Oligocene (Pt 17): Dawn of the Kangaroos

Ekaltadeta

Kangaroos are perhaps the single most iconic Australian mammals. As marsupials, we tend to think of them as lost relics of an earlier evolutionary period, and, indeed, they have been around for a long time. Of course, they have been evolving during that time, rather than standing still, but if we had a time machine, we could go back millions of years into Australia's past, and still find animals that were, more or less, kangaroos. But, obviously, there is a limit.

Exactly how far back that limit is partly depends on how kangaroo-like you want your kangaroos to be. But even then, there are some gaps in our knowledge that don't have direct counterparts on other continents. The obvious place to start is with the fossil record, and, here, at least, we can provide a clear answer. The oldest known fossil kangaroos date to around 28 million years ago, towards the end of the Oligocene.

Oligocene (Pt 16): The First Monkeys in South America

A modern South American monkey

Much like the rodents, the presence of monkeys in South America has long been a puzzle. We know that monkeys evolved in Africa and that the monkeys still living in the Old World share a common ancestor distinct from, but related to, the common ancestor of the American sort. Genetic evidence shows that the split between the two lineages, which must have happened in Africa, happened a very long time ago. At some point then, early monkeys from what we now call the 'New World' group must have crossed the Atlantic, likely rafting on a floating patch of vegetation.

The Atlantic was narrower then than it was now, and ocean currents were different, but it's still a remarkable feat. It may also have been a lucky escape, since the African relatives of this first American migrant died out not long after, perhaps outcompeted by the ancestors of today's langurs, baboons, macaques, and apes. In South America, however, its descendants got almost free rein, diversifying into the five families we have today.

Prehistoric Mammal Discoveries 2024

Zalamdalestes

I have reached the end of another year and that means it's time for what has become a tradition on this blog over the last eight years: a look back at some of the discoveries about fossil mammals made in 2024 that didn't make into the regular posts. As usual, this will be a quick whistle-stop tour of mammalian palaeontology, hopefully focusing on some of the more interesting findings. Like any field of science, it has not been standing still.

Large Herbivores

Woolly mammoths (Mammuthus primigenius) are among the best-known of all prehistorical mammals to the general public and, aided by the fact that some lived recently enough to be preserved in permafrost, they are also amongst the best-studied. But there is still more to learn about the details of their lives and habits. A study published this year looked at the detailed isotopic composition of a fossil mammoth that had died about 12,000 BC in Alaska, showing that she was female, and had migrated over 1000 km (600 miles) during her lifetime, having originally been born in the Yukon. The area in which she died was popular with mammoths, but also with humans - she may have died peacefully, but the presence of people where mammoths congregated may not be a coincidence.

Scratching the Surface

The environment of the Earth is shaped, not just by sunlight, wind, and the geography of mountains and seas, but by the living organisms living on it. This process has been described as "ecosystem engineering", and it inevitably affects far more than the organism that's doing the modification - sometimes negatively, but often in ways that are generally beneficial.

In its broadest sense, ecosystem engineering can include changes to a habitat caused by the mere existence of an organism. The existence of multiple trees in close proximity creates a forest, which is a very different sort of environment to, say, a grassland, and this obviously has huge effects on what the resulting habitat is like for other organisms. One could also think here of coral reefs or the nutrient-rich hotspots created by a whale carcass sinking into the depths.

Giant Kangaroos: Were They Utterly Hop-less?

Most people have a clear image of what a kangaroo is: a large herbivorous animal that carries its young in a pouch and that moves by hopping about on its hind legs. There are three living species of true kangaroo, and this description does, indeed, accurately fit all of them. However, the kangaroo family, or Macropodidae, is much larger than this, with a total of 63 species, most of which can generically be described as "wallabies". 

There are also several fossil species known, stretching back to the late Oligocene, over 25 million years ago. Having only skeletal remains, and often partial ones at that, while we know that they had sufficient similarities to be placed in the same family and their teeth indicate they were herbivorous, what about the other two features: pouches and hopping? 

Wombats Moving Home

There comes a time in the life of many young mammals when they have to leave home. There are at least two major reasons for this. Firstly, any given place only has so many resources, so unless your parents die as soon as they've finished raising you (unusual among mammals, although not unheard of), at some point, you have to move elsewhere or there won't be enough food for both of you. Secondly, if the whole family stays together in one place, you'll never meet new sexual partners, forcing you to mate with your siblings - and we all know where that leads.

