearing range. Last year, I talked about the potential use of ultrasound for sexual seduction among hamsters (and, to be honest, didn't reach much of a conclusion) and we also know that, for example, baby voles call to their mothers ultrasonically if they become separated.

In the case of squirrels, though, we know rather less, and much of what we do know applies to various kinds of ground squirrel. As recently as 2013, however, it was discovered that flying squirrels also use ultrasound, presumably for social communication. Indeed, the sounds were quite complex and varied, not mere repetitive squeaks, implying that they might impart rather more information that one might think at first glance.

Sunday, 7 August 2016

Bovines: The Largest Living Antelopes

Common eland (male)
Over the last few months I have looked at the various species of cow-like bovine, including such creatures as yak, bison, and water buffalo. But we've known, since at least the 1950s, that there are also a number of other animals that are more closely related to cattle than they are to other kinds of bovid. Although the choice of terminology is ultimately arbitrary, these are commonly considered to be members of the subfamily Bovinae, and thus can also be described as "bovines".

They are not, however, physically very cow-like, and so are instead described by the more generic term "antelope" - which really just means "any bovid that's not obviously some kind of cow, sheep, or goat". The great majority of antelopes are therefore not "bovines" in any sense, belonging to their own distinct subfamilies. The majority of those that are are commonly referred to as spiral-horned antelopes. While all bovines are said to have some degree of spiral growth pattern to their horns, it's only in these antelopes that it's really obvious, with multiple turns of the spiral clearly visible to the observer.

Saturday, 30 July 2016

Pliocene (Pt 12): From Rabbits to Rhinos

Around three million years ago, as the Pliocene began to draw to a close, North and South America collided, the island chain that had previously stretched between them rising to become the Isthmus of Panama, and much of the rest of southern Central America besides. With a solid land bridge in place, land animals from both continents were finally free to mingle, merging two faunas that had, until then, been quite distinct.

The North "won" the resulting battle of competition, in that far more creatures successfully moved south than travelled in the opposite direction. These were, on the whole, creatures we're familiar with across the Northern Hemisphere, because the proximity of North America to Asia had already led to some blurring between the animal groups there. So, it's as a result of this, the Great American Interchange, that South America has foxes, deer, cats (most obviously jaguars and ocelots), mice, rats, weasels, otters, and rabbits.

Not only that, but some of the animals that headed south later died out in their northern homeland, so that today, we think of them as being uniquely or primarily "South American". These animals include the llamas and the tapirs, and, to a lesser extent, the peccaries or javelinas, which still survive in Mexico and the American south.

Sunday, 24 July 2016

The Echidna's Incredible Expanding Testicles

The echidna is a pretty strange mammal. Most notably, it is the only mammal other than the platypus that lays eggs. I've discussed in an earlier post why that doesn't disqualify it from being a mammal, but it is undeniably unusual. It's not even the only odd thing about echidnas, since they can also sense electricity through their snout, and the males have a four-headed penis.

I'm not making this up.

There are, in fact, four different species of echidna. The one most people are likely familiar with, though, is the short-beaked echidna (Tachyglossus aculeatus), on the grounds that it's the only one found in Australia. (The others, if you're wondering, live in New Guinea). In fact, they're found pretty much across the whole of Australia, albeit generally in open woodland or rainforest, rather than true desert. Even so, that's a fairly broad range of habitat types and variations in climate, and their behaviour does change somewhat across the continent.

Sunday, 17 July 2016

Bovines: Mini-Buffaloes

Anoa (probably lowland species)
One of the themes that we see played out from time to time in evolution is that of insular dwarfism. Here, a population of some large animal is trapped on an island or (less commonly) some other isolated locale from which they cannot easily escape. Faced with a limited food and other resources, over sufficiently large periods of time, they become smaller, making the best of whatever there is. (There is also a related phenomenon of insular gigantism, whereby really small creatures become larger, likely because they no longer need to hide from predators that happen to absent on their island).

Today, there are no tiny elephants or rhinos, but bovines - where the males of some species can weigh upwards of a ton - are a different matter. At least two, and probably three, species of living bovine are examples of exactly this principle in action.

