Miocene (Pt 37): The Miocene Oceans

Xiphiacetus

Given their extreme adaptations to a life at sea, it should not be surprising that whales and dolphins have a long evolutionary history. Even at the dawn of the Miocene, when seals were at best, only very recent arrivals, and may still have been semi-aquatic, like otters, the cetaceans were already well-established. A time-travelling whale-watching expedition at almost any point during the Miocene would likely have been just as rewarding as one today and, especially so far as one would have been able to see them above the waves, the animals you would have been spotting would not have looked all that different.

At a more detailed anatomical scale, that would have been less true and many of the creatures would not have been as closely related to the modern forms as one might have supposed. Today, the largest number of cetacean species belong to the "true" or "oceanic" dolphin family, including not only all of the sea-going dolphins but some larger animals such as killer whales. But in the Miocene, true dolphins seem to have been comparatively rare and we know of very few fossils predating the subsequent, Pliocene, epoch.

Miocene (Pt 36): Dawn of the Seals

Allodesmus

In this series so far, I have covered the mammalian wildlife of the Miocene continent by continent, showing how the diversity of animals then was just as great as it is now. But there is a group of mammals that a time traveller to the period would have been able to observe along the coasts of those continents - especially during their breeding season - that I have not yet mentioned.

Today, the seals are divided into two subfamilies (I have reviewed all living species of seal here): the phocine or "northern" seals, which live in the Northern Hemisphere, and the monachine or "southern" seals, which are primarily found in the Southern Hemisphere, but do include three living species in the north. 

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 34): The First Kangaroos in Australia

Ekaltadeta

During the Miocene, Australia was further south than it is today. However, it seems that the generally warmer climate of the early part of the epoch more than compensated for this, since we know that there were already coral reefs off the coasts of the main continent and also of New Zealand, which is far too cold for such things today. At the dawn of the epoch, the continent seems to have been largely covered by open woodland but as the world warmed in the Middle Miocene, and Australia edged northward, it became not only hotter, but wetter, until tropical and semi-tropical rainforests became the norm. It was only in the Late Miocene, around 10 million years or so ago, that the climate started drying again, especially in the interior, and the dense jungle began to die away, leading the way for the formation of today's Outback in the following, Pliocene epoch - although, even at the end of the Miocene, the coasts were more heavily forested than most of them are today.

Miocene (Pt 33): Killer Armadillos and Far-travelling Raccoons

Lycopsis

As the Miocene epoch drew towards its conclusion, the island continent of South America drew steadily closer to its northern counterpart. The gap would not be fully bridged by land until a few million years later at the end of the following, Pliocene, epoch but, when it did, many of the peculiar mammals of the southern continent would die out, albeit in many cases it was the subsequent Ice Ages and/or the arrival of humans that truly finished them off. One group that survived the experience, and that is still around today, is that of the armadillos.

Even so, armadillos were more diverse in the Late Miocene than they are today. Probably the most distinctive were the glyptodonts, which had solid, often domed, shells without the flexible bands seen in living armadillos. As the sweltering heat of the Middle Miocene faded towards temperatures closer to those we see today, grasslands began to extend across much of the southern part of the continent, and the glyptodonts adapted to it, switching towards an even more heavily grass-based diet than before. The resulting group of what we might loosely call "advanced glyptodonts" was the one that would later briefly cross over into the north and includes the most famous examples. In addition to certain features of their shell, they were distinguished by having teeth especially suited for chewing, with the high crowns suitable for grinding up grass and other tough vegetation.

Miocene (Pt 32): Time of the Sea-Sloths

Pronothrotherium

In the absence of the sorts of herbivore more familiar to us today - and already current in the Northern Hemisphere of the day - the large herbivores of Late Miocene South America were nonetheless varied. Many took up habits similar to those of their northern counterparts, so that, at a brief glance, they would not necessarily have appeared so odd to a passing time traveller. 

The mesotheres are a possible case in point. They were a group of notoungulates, one of the two orders of native hoofed mammal that had survived into the Late Miocene along with the litopterns. Earlier in the Miocene, they had perhaps looked even less remarkable, digging herbivores of a similar size and shape to wombats. But as the epoch wore on, they gradually increased in size, while still retaining the adaptations to digging, which they would likely have used to get at tasty roots, and possibly for constructing burrows in which to live.

Miocene (Pt 31): Terror Mice and the First Howler Monkeys

Phoberomys

As the heat of the Middle Miocene gave way to the more moderate temperatures of the Late Miocene, grasslands grew across much of the Northern Hemisphere. In South America, however, the changes were, perhaps, less significant due, in part to its more equatorial position. Nonetheless, even aside from the general worldwide cooling trend, the South American climate was changing as the Andes continued to rise, affecting weather patterns across the continent. It was also continuing to edge closer to North America, so that, towards the end of the epoch, it became possible for a few animals to make the crossing using the islands of what is now Central America as stepping stones.

