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. 

The Sexy Face-Masks of Lekking Bats

The mating behaviour of mammals is, unsurprisingly, highly varied across different groups and species. We would hardly expect the behaviour of dolphins to resemble that of reindeer, for example, or hedgehogs to resemble cheetahs. Reproductive information is one of the key biological factors we tend to look at when describing a species, even if it isn't quite as easy to evaluate as, say, diet or habitat. (Or anatomy, of course, which doesn't even necessarily require the animal to be alive). Look at almost any write-up of a mammal species in an encyclopedia, and there'll be something on reproduction - assuming we know it.

But, for a great many mammal species, we don't. This may be because it's rare, or difficult to observe in the wild, or perhaps that it's a newly discovered species that we can reasonably assume isn't that different from close relatives we already knew about. But, at least when it comes to reproductive behaviour, one of the biggest gaps in our knowledge concerns the bats.

Prehistoric Mammal Discoveries of 2020

The largest known Oligocene whale was
moved into the new genus Ankylorhiza
this year

Well, that year was... different. Fortunately, it didn't stop me posting and, indeed, a cancelled summer break meant that you got one more post than anticipated you lucky people, you. But as 2020 finally passes into the history books where it can bloody well stay, it's time for the end-of-year roundup of paleontological discoveries that didn't make the regular blog. As always, no theme, just a random assortment of journal papers that may, for all I know, be thoroughly contradicted by this time next year. But this is a collection of things that some scientist, somewhere, thinks that they demonstrated in 2020:

Fossil Cats (That Aren't Sabretooths)

Acinonyx pardinensis

The cat family is traditionally divided into two subfamilies: the "purring cats", which are mostly small, and the "roaring cats" which are all medium to large in size. When most people think of fossil species, however, the first ones to pop into their minds are almost certainly the sabretooths, such as Smilodon. These belonged to a third subfamily (and whether they could roar or not depends on fragile bones and soft tissues that haven't survived) that left no modern descendants, dying out towards the end of the Ice Ages.

The sabretooth cats represent an early branch in cat evolution, perhaps splitting off at some point during the Early Miocene, over 20 million years ago. But this means that the cats we are familiar with must have existed - in some form - for equally long, leaving their own fossil history. If you wound back the evolutionary clock on a domestic cat, or even a tiger, you wouldn't find a sabretooth or anything that looked much like one. Exactly what you would find isn't something we can know with certainty, but we do know of a number of fossil species of non-sabretooth cat that at least give us some idea.

The Mammal That Lived Like a Woodpecker

Plesiadapis

The time since the extinction of the non-avian dinosaurs is traditionally divided into seven "epochs". Unsurprisingly, the more recent the epoch, the more familiar the animals that inhabited the Earth at the time. In my current long-running series on the animals of the Miocene (the fourth of these epochs, and also the second-longest) I have been able to talk about a number of mammals that can at least be placed into groups we understand. Horses may have had three toes, elephants may have had four tusks, and so forth, but at least we can tell, without any great difficulty, that they are, in fact, horses and elephants.

As you'd probably expect, this gets harder the further back you go. Firstly, even animals belonging to familiar groups are getting further away from their present-day forms. There comes a point where whales still walked on land, for instance. Secondly, the further we go back, the more animals we find that didn't leave any modern descendants, and, indeed, weren't even closely related to anything that did (Smilodon, for instance, has no living descendants, but it's still pretty obviously a cat). That can sometimes make it harder to say where such animals fit into the mammalian family tree or, perhaps more importantly, how they lived and behaved.

Miocene (Pt 23): Giraffes Become Tall, Hippos Stay Dry, and Antelopes... Get Eaten

Palaeotragus, a short-necked giraffe

About half-way through the Late Miocene, around 8 million years ago, worldwide temperatures began to drop significantly, and even tropical Africa did not escape the effects. In its case, this didn't lead to cold and barren steppelands, and, indeed, the world may still have been slightly warmer than it is today, but there is evidence of the expansion of grasses across many parts of the continent. Perhaps enhanced by the closure of the Mediterranean Sea during the Messinian Salinity Crisis and disruption of the monsoons, North Africa also became much drier than before, although whether the Sahara as we know it today dates back quite that far remains controversial; there is some evidence of sand dunes that far back, but also of numerous rivers crossing the region.

These changes in climate also affected the animal life on the continent, to the benefit of some and the detriment of others. Pigs are omnivorous animals, and one might expect them to have survived such changes relatively unscathed. In a sense, this is true, since they remained common on the continent, but the nature of particular species living there did change.

The Best Place to Den

Winter is a difficult time for many animals at high latitudes. Food is scarce, and the cold climate itself is a problem. Although many mammals do manage to keep going through the winter, others migrate to warmer climes, while many of those that don't hibernate instead. While this is by no means easy, for animals that can manage it, it allows them to preserve their energy, surviving off body fat without the need to search for food.

There has, historically, been some dispute as to whether bears truly hibernate or not. This is because the sort of undoubted hibernation practised by, say, bats, involves an almost total shutting down of normal metabolic functions with the animal effectively becoming cold-blooded for the duration. Bears do not do this; while they are asleep through the winter, their body temperature drops from a normal level of 37°C (99°F) to a low of 33°C (91°F). Now, this is not insignificant, since a human with a body temperature that low would be suffering from clinical hypothermia and in fairly urgent need of medical treatment. But still, you're not going to be so cold that dew literally starts forming on you, as happens with bats.