The reason that I'm vague about the numbers here is that there is still some dispute about the nature of the anoa. There are usually regarded as being two species: the lowland anoa (Bubalus depressicornis), and the mountain anoa (Bubalus quarlesi). But not everyone agrees that the two are distinct. The first formal suggestion that they might be separate species was made by Dutch scientist Pieter Ouwens, better known for being the first scientist to describe the komodo dragon. That was back in 1910, and at least as late as the 1960s, there was still general agreement that the two forms were physically distinct, and that they likely favoured different terrain.

Sunday, 10 July 2016

Fossilised Squirrel Brains

The fossils of mammals, and, indeed, other vertebrates, tend to consist largely of bones. That's not an absolute rule, of course, and occasionally other parts do fossilise, and there are also remains of things like footprints and poo. But, generally speaking, it's much harder to get an idea of the soft anatomy of a long-extinct mammal than it is of what its skeleton looked like.

There are many soft organs that we'd really like to understand the evolution of, but, while we can make inferences on other grounds, direct fossil evidence is always likely to fall short for most of them. The brain, however, is something of an exception, and this is perhaps fortunate, given the importance we tend to attach to it.

This is not to say, of course, that finding direct fossil evidence of brain structures in long gone mammals is particularly easy. But the brain sits inside the skull, and is fairly tightly wrapped within it. Which means that if we can get some idea of the shape of the hollow bit on the inside of a skull, we've got a pretty good idea of the shape and size of the brain it once housed. This has, in fact, been done for a number of fossil mammals, but, generally only of large ones. For smaller mammals, such as rodents, the evidence is much more patchy.

Sunday, 3 July 2016

The Importance of Monkey Grandmothers

Humans are almost unique among mammals in experiencing menopause a long time before their actual death. That is, they continue living for an extended period after they cease to be able to have children and pass their genes on to the next generation. Evolutionarily speaking, one might think, there is no longer any point to them; their task is done. But, obviously, that's not the case, as we can see from the importance of grandmothers and other female elders in, for example, tribal societies. For example, their greater knowledge of the world, and the ability to share in the childcare of their descendants, can mean that the latter have a better chance of survival.

Examples of this effect among other mammals are much less common. At the extreme, some mothers simply drop dead as soon as they have raised even a single batch of children to adulthood, but even among the majority of species, it's being a mother, not a grandmother, that's really important. Perhaps the best known exception is among elephants. Here, the leader of a family group is typically the oldest living female, who helps the herd through her knowledge of the outside world (where watering holes may be found in the dry season, for example), experience of predators, and a lifetime's worth of social knowledge.

Sunday, 26 June 2016

Bats v. Hawks

Bat hawk
There are not many animals that eat bats. Or, at least, that's often been the received wisdom. Bats only come out at night, fly through the air, where it's difficult to catch them, and many spend the day sheltering in caves that are difficult to access, and that rapidly become filled with so much bat poo that not much else is willing to venture within. But they don't all live in caves, they aren't the only things that come out at night, and, anyway, there's just an awful lot of them, so surely something must, in fact, eat them?

And, of course, the answer is "yes". In fact, there are actually quite a lot of animals that eat bats from time to time. In Brazil, for instance, snakes, especially tree-dwelling constrictors, have been reported to prey on bats. So do other vertebrates, from fish to mammals, and even a few invertebrates, such as, yes, really - giant centipedes. But, considering all that flying they do, it's perhaps unsurprising that the main predators of bats are, in fact, birds. And, among the birds, it's doubtless also not a great shock to discover that owls are the primary culprits.

For instance, it has been estimated that in Britain, at least 11% of all bat deaths (and probably more than that) are caused by birds. Around three quarters of those attacks are by tawny owls (Strix aluco), and 90% of all predation incidents on bats in Britain are due to owls of some kind. With 5% of predation incidents having nothing to do with birds at all, it nonetheless follows that a further 5% must be due to birds that aren't owls... and, of course, this is just Britain, where (for example) tree-roosting bats are quite rare.

Sunday, 19 June 2016

Bovines: Will the Real Buffaloes Please Stand Up?

