Miocene Apes: A Radiation, and a Pruning

1 From Spain to Yunnan

Between about twelve and nine million years ago, you could have traveled east from Spain all the way to Yunnan, using today's place names, and passed through one place after another where apes lived. There were apes near Barcelona, in northern Hungary, near Ankara, the capital of Turkey, and in the woods along ancient river channels in northern Pakistan. Keep going east to Yunnan: apes there too. Turn south into Africa, and there were apes in Kenya as well.

In those days their range reached as far north as southern Germany and northern Hungary, roughly forty-eight degrees north, the latitude of present-day Munich and Vienna.

Today's map is different. Here we focus on nonhuman apes: Southeast Asian gibbons, orangutans on Borneo and Sumatra, and equatorial African gorillas and chimpanzees. They depend largely on forests, including mountain forests and woodland–grassland mosaics, not exclusively rainforests. Humans are apes too in biological classification; this essay leaves our branch outside its main focus.

There is another contrast, less widely known. For much of the Miocene, apes were more diverse than monkeys in the Old World. Today the balance is reversed: monkey species outnumber ape species several times over. This concerns taxonomic richness in the known record, especially the Early and Middle Miocene, not a census of individual animals.

Ten million years ago, Europe was one of the richest places on Earth for ape fossils. Today it has not a single wild ape. This essay is about what happened between those two moments.

First, a couple of terms. What separates an ape from a monkey? The simplest answer is the tail: apes have none; monkeys do. Everyday Chinese happens to get this distinction right. The gibbon is called an “ape,” the macaque a “monkey.”

But tails rarely fossilize. In the fossil record, teeth are usually more useful. An ape's lower molars have five cusps, with grooves between them arranged in a Y. A monkey's molars have two transverse ridges. Even a single lower molar, then, can often tell us whether we are looking at an ape or a monkey. The two-ridged comparison specifically concerns typical Old World monkey molars; one tooth is not an infallible test across all monkeys and apes.

The other term is “genus,” plural “genera.” Lions, tigers, and leopards are three different species within the same genus. A genus sits one rank above a species, gathering several closely related species together. We will keep returning to counts of genera and species in this essay. These are the two levels we mean.

Let us set out the timescale too. The Miocene is an epoch on the geological calendar, running from about twenty-three million to about 5.3 million years ago. It lasted nearly eighteen million years and is usually divided into three parts: early, middle, and late.

When it began, forty-three million years had already passed since the extinction of the dinosaurs. How long is eighteen million years? A little over five million years separate the end of the Miocene from today. The Miocene itself lasted more than three times that long.

We can sketch the Miocene story of apes in four sentences, then enlarge each part in the sections that follow.

By about twenty million years ago, several kinds of ape already lived in East Africa. Around sixteen million years ago, they entered Eurasia. Between about twelve and ten million years ago, they were found all the way from Spain to Yunnan. Then, beginning around ten million years ago, their range contracted region by region, until by about six million years ago the Eurasian fossil record contained apes at only a handful of sites, with some of the latest in Yunnan. This follows selected Miocene fossil lineages, not the disappearance of all Eurasian apes. Orangutans and gibbons alone rule out that reading.

In 2023, researchers counted all the securely identified Miocene apes, one by one: thirty-five genera, fifty-six species. Lions, tigers, and leopards together occupy just one genus. Here there were thirty-five. For another point of reference, the entire living cat family, from house cats to tigers, contains only a dozen or so genera.

The list is still changing. Since 2023, one new genus has been named in each of Germany, Turkey, and Egypt, while another genus has been removed altogether. Section 5 will look at how those names arrive, and how they leave.

Why give this interval an essay of its own? Because it offers one of the clearest examples in this series of a group flourishing and then being drastically cut back. At the end of the Permian, in Episode 14, and the end of the Cretaceous, in Episode 18, large numbers of groups were wiped out together within a geologically brief interval.

Nothing of that sort happened to the Miocene apes. There was no impact, no single concentrated episode of massive eruptions. Their contraction unfolded over millions of years, one region after another.

And this interval is close enough to the present, with records dense enough in several regions, for us to see the range drawing inward piece by piece.

Episode 20 explored the radiation of mammals after the dinosaurs, asking whether the “vacant places” were filled in turn. The Miocene apes are a much later, smaller chapter within that larger story. But their chapter has a second half: after the radiation came a pruning we can actually follow.

“Pruning” is a gardener's word. A tree fills out with branches; the cut branches fall to the ground. A few years later, no one remembers where they grew. Our task here is to pick those fallen branches up, one by one, and ask where they once belonged and how they came to be cut away.

We will follow the story forward in time. First, what the earliest apes looked like; then, how they spread and how many ways of life they developed at their height. After that, how the pruning happened. Finally, what unfillable gaps the pruned branches left behind.

2 The Earliest Apes

Lake Victoria is Africa's largest lake. On its eastern, Kenyan side lie two islands, Rusinga and Mfangano.