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. 

Miocene (Pt 29): Fake Elephants and Otter-Shaped Herbivores

Nesodon

At the dawn of the Miocene, South America was home to no fewer than three orders of moderate to large hoofed herbivore, compared with the two it has today (one containing the deer and llamas, the other including the tapirs). There is, of course, a degree of arbitrariness in what gets designated an 'order' as opposed to some other ranking. But nonetheless, these animals were distinctive, related to the two orders of ungulate we have today, but different from both of them. 

Two of these South American groups would outlast the Miocene, only dying out relatively recently. These were the litopterns and the notoungulates, both of which bore most of their weight on the third toe of each foot, and which may, indeed, be related to the group containing the tapirs, horses, and rhinos, which does the same today.

Miocene (Pt 28): Miniature Super-horses and the Dawn of the Guinea Pigs

Thoatherium

For most of the Age of Mammals, South America was an island continent, separated from its northern counterpart by a wide sea. Even at the dawn of the Miocene, 23 million years ago, this isolation had already lasted for a long time, and the seas to the north were already a formidable barrier, with just a few islands where Central America is now. In some respects, the variation in climate across the continent was less extreme, especially because the Andes were not so high as they are today and so cast less of a rain shadow. Even so, there was enough variety that many different kinds of animals lived across its great area.

Indeed, the long separation of the continent from the rest of the world meant that it had had plenty of time to develop its own native animals. Whereas, in most of the rest of the world, animals of broad types we would still recognise were already around (early cats, deer, elephants, and so on), most of the larger animals of Early Miocene South America would have been much harder to place, since most of their descendants died out long before the Ice Ages, let alone the present. 

Miocene (Pt 27): Rise of the Apes

Proconsul

From a human perspective, one of the most significant evolutionary developments of the Miocene epoch was the appearance of the first apes. Exactly when the group first arose isn't entirely clear, but it's either very early in the Miocene or very late in the preceding, Oligocene epoch. Part of the reason for the lack of clarity is, as so often, dispute as to where exactly the dividing line is between apes and monkeys when we go this far back in time. But there also seems to be some evidence that the earliest apes evolved in African jungle habitats, which weren't the best for forming fossils.

An example of this early confusion comes from Dendropithecus, from the Early Miocene of Kenya. Comparatively small, at only around 60 cm (2 feet) in length, and with arms that seem to be adapted to swinging from trees, when it was first named as a distinct genus in 1977, it was thought to be an ancestor of modern gibbons. Despite having a somewhat similar lifestyle and diet, this no longer thought to be likely, and one recent analysis places it as belonging to a very early branch in the ape family tree - just early enough that one could legitimately argue as to whether it really counts as an 'ape' or just a very close relative.

Miocene (Pt 26): Planet of the Monkeys

Victoriapithecus

The primates are one of the major mammalian orders alive today, with a great many species spread across three continents: Africa, Eurasia, and South America. They have an ancient history, and, even by the dawn of the Miocene, were already divided into the two main groups we have today: the prosimians and the anthropoid primates (most of which are monkeys, or 'simians').

It's probably fair to say that most scientific attention has been paid to the latter of those groups, but we do have a number of fossil prosimians from the Miocene. Madagascar, where most prosimian species are found today, was already an island, and had been since the time of the dinosaurs, but there are few known fossils of the relevant age there to tell us much about the early history of lemurs and their kin. Nonetheless, during the Miocene, prosimians were more widely spread than they are today. 

Miocene (Pt 25): The Large Clawed Cat-Cat and the First Dog in Africa

Lokotunjailurus

Today, the hyena family consists of just four species. All of them live in Africa and, generally speaking, they look somewhat like dogs. Three out of the four are scavengers, with powerful teeth adapted for cracking open bones to consume as much of a carcass as possible. The largest and fiercest of these is the spotted or "laughing" hyena, which is the one most people think of when the word "hyena" is mentioned, although there is more variety in the group than that. But even so, with just four species, it's not what you'd call a large taxonomic family.

During the Late Miocene, however, things were very different. It's hard to know the exact number of species that existed, even among the fossils we have, since some of the subtler differences may not be apparent from bones alone. But there were certainly plenty of genera, spread widely across Europe, Asia, and Africa. They were also more varied than today, and their success at the time may well have been due to the fact that actual dogs were still restricted to North America at the time, leaving the hyenas without direct competitors.