African buffalo
Outside of North America, the term "buffalo" refers not to the bison, but to two (or more) species of bovine native to Africa and Asia. In the wild, by far the more common of the two is the African buffalo (Syncerus caffer), which has the distinction of being the only non-domesticated species of truly cow-like bovine that isn't even slightly endangered.

African buffalo are very numerous, and found across wide swathes of Africa south of the Sahara. This includes a fair number of different habitats, and African buffalo vary not just in their habits and preferences, but in their physical appearance, across that range. They were first described scientifically by Swedish naturalist Anders Sparrman in 1779, based on an animal found at Algoa Bay, near present-day Port Elizabeth in South Africa. Given the association with that general part of the world, the alternative name of "Cape buffalo" is often used for the animal, although that seems a little restrictive for something so widespread to me.

At any rate, over the next century and a half, scientists racked up descriptions of an impressive number of subspecies - by 1913, at least 21 were recognised. In the hundred years since, that number has steadily declined as it has become clear just how tiny the differences between some of them were. Even now, the question isn't entirely settled. There is agreement that there at least three subspecies, but there might be more, and it has been also been argued that some of them are genetically distinct enough to be full species in their own right.

Sunday, 12 June 2016

Pliocene (Pt 11): A Profusion of Pigs

Probably the most numerous large mammals in Africa today are the antelopes, of which there are a great many species. In this respect, the Pliocene was not much different, with antelopes providing a large part of the diet of the various carnivores that lived before the Ice Ages, from lions and hyenas to sabretooth cats. However, the mix of antelope species was different then that it is now, not least because of the generally lusher environment that existed in Africa during the earlier part of the epoch.

Even so, most of the antelopes of the day were related to species that we would recognise today. For example, even at the very beginning of the epoch, around 5 million years ago, South Africa boasted a gazelle similar in size to a modern springbok. Indeed, springboks proper appeared around 3 million years ago in the same general locality, where they were represented by at least two extinct species until one of them (probably Antidorcas recki) evolved into the iconic modern animal.

The gazelles of the early Pliocene were likely different in their habits from the modern sort, being more adapted to woodland than open plains, but, moreover, they were not as common, comparatively speaking, as they are now. Instead, it appears that, at least in East Africa, a group known as the spiral-horned antelopes (about which I will have a lot to say elsewhere on this blog over the coming months) were rather more numerous.

Sunday, 5 June 2016

Heading South for Supper

Birds are by no means the only animals to make lengthy annual migrations. While most annual migrations by mammals are of the relatively short-distance kind - moving down the side of a mountain as winter approaches, say - some can be surprisingly impressive. To travel a truly long distance, walking is generally not your best bet, so most mammals that do so are not the kind that would travel overland. Given their parallels with birds, perhaps the most obvious mammalian examples are bats. While most sleep away the insect-free winter in a cave, some bats do travel long distances. As just one example, straw-coloured fruit bats (Eidolon helvum) have been reported to travel up to 2,500 km between Congo-Kinshasa and Zambia in search of the best ripe fruit in any given season.

Which isn't up there with the most impressive of the migrating birds, by any means, but isn't exactly a short hop, either. And, if you can't fly, swimming is another option. Indeed, one of the mammalian species that migrates the furthest is the humpback whale (Megaptera novaeangliae), with migrations of up to 10,000 km having been reported.

Humpback whales are, in fact, found just about everywhere on Earth that's covered by seawater, excepting only the Arctic Ocean and some smaller seas with restricted physical access (such as the Mediterranean). Different populations, therefore, can migrate along very different routes. But the pattern is generally the same: they spend the summer in cold waters, where they stuff themselves with krill, and then head towards warmer climes as the winter sets in, giving birth and raising their young over the summer before returning to their feeding grounds.

Saturday, 28 May 2016

Memory Tests for Mouse Lemurs

The ability to learn and remember things is a vital ability for just about any animal, albeit the sort of things that (say) monkeys are able to learn can be a good deal more complex than those flatworms can manage. There are, however, multiple different types of memory, rather than it being a single process that takes place in our brains and works the same way every time. There is the difference between short-term and long-term memory, for one thing (and there's actually more than two of those), but also between what are termed procedural and declarative memory.