Forest animals are unlikely candidates for fossilization. A body falls onto a damp forest floor, and its bones soon decay in the slightly acidic soil, unless river sediment, lake mud, volcanic ash, or something similar buries them quickly. Rusinga happened to provide just such conditions. Between about twenty and seventeen million years ago, material from nearby volcanic eruptions and deposits along the lakeshore rapidly sealed away large numbers of bones.

The two islands consequently preserve an enormous collection of early ape fossils: skulls, teeth, and many bones of the trunk and limbs. How enormous? Large enough that, as recently as 2025, researchers could still go through its canines, jaws, and skulls one by one and reassign them.

In the late 1940s, Rusinga yielded an almost complete ape skull. For the first time, someone could see the whole face of a Miocene ape, rather than a few teeth and a piece of jaw.

The most abundant apes in this collection belong to Ekembo. For years they had been filed under a more famous genus, Proconsul, a name that for much of the twentieth century was practically shorthand for “early Miocene ape.” A new diagnosis in 2015 moved most of the Rusinga material into the newly established Ekembo, abruptly narrowing the scope of the old name.

Ekembo had no tail, just like living apes. Beyond that, its body was very different. Its lower back was long and flexible, its rib cage narrow and deep. Its shoulders, wrists, and hands showed little in the way of special modifications for hanging.

Assemble those bones and you get an animal that walked on top of branches. All four limbs rested on the branch, palms against the bark, the body held roughly horizontal as it moved forward step by step. Many monkeys still travel this way today.

The early apes had no tails, but they did not hang from the trees. Losing a tail and swinging beneath a branch are two separate things.

This matters because the word “ape” now brings almost exactly that second picture to mind: long arms, an upright body, an animal hanging beneath a branch. But those features did not arrive together with the loss of the tail. As the next few sections will show, they appeared separately, in different sequences and different combinations in different apes.

The length of the lower back is one of the most useful clues. Monkeys usually have six or seven lumbar vertebrae; living great apes have only three or four. A short lower back steadies the trunk, making it well suited to upright climbing and hanging. A long one allows the trunk to flex and extend, bending and releasing like a spring during running: useful for traveling on all fours along the tops of branches.

So if we could return to Rusinga twenty million years ago, we would not see apes swinging through the trees. We would see animals stepping briskly along substantial branches. From a distance they would look more like monkeys. Only when we came closer would we notice the missing tail.

At Nachola in northern Kenya, an adult male from about fifteen million years ago left an almost complete skeleton, later excavated by a Japanese expedition. The ape was named Nacholapithecus. How rare is an almost complete skeleton? Among the thirty-plus Miocene genera, only a handful can supply one.

It had about six lumbar vertebrae: a long lower back. Many of its joints were still suited to walking on all fours above the branches. Yet its shoulders, elbows, and hands had undergone clear modifications that strengthened its grip and expanded the capabilities of its upper limbs. A long lower back, and hands that gripped better.

Nacholapithecus was not an unfinished product. It was a combination in its own right, one with no counterpart among living animals. If living animals were all we had to go on, no one could have designed that body from imagination.

About two million years before Nacholapithecus, other apes were already living in northern Kenya. One, found on the western shore of Lake Turkana, is known from a fairly complete skull. Another left fairly complete craniofacial remains and had very thick tooth enamel. It probably ate differently from the early apes with thinner enamel.

Early Miocene Africa had at least a dozen or so genera of apes like these, comprising eighteen to twenty-one species. Most were in East Africa, but some ranged north to Egypt. Moroto in Uganda also yielded a lumbar vertebra about twenty million years old, interpreted as a very early sign of an “upright body.” Its shape more closely resembles that of upright apes than that of their long-backed contemporaries. If this reading holds, an upright trunk had already appeared once among the earliest apes.

This was a genuine radiation. Within a few million years, on a single continent, a range of apes had appeared with different body sizes, diets, and anatomies.

Episode 20 used the image of a folding fan: the handle is a shared starting point, and the ribs open one by one, reaching in different directions. That is how the fan of apes opened in early Miocene Africa. It opened quite wide.

But almost all of them were still in Africa. What happened next was that they left.

3 From Africa to Eurasia

Between about seventeen and fifteen million years ago, Earth passed through the warmest part of the entire Miocene. Much of Europe was considerably warmer and wetter than it is today. Warmth and moisture allowed forests to reach farther north and deeper into the continent. And apes were forest animals.

By then, Africa and Eurasia were connected in the region of present-day Arabia and Turkey. The piece of crust carrying the Arabian Peninsula had drifted north and joined Eurasia not long before, closing off the ancient sea that had separated the two sides at that point.

A land route had opened. Apes were not its only travelers: many African mammals entered Eurasia around this time. This was when the apes left Africa too.

Fossils of the earliest arrivals in Eurasia come from central Europe and Turkey, from around sixteen million years ago. They consist mainly of teeth and jaws belonging to an ape called Griphopithecus. An ape of similar age has also been found on the Arabian Peninsula. It left only an upper jaw and a few teeth, but the location itself tells a story: it lies right along the corridor.