Understanding how and when animals disperse from their place of birth can be important for conservation as well as, on a broader scale, how new species and subspecies evolve and adapt. Nor is it necessarily something that only applies to young approaching maturity, since older animals may also choose to move from one place to another and often for similar reasons - competition or a lack of suitable mates. Whether a given animal chooses to move home, and how far they travel to do so, can be influenced by several different factors. 

Prehistoric Mammal Discoveries 2023

Potamotherium

It's the last post of the year for 2023, and that means it's time once again to take a brief look at discoveries from the last year in the world of fossil mammals that didn't make it into this blog. Because, while dinosaurs are undoubtedly popular, the study of prehistoric mammals is also a major field, aided by that, being (mostly) relatively recent they tend to be more numerous and better preserved. Of course, everyone's heard of woolly mammoths and sabretooth cats but there's plenty more out there and, if I'm going to zip through them at speed today, I'm also going to try and cover as wide a range as possible. So, let's get going...

Hammer-Toothed Snail Eaters

As is true of mammals more generally, the majority of Australian marsupial species are herbivorous, including such familiar animals as kangaroos, wombats, koalas, and possums. (The latter, of course, are not to be confused with the American opossums, which are omnivorous and not very closely related to their Australian namesakes). Most, but not all, of those that are not belong to a single order, the dasyuromorphs, sometimes called the "carnivorous marsupials" for this reason.

Although they represent almost a third of non-American marsupial species, dasyuromorphs are far less diverse than their herbivorous counterparts, with all but one of the living species belonging to a single family, the dasyurids. Although the most famous example of the dasyurids is probably the Tasmanian devil, which eats comparatively large prey, most of the other species are small shrew-like animals feeding on insects. Alongside them, we can place the numbat and the extinct thylacine ("Tasmanian tiger" or "wolf") both of which are odd enough to be placed in families of their own.

Dunnarts in the Sandhills

It's a recurring theme of this blog, especially notable in last year's series on Old World leaf monkeys, that a great many mammalian species are threatened in some way. Population numbers of many species are declining, to the point that their continued existence is in doubt, often due to human encroachment on their habitat, but also due to the habitat itself changing as climate change continues. In this context, the quest of zoologists to understand how mammals (and other animals) behave is not just one of intellectual curiosity but can be of direct benefit to the creatures themselves.

For example, it is useful to conservation efforts to understand not only where a given species lives, and the habitat requirements it may have, but how it makes use of that environment. (Obviously, there's more to it than this, for example, how different species in the same area interact with one another but we'll stick with this one point for today). What particular features of the habitat are important to it? How much land does it need? How is its population distributed across the area? 

Miocene (Pt 35): Crash Bandicoot and the Giant Platypus

Nimbacinus

When we think of marsupials, the animal that's probably most likely to come to mind first is the kangaroo, likely followed by the koala. Both of these animals, along with wombats and possums, belong to the largest order of marsupials, technically referred to as the diprotodonts - a term that literally means "two front teeth" on account of the enlarged, vaguely rodent-like incisors that characterise the family. These are used to clip at vegetation, since the group is overwhelmingly herbivorous.

This was less true in the Miocene, and that's because of the existence of marsupial lions. Or, more accurately, of thylacoleonids, members of the "marsupial lion" family, since the truly lion-sized animal best known by that name didn't live until much later. The group originated towards the end of the previous epoch, when some herbivorous, probably wombat-like, animal switched to a more meaty diet, its front teeth becoming blade-like in order to cut into flesh. They seem to have prospered during the Miocene, with three different genera currently recognised.

Miocene (Pt 30): Horned Armadillos and Marsupial Dogs

Borhyaena

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

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

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:

Miniature Marsupial Lions

Thylacoleo carnifex

The largest carnivorous marsupial alive today is the Tasmanian devil (Sarcophilus harisii). Noticeably smaller than a European badger, it's still almost twice the weight of the next nearest contender for that title, or, indeed, of the omnivorous Virginia opossum so well-known to Americans. Most other living predatory marsupials can more accurately be described as "insectivores", due to their small size.