Procedural memory is the ability to remember how to do something. Once you've learned whatever the task is, you don't need to think about it, it just comes automatically, like riding a bicycle. Exactly like riding a bicycle, in fact. Declarative memory, on the other hand, is the sort of thing you have to think about, such as remembering what happened to you the last time you were in a specific situation. If you're a human, this includes the ability to remember things like Vespertilio being a genus of bat (well, it is if you're me), but it also encompasses a much wider range of knowledge about the world and your own experiences in it.

Sunday, 22 May 2016

Bovines: Almost-Cows of Southeast Asia

Banteng female
So far, in my survey of the Bovinae subfamily, I've mostly looked at species that most Westerners are, if not personally familiar with, at least well aware of: domestic cattle, yak, and bison. The exception, perhaps, is the gaur, an unusually large (or, at least, tall) species of bovine native to Southeast Asia. The gaur, however, is not alone, for there are two other very closely related species that are native to the same general area.

The better known of these is likely the banteng (Bos javanicus), an animal that was once found from eastern India to southern China, and across the whole of the Southeast Asian peninsula; there are even distinct subspecies on Borneo and Java. Today, the wild animal is extinct in India and Bangladesh, and found only in a few limited patches elsewhere. It has been formally listed as an endangered species since 1996, but the species as a whole is in much better shape than that would suggest... because this is another species that has been successfully domesticated.

The domesticated animals are known as Bali cattle, and they are in wide use across Indonesia and Southeast Asia. Over the years, a number have escaped from captivity, with the result that at least some feral populations are now found on a number of Indonesian islands that did not (so far as we can tell) ever host the genuinely wild form. More dramatically, British troops took some of them to the Northern Territory of Australia in 1849, but released them all just one year later when crop failure forced them to abandon their new settlement. The resulting feral animals are still there, and, while there are several thousand of them, all in Garig Gunak Barlu National Park near Darwin, since they are descended from just 20 imported animals, it's perhaps unsurprising that they are now highly inbred.

Sunday, 15 May 2016

Toothless Old Fossils

Artwork depicting extinct animals almost invariably shows them physically fit, unless they're actively engaged in some life-or-death battle. They're usually either adults in the prime of life, or still juveniles (often newborn). And this is actually quite reasonable, since few animals get to live to an old age out in the wild. Most will, after all, be eaten before then, and if they have any serious illness or crippling injury, they're not going to last long. Senescence, the gradual decline of biological function associated with becoming elderly, is not something we see much in the wild, for all that it's common in humans and domestic animals.

Which isn't to say that we don't see it at all, especially in very large animals that have few, if any, natural predators once they reach adulthood. The same must also have been true in the distant past, and it's reasonable to assume that at least some fossils, at least of the larger animals, belong to elderly individuals. It isn't, however, necessarily going to be all that obvious, especially if the skeleton is incomplete in the first place. Nonetheless, a recent report does describe a jawbone that the authors believe belonged to an elderly animal, and, if they're right, this offers some unusual insights into the creature in question.

Sunday, 8 May 2016

Friends and Family Among the Degus

A great many mammals are solitary. They spend most of their adult lives more or less alone, only meeting up with others of their kind in order to mate. Apart from a mother with her young, the extent of their social lives outside the mating season is just driving off rivals. But, of course, there are a great many that are sociable amongst themselves, forming herds, packs, or other associations. For a herbivore this often provides safety in numbers, while a pack-hunting predator may have the ability to take down larger prey than it otherwise could.

How does social living get started, in evolutionary terms? Perhaps the simplest way is that children simply fail to leave their mother, creating a fairly permanent family group. According to one theory, such groups are likely to become particularly stable if there are not enough resources around (for whatever reason) to allow the children to wander off and have young of their own. In these situations, the theory proposes that the older children hang around in order to help their close kin, such as younger siblings, and thus have at least some chance of passing their genes on to the next generation.

Sunday, 1 May 2016

The Largest Weasel Ever?

The weasel family were the first group of mammals that I decided to spend a year describing in detail on this blog, back in 2011-12. I concluded the series with a look at their fossil history, stating, among other things, that the fossil genus Enhydrodion "may" have been the largest member of the family to have lived. This, however, relies on guesswork relating the size of the body of the animal to its skull, which is all we have in any completeness. But there are, in fact a number of other fossil members of the family with even larger skulls, so a lot rests on their exact bodily proportions, which are often a mystery.