Over the next few million years, apes spread quite rapidly across Eurasia. Between about sixteen and twelve million years ago, their record appeared in succession in central Europe, Turkey, western Europe, South Asia, southwestern China, and farther south in northern Thailand.

Africa did not empty out simply because some apes had gone to Eurasia. Between about fifteen and thirteen million years ago, several thick-enameled apes still lived around Fort Ternan and Maboko in Kenya, and another is known from Namibia to the south. Middle Miocene Africa still had plenty of apes.

Across the Miocene as a whole, Eurasia had at least as many ape genera as Africa. Africa had roughly thirteen to sixteen; Europe alone had twelve to fifteen, before we even add western, southern, and eastern Asia, or Southeast Asia. That is a very different picture from the familiar one. Say “apes” and people think first of Africa. Yet in the latter half of the Miocene, Eurasia was a major home ground for apes in its own right.

At the South Asian end, the Siwalik Hills of Pakistan and northern India preserve large numbers of ape teeth and jaws in strata dating from about 12.7 to 8.5 million years ago. There are several important facial fossils too, the most famous of which preserves almost the entire face. The most abundant ape there was Sivapithecus. It persisted for more than four million years, across several stratigraphic units and many sites.

At the European end, one of the most revealing places lies northwest of Barcelona. It is a landfill called Can Mata. Building a landfill means opening up large areas of rock and sediment. Here, the digging exposed a whole succession of fossil sites.

The sites lie one above another, their ages resolved so finely that we can follow changes within the same basin over intervals of a few hundred thousand years. For paleontologists, this is a luxury. In most places, the events of several hundred thousand years are squeezed into a single layer.

One site produced an ape about twelve million years old, represented by more than eighty bones from the same individual: face, wrist, hand, pelvis, vertebrae, ribs. A fossil preserving the face, trunk, and hand together is an exceptional find among Miocene apes.

Several other apes appeared at different times in the same basin. One, dating to about 11.9 million years ago, had a very short face and thick enamel. Around ten million years ago, there was another. Europe's abundance of apes did not come from one extraordinarily long-lived genus. It came from one genus after another taking its turn.

To read an ape's movements from its bones, we look at a few key joints. Whether the shoulder blades sit on the back or on the sides of the body determines whether the arms can reach overhead.

The arrangement of the wrist on the little-finger side determines how far the wrist can turn. Curvature in the finger bones tells us whether the hand can remain hooked around a branch for long periods. The number of lumbar vertebrae tells us whether the trunk works more like a spring or a column.

Back to the ape from Can Mata. Its name is Pierolapithecus, and its bones have something rather unexpected to say.

Start with the trunk. The rib cage was broad and shallow rather than narrow and deep. The shoulder blades had moved onto the back instead of sitting on the sides, allowing the arms to rise overhead. The collarbones were relatively long. The joint on the little-finger side of the wrist had changed too, giving it greater freedom to turn. The lower back had become short and stiff. This was an animal capable of climbing upward with its body upright.

Now look at the hands. The fingers were relatively short and only slightly curved. These were not hands for suspending the whole body beneath a branch and swinging onward, grip after grip.

The body was upright; the hands were not built for hanging. We tend to picture an ape's body as a complete set: an upright trunk, long curved fingers, shoulders and wrists with a wide range of movement. The set looks as if it arrived in a single package. Pierolapithecus unpacks it. These features could appear separately, in different orders, and in more than one combination.

An upright trunk may have evolved more than once in ape history. A phylogenetic tree is a family tree of relationships; many reconstructions place upright Miocene apes on separate branches, suggesting repeated evolution. The number of origins still depends on fossil placement and reconstructed ancestral states. It is not inevitably two or more under every possible tree.

Arrangements that scatter these apes more widely suggest three or four. Section 5 will introduce a more extreme case: an animal that was not an ape at all independently evolved ape-like elbows and wrists.

Different lineages arrived at the same solution for themselves. Upright trunks and hands for hanging did not arrive together, and they did not arrive only once.

4 Two Apes in the Same Forest

About 11.6 million years ago, at least two kinds of ape lived in a forest at a place in southern Germany called Hammerschmiede. Today Hammerschmiede is a clay pit. As at Can Mata, the apes turned up where people were digging.

The larger ape was Danuvius. Several individuals have been found, preserving bones of the elbow, wrist, hand, hip, knee, foot, and spine. Estimated body weights range from the teens to more than thirty kilograms. The smaller ape, Buronius, was not named until 2024. It is known from just a few teeth and a bone from the knee. At an estimated ten kilograms, it weighed about as much as a small dog.

The most striking difference lies in their teeth. Danuvius had enamel about twice as thick as that of Buronius.

Enamel thickness tells us how much wear a tooth can withstand. Thick enamel equips a tooth to handle hard things, endure prolonged grinding, and stand up to grit mixed into the food.

