Requiem for a Dolphin

Dolphins are social animals, living in pods and engaging in what seems to be fairly sophisticated communication. It's likely that such behaviour is part of the reason for their success, with well over 30 species spread across the world's oceans... and that's excluding porpoises, and some other "dolphin-like" animals outside the dolphin family proper.

Sociability involves a number of different traits and behaviours, but one that's known to exist in cetaceans and relatively little else, other than primates, is what's technically known as epimeletic behaviour. This is, in essence, the act of helping other members of your species when they are in trouble, typically due to an injury of some kind. (For what it's worth, this compares with etepimeletic behaviour, which is acting in such a way as to make it easier for others to care for you).

Gerbil versus Rattlesnake

Sidewinder

Deserts are harsh environments, and living in them poses animals a number of problems, not least of which are daytime heat and an absence of water. In order to survive in such a place, animals need to evolve suitable adaptations - extremely efficient kidneys to reduce water loss are one such example.

But the thing about deserts is that, while there are some geographic differences between them, the challenges of living in one are at least broadly similar regardless of which desert it happens to be. And while, say, the world's seas are all connected, the deserts aren't. So animals, including mammals, have had to evolve means of surviving in them several times over, re-developing the necessary features each time they encounter a new one.

Prehistoric Mammal Discoveries of 2018

Gordodon,
a new non-mammalian synapsid described this year

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

Beginnings and Endings

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

Miocene (Pt 11): Horses on the Grasslands

Daeodon

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

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

Not the Pig Family: Fossil Peccaries and More

Mylohyus

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

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

Twilight of the Almost-Primates

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

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

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

How Baby Bats Learn to Fly

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

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