Such examples include the giant wolverine Plesiogulo (for which we have not only the skull, but, just possibly, the penis bone), the giant hypercarnivorous honey badger Eomellivora, and the relatively long-legged Ekorus, whose relationship to other mustelids is unclear. But, according to a new analysis, the largest mustelid skull known belongs to an animal called Megalictis ferox.

Of course, calling Megalictis a "weasel" is a bit of a stretch. The weasel family is very diverse, including such animals as otters, badgers, and wolverines, as well as more obvious examples such as polecats and stoats. So, yes, it's really only a weasel in the same sense that a badger is... and that's assuming it's a member of the weasel family at all. So, let's start with that - what is this animal, and is it really a mustelid?

Sunday, 24 April 2016

Bovines: Bison bison bison, the Bison

American bison
The only bovine native to the Americas is the bison (Bison bison). Indeed, it is one of only five species of bovid that fit that description - the other four all being members of the goat subfamily. To give at least some variety, however, there are two generally recognised subspecies of American bison, one of which, following the standard rules for naming subspecies, necessarily goes by the wonderfully tautonymous trinomial Bison bison bison.

This, in fact, is the plains bison, which was once found across pretty much the whole of what is now the contiguous United States, leaving aside only the Pacific and Atlantic coasts and the arid deserts of the Southwest; they also lived in far northern Mexico and up as far as central Alberta. The other subspecies, commonly known as the wood bison (Bison bison athabascae) is native to north-western Canada and to Alaska. Physically, it's slightly larger than its southern relative, which means that, in the absence of American rhinos, elephants, and so on, it is, in fact, the largest living, land-dwelling animal of any kind native to the Americas.

Because bison are, indeed, pretty big. A fully grown male can be anything up to 195 cm (6' 6") tall at the shoulder, and can weigh as much as a tonne (2,200 lbs). Females are, admittedly, quite a bit smaller, although at a maximum of about 180 cm (6') and 550 kg (1,200 lbs) they're still pretty big - and closer in size to the males than, say, those of yak. The horns are also about the same size in both sexes, although (relative to the rest of the animal) fairly small in comparison to those of most other bovines.

Sunday, 17 April 2016

Pliocene (Pt 10): Before There Were Zebras

At the dawn of the Pliocene, Africa, like Europe, was a much wetter place than it is today. As a result, it was also much greener, a place of lusher vegetation, and the animals that fed on it. While that likely made little difference to the heart of the Congo jungle and to the more tropical reaches of West Africa, which are about as green as they're going to get, elsewhere the changes would have be obvious to any putative time traveller.

The biggest difference was likely in the north, where the even the very heart of what is now the Sahara Desert was likely covered in arid scrubland - hardly hospitable, but a significant improvement over baking hot dune-fields. By one estimate, moist savannah and open woodland stretched as far north as 21°, covering what are now countries like Chad, Sudan, and Mauritania. Further east, Somalia would also have been covered by woodland, rather than its current dry grasslands, and, at the opposite end of the continent, there may have been small forests in what are now the Namib Desert and the Kalahari.

It didn't last, of course. Around 3 million years ago, as the world fell irrevocably into the long autumn of the late Pliocene, Africa became not only cooler, but drier. And, if the generally cooler climate did not make too much difference to a continent sitting on the equator, the loss of rain certainly did. It's at this time that the Sahara, and the other deserts we are familiar with today, began to form, and the wildlife had to either adapt to that fact, or die. What was good news for voles in Europe, promoting the tougher grasses on which they thrive, was bad news further south, where the grass gave way to open sand.

Sunday, 10 April 2016

The Last Seals of the Mediterranean

There are eighteen recognised species of "true" seal (that is, as opposed to fur seals, which are actually more closely related to sea lions). Three of these species are currently listed as endangered under the most widely recognised international standard for such things, the IUCN Red List. Compared with some other groups of animals - rhinos being a particularly obvious example - this isn't really all that bad. But it could, of course, be rather better.