Thin enamel often accompanies sharp cusps that can slice leaves, or a diet of softer food. It is not a menu. It tells us what the tooth was equipped to endure.

So these two apes probably ate different things, despite living in the same forest at the same time. A forest that could support apes with teeth so different must have offered distinguishable kinds of food.

Consider it the other way around. Had we found only one of them, we might have assumed that the forest's apes had just one way of feeding. A few additional teeth with thin enamel change our picture of the whole forest.

Tooth shape can tell us more. Leaves are difficult food: high in fiber, low in nutrients, and easier to digest when finely cut. Tall shearing crests joined into a line work like a row of little knives, well suited to slicing tough leaves.

Low, rounded cusps and broad, hollowed chewing surfaces suit fruit. Large back teeth with thick enamel suit crushing hard shells. A tooth's shape gives us a rough idea of what its owner was equipped to eat over a lifetime.

Its surface also carries minute scratches, visible only under a microscope. These record what an ape actually chewed in the last few days or weeks of its life. Hard seeds and nuts tend to leave small pits; tough leaves tend to leave long, fine scratches.

The interesting thing is that the two stories need not agree. Tooth shape tells us what an ape was equipped to eat; the scratches tell us what it actually ate in its last few weeks. Microwear on European Miocene ape teeth reveals every sort of diet: mainly soft fruit, mainly leaves, mainly seeds and hard objects.

The chemistry of the enamel can also distinguish between two broad groups of plants: trees and most herbaceous plants on one side, and the more heat- and drought-tolerant grasses that later spread across tropical open country on the other. Almost all the Miocene apes tested ate from the first group.

Not far to the west, during the same broad interval, another way of living appears. Can Llobateres and Can Feu in Spain have yielded skulls and partial skeletons of an ape from about ten million years ago called Hispanopithecus. The individual from Can Feu was an adult female weighing about twenty-two to twenty-five kilograms.

Its fingers were long and curved, its grip powerful. Shoulders, elbows, and wrists had a wide range of movement, and its trunk was upright. Hanging beneath branches offers one often-mentioned advantage: even a fairly heavy animal can reach the thin outermost branches and the fruit growing at their tips. It may be unable to balance on top of those twigs, but hanging below them allows its weight to be spread across several at once.

A 2012 study of its partial skeleton placed it among the earliest apes then known to have indisputable adaptations for hanging. Yet its hands also retained features for palm-down walking along the tops of branches. Even this ape could do both.

To the east, Rudabánya in northern Hungary has yielded several ape skulls from the same interval, as well as bones of the trunk, pelvis, and limbs. This ape was closely related to the Spanish one, so closely that they were once placed in the same genus. More recent analyses have increasingly separated them again.

Farther east, in Macedonia in northern Greece, lived a large ape with exceptionally thick enamel and a robust jaw, estimated to weigh several tens of kilograms. These features have been interpreted as adaptations to harder foods and a more seasonal diet. Some researchers think it spent more time on the ground, a judgment based chiefly on its teeth, body size, and the environment in which it was found.

Even a single ankle bone can speak. In 2025, a talus from Can Mata was redescribed. It indicated a way of moving in trees that fits none of today's apes. At the height of their diversity, Europe's apes had no ready-made living counterparts, not just for their hands and trunks, but even for their ankles.

Set these apes side by side at their peak and the spread is wide. Body weights ranged from about ten kilograms to several tens, with the largest perhaps reaching seventy or eighty kilograms.

They ate soft fruit, leaves, seeds, and hard objects. Some walked on all fours above branches; others traveled hanging beneath them; some did both. A few may also have spent substantial time on the ground. These were not a few variations on one kind of ape. They were several distinct ways of life, existing at the same time.

5 How Much of the Count Is Made by Taxonomy?

Begin with the oldest name. The first Miocene ape to be named was Dryopithecus, discovered in 1856 at Saint-Gaudens in southern France. Over more than a century, the genus came to accommodate material from many places, then gradually contracted again. Its boundaries have expanded and shrunk several times.

Today it refers only to a small European group. Its teeth, however, left a name in the textbooks. The five-cusped lower molar with a Y-shaped groove described in Section 1 is known as the “dryopithecine pattern.”

Now for a name that disappeared.

A genus called Ramapithecus once took up a great deal of space in textbooks. Established from jaws and teeth, it was long treated as a genus of its own and remained in the books for nearly half a century.

Then more complete facial fossils of Sivapithecus turned up in the Siwalik Hills. In 1982, a systematic comparison concluded that the two fell within the range of variation of a single genus. Under the rules giving priority to the earlier name, Ramapithecus was absorbed into Sivapithecus.

A substantial part of the difference between the two sets of forms was probably a difference between males and females. A genus disappeared, without a single bone going missing.

Some rearrangements go further. In 2015, Pliobates was interpreted as an early ape, partly because of its elbows and wrists. A 2024 craniodental analysis supported a pliopithecoid placement; the authors favored a stem-catarrhine interpretation, with ape-like joints evolving convergently. Including postcranial characters changed the tree, however. This was an argued interpretation, not unanimous agreement among all the anatomical evidence.