Miocene (Pt 24): Of True Elephants and Three-toed Horses

Stegotetrabelodon

The first horses entered Africa towards the end of the Middle Miocene, about 10 million years ago. These have commonly been assigned to the same genera, Hipparion and Hippotherium, as were found in Eurasia at the time, although the fine details of the exact relationships are unclear. Although the latter in particular seems to have been reasonably successful on the continent, a more significant immigration from an African perspective took place later on, around 8 million years ago as the drier climate heralded the start of the Late Miocene.

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.

Miocene (Pt 22): Last of the Creodonts

The largest predator in Africa today

The dominant mammalian carnivores in Africa today are the lions, hyenas, and leopards, with cheetahs and wild dogs also playing their role. The ancestors of all of these creatures first reached the continent from the north, shortly after it collided with Eurasia during the Early Miocene. For the most part, at the time, their ancestors were small, with hyenas, for example, being no larger than mongooses. But this does not mean that Early  Miocene Africa had no large predators at all.

For one thing, the cats, hyenas, and so forth, were not the only carnivorous mammals to have made the crossing from Asia. The animals known as bear-dogs, or more technically, amphicyonids, are far better known from Europe, Asia, and North America, but they did reach Africa, too. 

Miocene (Pt 21): Mongooses and More

A modern mongoose

When Africa, moving north, collided with Asia around 19 million years ago, a number of hoofed animals, and other large herbivores, headed south to colonise the continent. Naturally, where herbivores go, predators follow, so an influx of carnivorous animals occurred at around the same time.

Until this time, Africa had been an island continent, separated from the larger northern landmasses and lacked many of the kinds of carnivore we are familiar with today. It had, for example, no cats, dogs, or bears, or even such quintessentially "African" animals as hyenas. All of these, and others besides, belong to the group of mammals known as "carnivorans", which essentially includes all large land-dwelling mammalian carnivores today, apart from the Tasmanian devil. They had evolved in the north, and the new land bridge gave them their first chance to reach the more southerly continent.

Miocene (Pt 20): Unicorn-Pigs and the First Hippos

Prodeinotherium

Pigs seem to have been another example of animals crossing over from Asia when that continent collided with Africa around 17 million years ago. The oldest fossil pigs in Africa date from about that time and are represented by Kenyasus from Kenya and Nguruwe from Namibia and South Africa. These were relatively small, short-snouted pigs with a primitive appearance similar to that seen in their presumed Asian ancestors.

Because of these primitive features, determining exactly where they fit in the pig family tree isn't a simple matter, but they are often placed with a group called the kubanochoerines. Assuming this is correct (and it's far from settled) they must have evolved fairly rapidly into much larger and more distinctive animals. The best-known member of the group is the giant "unicorn-pig" Kubanochoerus, which lived in China during the Late Miocene. This was an exceptionally large, long-legged animal, perhaps standing 120 cm (4 feet) high at the shoulder and - even more dramatically - sporting a long pointed horn that projected from the centre of its forehead.

Miocene (Pt 19): When Rhinos and Giraffes Went South

Prolibytherium

At the dawn of the Miocene, 23 million years ago, Africa was a very different place than it is today. This was as much due to simple geography as anything else. For one thing, the Sahara Desert didn't exist yet - even the most extreme estimates suggest that it didn't begin to appear until the Late Miocene, and it may well have not have formed until at least the Pliocene around 4-5 million years ago. Before this time, much of the continent was probably covered in warm, damp, forests interspersed with patches of more open woodland and scrub.

More significantly, perhaps, Africa was still an island continent, separated from Eurasia by a body of water called the Tethys Seaway. It had been like this, isolated from the rest of the world, for millions of years, during which time it had developed its own unique animal life, quite different from that elsewhere. At the time, the same was true of South America (and it still is for Australia), but that continent retained its unusual animals for much longer, not contacting the north until as recently as 2.5 million years ago, shortly before the first of the Ice Ages. When that did eventually happen, it led to the Great American Interchange, which set the scene for much of the American fauna we see today.

Miocene (Pt 18): Return of the Cats

Barbourofelis

For much of the Miocene, bears were represented in North America by the single genus Ursavus. This was relatively primitive, and small by the standards of modern bears, although still easily identifiable as such. It seems to have left no local descendants, but, around 7 or 8 million years ago, it was joined - and eventually replaced - by new arrivals from Asia.

The best known of these were Indarctos and Agriotherium, bears that were widespread across the Northern Hemisphere of the time, and common enough in both Asia and Europe. Indarctos was the smaller of the two, roughly the size of a black bear, and with what was probably a similarly omnivorous diet. It was likely more closely related to pandas than to other modern bears, and died out as the Miocene ended.