One of the endangered seal species is the Caspian seal, found only in the isolated and land-locked sea of the same name. The other two are monk seals, with one species each in the Mediterranean and off the coast of Hawaii. Quite how two such closely related species ended up on opposite sides of the globe is something I've discussed in an earlier post, but for today, the key point is that there used to be three species of monk seal, and that the other one went extinct around 1952.

Given this, the threat to the two remaining species is surely far from hypothetical. There are thought to be a little over a thousand Hawaiian monk seals alive today, but, as confirmed in a recent species review, the most endangered seal species of all is the Mediterranean monk seal (Monachus monachus) - the only seal species to live in the sea for which it is named.

Sunday, 3 April 2016

Bovines: The Other Domesticated Species

Domestic yak
The large physical size and herd mentality of bovines makes them ideal subjects for domestication, especially as beasts of burden. So much so in fact, that not only have true cattle been domesticated at least twice, but no less than four other species of bovine have also been domesticated on a wide scale since ancient times. (I am ignoring here the fact that bison, for example, have been farmed for their meat in recent decades, and am only considering "traditionally" domesticated animals). Unlike true cattle, the wild ancestors of these animals remain alive - all four of them in Asia.

One of the more familiar of these "other" domesticated bovines is the yak (Bos grunniens), which is descended from... well, the wild yak (Bos mutus). Today, wild yak are found only on the Tibetan Plateau, although in medieval times they may have lived much further north and west. One small population is known to cross the border into Ladakh in far northern India at certain times of the year, but they are otherwise extinct outside of China, having vanished from Nepal as recently as the 1990s.

Saturday, 26 March 2016

Dive of the Fossil Penguins

This is the post that will be current as of 1st April 2016. I will therefore be following my long-running annual tradition (that's "long-running" as in, "I've kept up this annual tradition for a whole year now") of posting about something that isn't a mammal, or even a synapsid.

When we think of 'birds' the ability to fly is surely one of the first things that come to mind. Indeed, the development of flight was surely one of - if not the - defining moments in early bird evolution. But, whereas bats have never given up that particular evolutionary innovation, flightless birds have evolved more than once. And, because we know that the very first birds could already fly, it follows that all flightless birds have ancestors that were perfectly capable of flight, but, for whatever reason, lost the ability.

Many, such as ostriches, did so to develop a fully land-based lifestyle, often becoming much larger in the process. But others swapped flight for diving ability. Of course, there are a great many diving birds that are still able to fly, but sometimes there is an advantage in really specialising in diving to the point that flight is no longer an option. This has, in fact, happened more than once in the course of avian evolution, but the only flightless diving birds we have now are the penguins, propelling themselves through the water with wings shaped like flippers.

Sunday, 20 March 2016

CSI Atlantic Ocean

Lungworm in a Guiana dolphin (H&E)
Here in the UK, there have been a number of news stories about whale strandings over the past couple of months. A number of sperm whales wandered into the relatively shallow waters of the North Sea, which they do not normally visit, and became stranded at locations near Skegness in Lincolnshire and Hunstanton in Norfolk. A similar number stranded along the coast of Germany, and a few in the Netherlands and France. Unable to support their own bulk out of the water, they died of suffocation and cardiovascular collapse.

These sort of strandings are fortunately as rare as they are dramatic - part of the newsworthiness in this case was so many happened in such a short time. Fortunately, the great majority of cetacean "strandings" aren't like this at all. In most cases, the cetaceans are already dead, or nearly so, by the time they wash up. Furthermore, most of them are dolphins, simply because there are more dolphins than whales in the world, and they are also more likely to be swimming in coastal waters in the first place.

After all, every dolphin dies eventually, and the body has to go somewhere. Often, they sink, leading to the spectacular scavenger feeding frenzy of "whale fall" when a vast and blubbery carcass sinks into the depths of the deep ocean. But, especially if they happen to die close to the coast, there's every chance that the body will float for long enough to eventually wash up somewhere. It happens every now and then to humans washed overboard from ships, so, when you think about it, it's unsurprising that it happens to at least some dolphins, too.