Its Chinese name still includes “ape,” while its taxonomic position may move wholesale. That is more drastic than merging two genera and makes it a serious candidate for the independent recurrence discussed in Section 3. The issue is not merely a new label: which similarities reveal ancestry and which convergence must still be assessed across different parts of the skeleton.

The opposite happens too. A group of Turkish fossils about 8.7 million years old had been assigned to the same genus as the large Greek ape. In 2023, new craniofacial material prompted researchers to separate them into a new genus, Anadoluvius. This was not the discovery of an animal that had never existed before. New material had shifted the boundary between genera.

Sometimes it is species, rather than genera, that are revised. Male and female apes can differ greatly; a male's canine teeth may be much larger than a female's. Ekembo from Rusinga had been divided into two species, one small and one large.

In 2025, researchers reassigned a large number of specimens and found extensive overlap in the body sizes of the two species. Much of the old “small one, large one” division had mistaken the difference between male and female canines for a difference between species. Both species were retained, but many specimens changed sides.

All these stories arise from the same predicament. Roughly half or more of the genera of Miocene apes were established chiefly from teeth, jaws, and fragments of faces. Roughly nine to twelve genera have reasonably substantial skulls or large portions of faces. Only six to eight have associated partial skeletons sufficient to discuss both trunk and limbs.

Teeth loom so large because enamel is the hardest tissue in a vertebrate's body. Bones rot, break, and wash away. Teeth often remain. Our first acquaintance with Miocene apes, then, is through their teeth.

Teeth can certainly distinguish genera and species. Cusp number, crown proportions, enamel thickness, and root shape all carry information. Yet within a single species, males and females, young and old, can have markedly different teeth too.

Lufeng in Yunnan has yielded thousands of ape teeth, which ought to be a large enough sample. Yet for decades researchers have kept revising how many species the teeth represent, or whether they are males and females of a single species. Simulations have specifically tested the practice of counting species from the spread of tooth sizes. The conclusion: that method alone cannot settle it.

Even many body-weight estimates are calculated from tooth size. More recently, researchers have turned to the inner ear. The shapes of the canals deep inside it offer another body of evidence, independent of teeth and bones, and have already been used to distinguish closely related genera.

The 2023 list is not frozen. Additions include Germany's Buronius, Turkey's Anadoluvius, and Masripithecus, reported in 2026 from roughly eighteen-million-year-old Egyptian deposits. Pliobates' position remains under discussion. With particular taxonomic choices one might count roughly thirty-six or thirty-seven genera and fifty-seven or fifty-eight species. That is illustrative bookkeeping, not an officially updated global census.

We can now answer the obvious question: how much more diverse were Miocene apes than apes today?

Living gibbons comprise about four genera and twenty-odd species. Orangutans have one genus and three species; gorillas, one genus and two species; chimpanzees, one genus and two species. That makes seven genera and about twenty-seven species altogether. Compare thirty-five to thirty-seven genera with seven, and the result is more than five times as many. Compare fifty-six to fifty-eight species with about twenty-seven, and it is only a little over twice as many.

Part of the reason those ratios differ so much is that today's gibbons are divided into twenty-odd species, raising the living species count. The more important issue, though, lies in the numerator and denominator themselves. The Miocene number includes every ape that appeared over nearly eighteen million years. The modern number includes those alive at this moment.

It is like comparing a school's roll of everyone who graduated over eighteen years with its list of pupils enrolled this year. Of course the graduate roll is longer. But those people never all sat in the same classroom at once.

What we can firmly say is this: taken cumulatively, Miocene apes diversified at the genus level far beyond what we see today. That conclusion is solid. How much more diverse were the apes living at any one moment? The margin was much smaller and far less certain. The fossils and the precision of their dates do not support claims of “five times” or “ten times.”

From here on, genus and species counts in this essay are cumulative. To say that Miocene apes were “five times as diverse as today's” is to compare the whole of nearly eighteen million years with today's roll call.

Using that convention, we can divide the Miocene into early, middle, and late intervals and count each separately: roughly ten to thirteen genera in the early Miocene, fifteen to eighteen in the middle, and eighteen to twenty-two in the late. A genus that crosses two intervals is counted in both, so these numbers show a pattern but should not be added together. The pattern rises throughout and peaks in the late Miocene. Yet the late Miocene is also when the pruning begins.

6 The Pruning

Between about 14.7 and 13.8 million years ago, Earth underwent a major episode of global cooling. Deep-sea sediments preserve its record: the Antarctic ice sheet expanded considerably, and ocean currents were reorganized along with it.

The warmest part of the Miocene was over. The climate did not cool in a straight line from then on. It oscillated with the cycles of Earth's orbit, but around a colder baseline.

The most direct explanation runs like this: temperatures fell, forests shrank, and the apes that depended on forests declined. Every link in that chain has evidence behind it. Most of these apes lived in trees. Their movements, hands, and trunks were built for branches. They could not do without forests.