Unsurprisingly, this wasn't always so. Most famously, perhaps, there was the thylacine or Tasmanian wolf, which officially went extinct in 1936. There were also the "marsupial sabretooths" of South America, which died out during the Pliocene about three million years ago. However, these are no longer thought to technically be marsupials in the sense of being descended from the last common ancestor of the living species, even if they were definitely in that branch of the mammalian family tree.

Prehistoric Mammal Discoveries of 2019

Nehalaennia, an 8 million-year-old rorqual
from the Netherlands, first described this year

As the year - and decade - approach their inevitable conclusion, it's time again to look back at a few palaeontological findings of 2019 that didn't, for whatever reason, make it into the regular Synapsida posts. As always, there is no theme to this list, just a sample of what seemed interesting linked only by when it happened to be published.

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.

The Many Kinds of Living Marsupial

Ringtail possum
Because not every animal in Australia wants to kill you

This blog probably wouldn't exist were it not for the fact that there are a great many different kinds of mammal alive in the world today. Most of these are placental mammals, giving birth to (relatively) fully formed young that have been nourished by a placenta in their mother's womb. A significant minority, however, are marsupials, which belong to a separate evolutionary line that split from the placentals long before the dinosaurs died out.

Marsupials are diverse animals, in many cases, paralleling their placental counterparts in some key aspects of their anatomy or behaviour. True, they are not quite as diverse as their placental kin - there are no marsupials bats or dolphins, for instance. There are around 350 known living species of marsupial, commonly grouped into 19 "families", and, while is this undeniably small compared with the 5,000+ species and 120 or so families of placentals, it's hardly insignificant.

What is a Marsupial?

A possum

In America, the word "possum" is usually used to describe a moderately-sized, somewhat rat-like, animal that has grey fur, sometimes pretends to be dead, and has far too many teeth for any self-respecting land-based mammal. Officially, this creature is an "opossum", and more specifically, the Virginia opossum (Didelphis virginiana). The word comes from the language of the Powhatan people of Virginia, and has been in use in English since at least the 17th century.

Over on the other side of the world, in Australia, the word "possum" is, however, used to refer to an entirely different animal. These are nocturnal, tree-dwelling creatures, typically with large eyes and long tails, and the majority of the seventy or so species are herbivorous. Early settlers, who had probably only vaguely heard of the American animal, nonetheless decided to give it the same name. Like the Americans, over time they confused "opossum" with "a possum", and shortened the word. Unlike the Americans, their shortened word became not merely colloquial, but the one formally used in zoological texts.

Do Kangaroos Chew the Cud?

Mammals that eat a lot of grass, or other relatively low-quality vegetation, have to process their food thoroughly to extract the maximum amount of nutrition. I've previously discussed how this works in some detail, but, in general, there are two approaches. In "fore-gut fermenters", the stomach is divided into multiple chambers, allowing the animal to ferment its food, then bring the solid parts back up to the mouth to re-chew ("chewing the cud"), before sending it back to finish the job. This is the system found in cows, deer, camels, and many other animals, collectively known as "ruminants".

The second approach is to place the fermentation chamber behind the stomach, down in the colon. This is less efficient, but quicker, and is the arrangement found in horses, rhinos, and a number of other animals. Rabbits are also "hind-gut fermenters" of this sort, but take the additional step of re-eating the fermented food once it passes out of their back end for the first time.

I mentioned in passing in my previous post that kangaroos are fore-gut fermenters, but that they are not ruminants, and have a slightly different system. Today, I'm going to explain what it is that they do do. (Much of what follows applies equally to wallabies, and, to a lesser extent, rat-kangaroos).

Pliocene (Pt 15): Life on the Australian Grasslands

Kolopsis, a diprotodontid

At the dawn of the Pliocene, Australia was a relatively green continent, with plenty of rich, tropical and subtropical, vegetation. That changed as millions of years passed, with the continent becoming steadily drier and the grasslands and semi-desert of the Outback came into being. This was, of course, bad news for many of the animals that had lived there in the wetter past, many of which went extinct, but it also saw a noticeable increase in the number of grazing animals, for which wider grasslands were clearly a boon.

Elsewhere in the world, this sort of thing was benefiting animals such as horses, goats, and antelopes. But Australia was different. It wasn't, of course, the only island continent of the day, but it was the oldest by some margin, having separated from its neighbours long before South America split from Antarctica, or before animals stopped crossing between Eurasia and North America (even ignoring the Ice Age crossings of the Bering land bridge, which were, at this point, still in the future).

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.