Sunday, 13 March 2016

The Size of Dead Rodents

When it comes to fossil animals, there is an undeniable fascination for the largest and most dramatic of species. It's part of why dinosaurs are so much more popular in the public mind than fossil mammals. Even among dinosaurs, while creatures such as Coelophysis have their fans, there are surely many more people who would name the likes of Tyrannosaurus, Brontosaurus, or Triceratops as their "favourite dinosaur". When it comes to fossil mammals, it's the mammoths and the sabretooth cats that hold the public imagination, and we also like to hear of giant bears or mighty prehistoric rhinos.

There's nothing wrong with that, and I'd have to confess to that bias myself. (I mean, come on, who doesn't love sabretooths?) Indeed, it seems that for much of Earth's history, the largest land animals were indeed larger than their counterparts today. But, at any given point in time, the small animals always outnumber the large ones. Today, over two thirds of known mammal species are either rodents, bats, moles, or shrews, and, while the details might have changed, it seems plausible that the majority of mammals in the past were at least roughly in that size range.

Sunday, 6 March 2016

Stressed Out Squirrels

Southern flying squirrel
Stress is, it seems, an inevitable part of life. You just can't get away from it altogether, and that applies to animals as much as it does to humans. True, they tend to get stressed out about different things, not being able to ponder the future, although it's surely true that if we were about to be attacked by, say, a man-eating tiger, we'd probably find that as stressful as mice find the presence of cats.

In fact, stress is such an integral part of life that, at a biological level, it works in more or less the same way in all vertebrates. Stress results in the release of stress hormones, of which the most important is cortisol. In mammals, this is produced in the adrenal cortex, the outer part of the adrenal glands, which sit on top of the kidneys, and produce a whole range of different hormones of which cortisol is only one. So basic is this that all non-fish vertebrates have adrenal glands of some sort, although which bits of them make the cortisol (and, in some cases, how many there are) does vary between different groups. Even fish, which usually don't have adrenal glands as such, do have the relevant sorts of tissue somewhere in the general vicinity of the kidneys, so that they too can make cortisol. It really is that universal.

Sunday, 28 February 2016

Bovines: How Cows Were Domesticated

Taurine bull
Cattle (Bos taurus) are among the most familiar of herbivorous domestic animals. According to recent estimates, there are well over a billion of them on the planet today, found almost anywhere that humans practice agriculture. In the west, we are familiar with them as a source of beef or milk, but, in many parts of the world, they are still used primarily as draft animals ("oxen"). Indeed, they are important enough that Christopher Columbus first brought them to America in 1493, on only his second voyage to the New World.

But one unusual thing about cattle is that there is no living wild form of the animal. There are still wolves and wildcats, wild goats, wild sheep, and wild boars... but there are no wild cattle. They're not unique in this respect, to be sure, and there are a few populations of feral cattle around the world (that is animals living in the wild whose ancestors were domesticated), but it's a fairly exclusive club nonetheless. And, obviously, it wasn't always the case.

Sunday, 21 February 2016

Pliocene (Pt 9): Coyotes, Cats, and Spectacled Bears

A modern spectacled bear
When it comes to the extinct mammalian predators of North America, few are more famous than the sabretooth cat Smilodon, with the dire wolf likely coming a close second. But both of these animals lived during the Ice Ages, and, of course, with all those tasty horses, deer, and so forth wandering the steppe-lands of Pliocene North America, there were plenty of carnivores there before the Ice Ages began. Indeed, scary though Smilodon undoubtedly was, unless you're the kind of person that enjoys wrestling hungry tigers in the modern world, many of these others were probably quite dangerous enough.

But not, it has to be said, all of them - at least, from a human perspective. There were, as you might expect, many small carnivores in North America at the time, including badgers, weasels, skunks, raccoons and early wolverines and otters. While we can't know the details of their coat colours, it's quite likely that many of these creatures would have looked not too different from their modern relatives and possibly would have been hard to tell apart from them on casual inspection.

Sunday, 14 February 2016

March of the Beavers

When most people think of "rodents", they most likely think of rats or mice. This is fair enough, as the great majority of rodent species pretty much fit that description. But there are, of course, many others. Voles, hamsters, gerbils, and so on are probably fairly obvious, and somebody once asked me if squirrels were "members of the vermin family", by which I assume they meant "rodents" - which they certainly are. One suspects, however, that beavers might come fairly low on most people's list.