And when apes later disappeared, they were often not alone. Many other European forest animals declined during the same interval. Farther on in the story, the spread of grasslands in South Asia also roughly coincides with the departure of its apes. This account fits the dietary evidence, the other animals, and the later vegetation. It is not an idle guess.

The difficulty is the timing. After the great global cooling, Europe's apes flourished for another four or five million years. Western and central European apes were most diverse between about 12.5 and ten million years ago: after the cooling, not before it.

So the version in which “the world cooled and the apes disappeared” does not fit the dates. Cooling was the backdrop, not the switch.

Imagine an old shop that stayed open for years after a great drought, then finally closed in a particular year. The drought surely had something to do with it. But what actually happened in the year the doors shut is a separate question.

The continents themselves were changing too. The Tibetan Plateau was rising, and the Asian monsoon was strengthening. An inland sea stretching from central Europe to the Caspian was retreating; the eastern Mediterranean was changing as well, altering moisture supply and land routes across Europe and western Asia. The East African rift was rising, casting rain shadows on either side. Each change affected the climate of its own region, on its own schedule.

The actual pruning came much later. Around 9.75 million years ago, mammal diversity in western Europe dropped sharply within a short interval, extinction rates rose, and the fauna as a whole was reorganized. Vertebrate paleontologists call this the Vallesian Crisis. “Vallesian” takes its name from the basin near Barcelona.

Most European apes disappeared around this reorganization. The forest fauna that included Hispanopithecus changed markedly at about this time. By roughly 9.5 million years ago, apes had all but vanished from the core areas of western Europe.

We can date the western European changes so closely because the strata there have such precise chronologies. As sediments are laid down, they record the direction of Earth's magnetic field. That field has reversed north and south many times, and each reversal provides a time marker that can be matched around the globe.

The layers in the basin near Barcelona have been correlated in just this way. That is why we can confine this round of ape disappearances in western Europe to the roughly quarter-million-year window between 9.75 and 9.5 million years ago.

Here is an unexpected detail.

Different rodents and shrews prefer different levels of moisture, so the small mammals found in a layer give us a rough indication of how wet the environment was. Researchers used the small mammals from the basin near Barcelona to reconstruct annual rainfall during this interval. They found no sudden drop in rainfall around the Vallesian Crisis to match the abrupt change in the fauna.

The cast of animals changed, but the amount of rain falling each year did not suddenly collapse. What, then, had changed?

“Forest contraction” tends to conjure a large patch of green being erased from a map. But several other changes are more common in practice, and more amenable to testing. Continuous stretches of interlocking canopy diminish. Forest breaks into patches with open ground between them. The difference between the wet and dry seasons grows.

In late Miocene Europe, these changes included a widening gap between the seasons. For different apes, each of these shifts would have carried a very different weight.

For an ape dependent on ripe, soft fruit and continuous canopy, sharper seasonality is the greatest danger. Fruit comes in seasons. In a forest without pronounced seasons, some kinds of tree are always fruiting, whatever the month.

Once the seasons become distinct, many trees crowd their fruiting into the same part of the year, leaving lean months between crops. Total annual rainfall can remain unchanged. But move the rain into different months, and the fruiting months move too. The hungriest stretch of the year grows longer and harder to endure.

An ape does not live by annual averages. It lives one month at a time. For an ape that lives on soft fruit, what matters is not the annual average but the hardest month of the year.

That offers one possible explanation for why the apes left even though annual rainfall did not change. For now, the explanation comes from aligning the diets indicated by teeth with the timing of environmental change. It has not been measured directly in that basin.

Following this line of thought, an ape with thick enamel and a powerful bite, capable of getting through the fruit-poor season on hard foods, might be less sensitive to such changes. The large, thick-enameled apes of Greece and Turkey did in fact linger nearly a million years longer than those of western Europe. This is a fit found after the event, not a prediction made beforehand. And they, too, eventually disappeared.

Keep one more thing in mind. Europe was the first region to be pruned, and it also has the densest record. We will return to that combination in the final section.

7 The Lights Go Out, Region by Region

When western Europe's apes had largely disappeared by about 9.5 million years ago, the pruning elsewhere did not happen in step. Put the last reliable records from each region in chronological order, and the sequence looks like this.

In central Europe, the record at Rudabánya in northern Hungary extends to about 9.5 million years ago, much like the western European record. In the Balkans and Anatolia, the large, thick-enameled Greek ape persisted until around 8.7 million years ago; Turkey's Anadoluvius dates to about 8.7 million years ago too. In South Asia, the last Siwalik record of Sivapithecus is about 8.5 million years old.

In Southeast Asia, the ape record from Thailand and Myanmar extends to roughly seven million years ago. These apes left only teeth and jaws, but the finds extend the known range of Miocene apes as far as Khorat in northeastern Thailand. In East Asia, Lufeng and Yuanmou in Yunnan carry the reliable record down to about seven million to a little over six million years ago.

