Pliocene (Pt 16): The Pliocene Oceans

Bohaskaia

Over the last two and a half years, I have talked about a range of mammal species found across the Pliocene world. So far, I have only looked at the continents, and the various animals that lived on land. But the Pliocene seas were, of course, equally teeming with animal life. Much of this naturally consisted of either fish (most famously the giant "megalodon" shark) or invertebrates of various kinds. Sea turtles also existed, including some quite large ones, but, in keeping with the scope of this blog, I'm going  to focus on the mammals.

While we often tend to think that prehistoric animals tended to be larger than those alive today, this, was however, rather less true of whales, which have grown more or less steadily in size over the course of their evolution, perhaps in part to make it increasingly difficult for anything else to eat them. So, for example, the Pliocene killer whale (Orcinus citoniensis) was around 4 metres (12 feet) in length, barely more than half that of the modern species - although still quite impressive on a human scale.

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.

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

Macrauchenia

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.

Pliocene (Pt 12): From Rabbits to Rhinos

Toxodon

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.

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.

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.

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.

Pliocene (Pt 8): Long-Tusked Elephants and Giant Camels

Cuvieronius

America today is not a place you associate with herds of wild elephants. Go back just a few tens of thousands of years, though, and it would have been quite a different story. The "elephants" of the time were, of course, mammoths, and they were accompanied by mastodons, animals that were not actually members of the elephant family, but which, from a modern perspective, have a pretty strong resemblance to them.

Mammoths first entered North America during the early Pleistocene, not long before the Ice Ages proper got going. They were, in their origin, Asian animals, but the mastodons were a different matter. Mastodons were already in North America when the mammoths arrived, and they had been there for a very long time indeed. For millions of years, America really was a place with herds of well... things that looked a lot like elephants, at any rate.

The creature that the American mammoths would have encountered was the American mastodon (Mammut americanum), an animal that first appeared close to the end of the Pliocene. But this was the last survivor of a much longer lineage, and there had been many more kinds of American proboscidean that lived before it, often alongside one another. In fact, only a minority of them were really mastodons, including the immediate predecessors of the American mastodon, such as Mammut raki, and the somewhat older Zygolophodon. The latter also lived in the Old World, and was likely the first mastodon to reach North America, shortly before the dawn of the Pliocene. Nonetheless, one of the best skulls we have of the animal was unearthed in California, and later mastodons of the continent are likely descended from something much like them.

Pliocene (Pt 7): Home, Home on the Steppe

Mylohyus

The beginning of the Pliocene epoch in North America was not marked by any great cataclysmic event, such as happened in Europe at that time. Nonetheless, while we're not far enough back that North America is unrecognisable, or in a different place, or anything like that, there would have been clear differences if we could see it from space.

Perhaps the most obvious difference would be that the Great Lakes didn't exist yet, since they were carved out by the advancing glaciers of the Ice Ages - which have yet to happen. With sea levels higher, Florida (then, as now, not a place known for its mountain ranges) is largely underwater, and there were probably many other changes around the coast, too.

Arguably the most important difference, however, is further south. Mexico is not so different, at least in its general outline, but beyond that things start to change. Depending on the exact point within the Pliocene we're talking about, you could perhaps have walked as far as Nicaragua without getting your feet wet. Beyond that, however, the Central American peninsula tapers to a point, and where Costa Rica and Panama should be, there is nothing but a chain of tropical islands, a southern counterpoint to the much larger chain of the Caribbean further north.

Pliocene (Pt 6): Attack of the Hyenas

Pachycrocuta brevirostris

Pliocene Europe was a continent as yet untouched by human hand - although, as I've noted, not of non-human primates. One might think that, in the absence of humans, sabretooth cats were probably the thing that other animals had to fear the most. There's probably a lot of truth in that, but they were far from the only carnivores in Europe at the time, and some of them were pretty fearsome.

On the other hand, there were also much smaller carnivores, too. At the bottom of the scale, weasels, badgers, otters, and martens already existed on the continent, and may have been quite common in the forests of the time. Foxes also survived the Zanclean Flood, and have continued living in Europe, right through the Ice Ages, up to the present day. In fact, Pliocene foxes would have looked remarkably similar to those of today, and are generally placed within the same genus, Vulpes.

Similarly, the largest carnivores of the European Pliocene would also have looked familiar. These were the bears, dominated by the gianr Agriotherium, which may have been slightly larger than a modern polar bear. Another woodland creature, it had perhaps been more common in the previous epoch, but survived throughout almost the whole of the Pliocene, dying out not long before the Ice Ages began in earnest.

Pliocene (Pt 5): The Last Sabretooths in Europe

Homotherium

Apologies for the absence of a post last week. This was due to personal circumstances that meant I just couldn't bring myself to write. Normal service has now been resumed.

Six million years ago, there were many different kinds of sabretooth cat in Europe. That, however, all came to an end with the Zanclean Flood and the dawn of the Pliocene epoch. It's not that they literally drowned in the flood, of course - almost by definition, most of the parts of Europe we know today were above where the flood waters stopped. But Europe changed in the aftermath of the flood, seeing, over an admittedly long period of time to human eyes, a change in the nature of the herbivores that lived there. And, when the herbivores change, so do the animals that have to eat them.