Having said which, it's probably not so surprising when you think about it. They do, after all, have huge gnawing teeth that look like those of rats (and which, indeed, help define the rodents as a group). Granted, they are pretty enormous as rodents go, and bulky with flat, paddle-shaped tails, but rodents they are, with animals like gophers and kangaroo rats among their closest relatives.

The beaver family, ignoring the extinct forms, contains a grand total of two species, both of which are found in Europe. One of them is the animal familiar to Americans (Castor canadensis). Descended from a population that originally lived in Wyoming and Canada, these were shipped across to Finland in 1937, and subsequently spread across the country, crossing the eastern border into Russia in 1952. A year later, some of them were moved again, this time to Austria, and in the 1970s, some were shipped all the way to eastern Siberia. All of these populations survive, although attempts to introduce the animals to France, Ukraine, and Belarus all ultimately failed.

Sunday, 7 February 2016

Sea Lion Bachelor Pads

Spot the male
As I mentioned just a few weeks ago, male mammals are generally larger than female ones, although there are some notable exceptions. This is particularly the case where males have to compete for access to females, and there are few cases where this is more obvious than among seals and sea lions.

Sea lions and "true" (or "earless") seals belong to different, if closely related, families, but their reproductive strategy is much the same. In both cases, they spend most of their lives at seal, but they can't give birth there without their pups drowning. The majority of species breed once every year, with the females coming ashore, first to give birth, and then, almost immediately after, to get pregnant again before returning to the sea.

The precise details vary from species to species, but the South American sea lion (Otaria flavescens *) is a typical example. In December each year (that is to say, in early summer, this being the Southern Hemisphere), males haul themselves out onto beaches and fight one another for the best spots. Naturally, the largest and most aggressive males win, with the smaller and younger individuals forced out, to either wait another year, or to make daring raids when the larger ones aren't looking.

Saturday, 30 January 2016

Bovids and Bovines - What Makes a Cow?

The cattle family, Bovidae, is the largest and most diverse of the various families of big herbivorous mammals, with only the deer family coming close to it in number of species. The majority of its members are antelopes of one kind or another, and it also includes goats and sheep, as well, of course, as the cattle themselves. Given the number of species within it, and the fact that a bison, say, has a number of obvious differences from a gazelle, there have been various attempts down the years to group its members into subfamilies or other smaller groupings.

However, opinions have differed as to quite how this should be done. How many significant sub-groups are there, which of them are deserving of the rank of "subfamily", and which animals go with which? Even with modern techniques for analysing genetics and coming up with computer-generated metrics of relatedness, the answers to these questions are not entirely clear. Partly that's because the first two questions at least are essentially arbitrary, and partly because we haven't really got enough samples from some of the more obscure species to really nail the family tree down. There could be anything up to sixteen subfamilies, or just two, or somewhere in between.

Sunday, 24 January 2016

How Fossil Rodents Met Their Doom

Tritemnodon, another early hyaenodontid
from Wyoming
A large part of palaeontology consists, as you might expect, of looking in detail at the fossils that are dug up. This can tell us a lot about the animal and how it lived. By analysing the shape of the teeth, we can get some clue as to what sort of things the animal ate, and from the shape and proportions of the limbs and other body parts we may be able to infer other details of the lifestyle. If it's a carnivore, for example, did it chase its prey, or pounce on it from hiding and overwhelm it with sheer physical force? If the former, it should have long, relatively slender limbs suitable for running, if the latter, we'd expect powerful limbs with attachments for strong muscles.

When it comes to fossil mammals, teeth are often the best guide. For one thing, being small, and made of material even harder than bone, they are more likely to be preserved, even if the entire rest of animal is missing. For another, for most mammals, the precise shape of the cheek teeth (molars and premolars) is highly distinctive, giving us clues as to how one particular species is related to others. Even if we did find, say, an isolated rib, it might be difficult to tell what it once belonged to, and it probably wouldn't tell you much about the animal in question even if you could - beyond, perhaps, some clue as to its size.