The pruning was not a single cut. From western Europe to Yunnan, it unfolded over three or four million years, broadly from west to east, as the lights went out one region at a time.

The timing in each region roughly followed its own environmental changes. Western Europe went through the Vallesian Crisis. South Asia saw a strengthening monsoon, shifting river courses, and the beginnings of grassland expansion.

The forests of southwestern China remained wet and held out longest. The continental changes described in the previous section each reshaped a different region, so each region had its own timetable.

Africa has a different problem: sparse Late Miocene nonhuman-ape records. These examples are not endpoints for all apes, including later hominins: Nakali in Kenya, about 9.9 million years ago: one lower jaw and a dozen or so teeth. Samburu in Kenya, about 9.6 million years ago: one upper jaw with a few teeth. Chorora in Ethiopia, about eight million years ago: almost nothing but teeth.

Put all three sites together and they still cannot supply one complete ape. After them comes a long interval with almost no ape fossils at all.

There is one exception to this sequence, one that follows no continental timetable.

The area from Tuscany to Sardinia in present-day Italy was then a chain of islands separated by the sea. An ape called Oreopithecus lived there. Its most famous skeleton is almost complete, recovered from a lignite mine at Baccinello in Tuscany. Along with numerous other well-preserved skulls and bones, it makes Oreopithecus one of the best-preserved apes of the entire Miocene.

It had a relatively small brain and unusual teeth. Its hands, feet, and trunk all differed from those of mainland apes. Long shearing crests on the teeth indicate that it ate plenty of leaves. Island life was different from life on the mainland: little space, sea on every side, few animals coming and going.

An ape lineage confined to such a place for millions of years could readily develop a body unlike anything on the mainland. Oreopithecus did just that. It followed a path the mainland apes did not take, becoming so specialized that researchers have placed it in several radically different positions on the family tree.

The island apes outlasted many mainland western European lineages. Oreopithecus is recorded from about 8.3 to 6.7 million years ago, persisting nearly two million years beyond some earlier regional losses. This does not mean all mainland Eurasian apes had vanished, nor that every European region lost its last ape simultaneously.

At the far eastern end was Yunnan. The Lufeng Basin has yielded thousands of ape teeth and several skulls belonging to Lufengpithecus, one of the Miocene apes with the richest fossil collections.

A new analysis in 2025 showed that its diet was quite flexible, rather than tied to one kind of food. Nearby Yuanmou also yielded smaller apes, known mainly from teeth and jaws.

Southwestern China still retained a wet environment with extensive woodland. About three million years after western Europe's apes disappeared, there were still apes in the forests of Yunnan.

South Asia's story is bound up with grass. Chemical records preserved in ancient soils in northern Pakistan show a rapid spread of more heat- and drought-tolerant grasses between about eight and seven million years ago.

The last record of Sivapithecus, about 8.5 million years ago, slightly predates that rapid spread. But the monsoon was already strengthening, rivers were changing course, and grasslands had begun to expand little by little. More than “drying” lay behind the grasses' advance. Atmospheric carbon dioxide, the distribution of rain between wet and dry seasons, wildfire, and grazing animals were all changing the balance between trees and grass.

There is something else we need to set beside the apes' departure.

While apes were being pruned region by region, monkeys were branching out. In the early and middle Miocene, securely identified monkeys were far less diverse than apes. They consisted mainly of one early group found from North Africa to East Africa. In the late Miocene, however, the two great groups familiar today appeared in turn and then expanded: the largely leaf-eating colobines and the broadly omnivorous macaque group.

The two transverse ridges on a monkey's molars work like two rows of blades, excellent for cutting leaves. It was during this interval that the contrast introduced in Section 1 reversed: a Miocene with many apes and few monkeys gave way to a present with many monkeys and few apes.

Under the same broad conditions, monkeys were not pruned in step with apes. They grew new branches instead. This was not simply a case of a worsening environment reducing all tree-dwelling primates together.

Did the monkeys push the apes out? Their molars, faster reproduction, and adaptations to leaves and somewhat more open habitats may all have given them an advantage as the seasons became more distinct. Yet monkeys and apes coexisted for long periods in many places, and regional ape disappearances do not align exactly with monkey expansion. Competition remains a candidate explanation, not a demonstrated main cause.

8 The Remainder Lies Where the Two Prunings Fail to Align

First, let us take stock of what was pruned away.

Not just thirty-odd names. A whole set of bodies with no living counterparts: Nacholapithecus, with its long lower back and capable grasping hands; Pierolapithecus, with its upright trunk and hands unsuited to hanging; two apes in the same forest whose enamel differed twofold in thickness; the small-brained, leaf-eating island ape.

Hand proportions provide a clear example. Several Miocene apes had moderately long fingers and relatively long thumbs, a combination no longer found among living apes. Miocene ape hands were not scaled-down versions of a few living ape hands.

Then comes a straightforward question. Was there any difference between those pruned away and those that held on longer?