Most of the European sabretooths died out in the very earliest part of the Pliocene. The one exception was the "terror cat" Dinofelis, which became perhaps the dominant large predator in Europe for the next million years or so. However, once the climate took a turn for the worse, and the long prelude to the Ice Ages began around three million years ago, Dinofelis followed its relatives into extinction.

Pliocene (Pt 4): Before the Mammoths

Anancus arvernensis

One of the markers for the end of the Pliocene is the "Mammoth-Horse Event" when the slide into autumnal temperatures that had defined the later part of the epoch reached the point that significant quantities of ice began to build up in the Northern Hemisphere - notably in Greenland, where it still remains today. In Europe, this cooler weather brought an end to many of the more northerly forests, replacing them with open tundra-like grassland. Many aspects of the local fauna didn't change all that much, although they likely edged a bit further south.

But the arrival of the grasslands did herald the appearance of single-toed horses, and of mammoths - albeit not the woolly ones that most people immediately think of. Mammoths are perhaps the poster-child for the Ice Ages, but Europe was, of course, not devoid of such large animals before their coming.

Pliocene (Pt 3): Of Gazelles and Three-toed Horses

Hipparion

The Zanclean Flood may have been a catastrophe of epic proportions, but, so long as you were above where the flood waters eventually stopped, Europe at the dawn of the Pliocene was a fairly pleasant place. The weather was warmer than today, and, apparently wetter too, which might not be what time-travelling tourists would be looking for, but was certainly good news for the plants that were actually there. Where places like Spain, Italy, and Greece are today dominated by... well... "Mediterranean" scrubland, back then they would have been considerably greener. And what's good for plants is good for herbivores.

Especially when it comes to cloven-hoofed animals, many of these would have been animals that would have been, at least in general terms, familiar to us. Not necessarily familiar to us from Europe, though, since, in addition to pigs, bovines, and deer, there were also a number of antelopes. These were mostly members of the gazelle subfamily, although there were others, including some, for example, related to the modern sable antelope. The gazelles included Hispanodorcas, a small and slender antelope with slightly twisting horns, with fossils found in southern Spain. However, some were even closer to the gazelles of today, to the point that, if, like most people, you'd be pressed to tell the difference between a Dorcas gazelle and a Speke's gazelle today (or at least, to know which one was which), you'd probably not have identified these as anything different, either - although at least some of them were smaller than any living species, which might have helped.

Pliocene (Pt 2): Survivors of the Zanclean Flood

For verily, I shall inherit the continent!

As I noted last time, officially, the dawn of the Pliocene - the autumnal epoch immediately prior to the Ice Ages of the Pleistocene - is marked by one of many changes in Earth's magnetic polarity. However, that particular event wasn't picked at random; there really were visible changes at the time. And, in Europe, none were more significant than the Zanclean Flood.

To understand what this is, though, we have to turn to the latter part of the preceding epoch, the Miocene, and take a look at the Messinian Salinity Crisis. The Miocene was much longer than the two epochs that followed, long enough that, over the course of it, the continents moved about a fair bit. Towards the end of the epoch, then, moving northwards, Africa hit Europe.

Due to the shape of the respective continents, however, this didn't result in the sort of massive mountain building that we see in present day Tibet (or, at least, it hasn't yet - the continents are still moving). But it did have a dramatic effect nonetheless. Crucially, the continents didn't just nudge up against one another in the east, creating what is now the Sinai, but also in the west, creating a land bridge between modern Spain and Morocco.

The Mediterranean Sea became land-locked. The Mediterranean climate of the day was even hotter and drier than it is now, and, free from any connection to the Atlantic and Indian Oceans, the sea began to evaporate. Over the course of hundreds of thousands of years, the sea level dropped. Not just a little bit, but by as much as three miles.

Age of Mammals: The Pliocene (Pt 1)

I suspect that when most members of the public think of prehistoric animals after the time of the dinosaurs, they think of the Pleistocene, the time of the Ice Ages. This was a time of bitter cold, the time of cave men, mammoths, and Smilodon cats. Even among scientists, it's easily the most researched of the various bygone epochs that make up the Age of Mammals, not least because it's the one closest in time to our own, and therefore the easiest to study.

But there are five other epochs that precede the Pleistocene within the Age of Mammals, and, compared with most of them, it isn't even very long. Heck, it isn't even 5% of the total. As it happens, though, the epoch that immediately preceded the Ice Ages, the Pliocene, isn't much longer. If we imagine, as we're often invited to, the entire history of the Earth as a single year, the Pliocene is, very roughly, the period between 2 and 7 p.m. on the evening of the 31st December. That's not exactly a large chunk.

On the other hand, on a human scale, the Pliocene is vast; the long autumn that leads from the summer of the Miocene into the freezing cold of the great ice sheets that follow. When I first discussed the Pleistocene, I used the example of a TV documentary that whizzes through the whole of history. In fact, it takes one minute to cover each decade of time. So the entire history of the world since the outbreak of World War I is covered in just the final ten minutes. Your life so far is, I can assume with some confidence, covered in even less time than that.