No single shared ability has been demonstrated to explain all the survivors.

Ekembo left so many specimens on Rusinga that they can still be reassigned one by one, yet it disappeared early. Sivapithecus persisted in South Asia for more than four million years, over a wide range, yet did not survive past 8.5 million years ago. Thick-enameled apes disappeared, and thin-enameled apes did too. The most highly specialized island lineage, meanwhile, lasted remarkably late. The flexible feeder Lufengpithecus lasted later still, but did not make it beyond the Miocene either.

Researchers have studied diets, and they have studied changes in forests. But no analysis has yet brought together the body sizes, diets, ranges, and habitats of all Miocene apes to predict which would survive to the end of the epoch. No single trait has been shown, on its own, to predict which apes would last longer. That sentence blocks a very tempting reading: if some lasted and others vanished early, surely the survivors must have had something special. Among the Miocene apes, we have yet to find that “something.”

Now we come to this essay's addition to the catalogue of remainders. The apes in this story were deleted twice.

The first deletion was real: extinction. It advanced region by region, earliest in western Europe, around 9.5 million years ago, latest in East Asia, around six million years ago. The island lineage followed its own path. That ordering is limited to the regions and fossil lineages compared here, not a route map of all apes disappearing from Eurasia.

The second deletion happened in the record. It followed a different set of rules: where sediments were suitable, where people dug, where layers could be resolved into intervals of tens of thousands of years.

Western Europe has one of the densest records in the world, with an exceptionally fine sequence of layers in the basin near Barcelona. Late Miocene Africa is another story. An earlier review counted only about seven securely identified ape-bearing sites on the entire continent between roughly eleven and five million years ago. And more than half the genera have left only teeth and jaws.

The two deletions do not line up. Our clearest view of the lights going out comes from the very place where apes disappeared first.

Western Europe, with the densest record, was the first region to lose its apes. Those six million years in Africa are almost completely dark. The record can tell us next to nothing about what apes there were like in the late Miocene. The tool from Episode 18 applies here too: the sparser the record, the farther the last fossil may lie from the actual day of disappearance. Seven sites in six million years is so sparse as to be almost unusable.

Imagine a graph. Time runs along the horizontal axis, with one line for each region. The length of a line shows how long apes really lived there. Its thickness shows the density of the record.

Western Europe's line is not long, but it is the thickest. Africa's starts earliest, then becomes so thin in its latter half that it almost vanishes. Yunnan's ends latest.

Superimpose the two deletions and the resulting curve can look steeper than the real decline. Ape numbers fall in a region with a dense record, while regions with sparse records cannot fill out the global tally. Add up the genera from each region, and the line plunges.

It is not all an illusion. Western Europe's own dense, continuous record documents the loss of multiple genera between about 9.75 and 9.5 million years ago. That part is firm. The scale of the global decline is much less secure, and the African gap is the weakest part of all.

The second deletion cuts elsewhere too. More than half the genera are reduced to teeth, so what we know best about most of the apes pruned away is how they chewed. How they moved, how they held a branch, how large their brains were: for only six to eight genera can we say even a little.

More thoroughly lost are the apes that never entered any fossil site at all. Seven African sites in six million years: the apes that were never once buried in the right place will appear on no list. Taxonomy did not remove them. They were never registered in the first place.

Episode 11 described the fossil record as a sieve, not an inventory. Here there are two sieves: extinction itself, and the record. Both remove things, but they do not remove the same things. What becomes visible is the portion that happens to make it through both.

So here is the fifteenth kind: the remainder lies where the two prunings fail to align.

It needs its own entry, separate from Episode 11's “remainder in the sieve.” There, we had one sieve, and the remainder was what it missed. Here we have two. The remainder lies in neither sieve alone, but where their holes fail to line up.

It must also be kept distinct from Episode 12. That essay had two sieves too, one of footprints, one of bones. But both were sieves of the record, and their misalignment scrambled the order of events. Here, one sieve is extinction itself. The thing being measured is doing some of the deleting. What the mismatch distorts is not the sequence, but the shape and scale of the decline.

This is another form of the two-layer construct explored in this series. Extinction is the first layer: evolution's own pruning. The record and its classification form the second: paleontology's pruning. Even the count of “thirty-odd genera” is subject to mergers, splits, and removals. Each layer deletes things and leaves a remainder of its own. The two remainders do not coincide.

What evolution deletes is whole bodies, whole ways of eating and moving. What paleontology deletes is individuals never buried in the right place, sites never excavated, and names merged out of existence. We can glimpse only a small part of the first list through the gaps in the second.

This kind of remainder has a very practical use. The next time we see a curve labeled “Miocene ape diversity through time,” we can begin by asking how much of its shape was traced by the apes themselves, and how much was determined by the holes in the two sieves.

Finally, following this series' usual practice, we should ask whether there was a change of level. Episode 10 set a criterion: the unit responsible for reproduction must move to a different level, as when a group of cells becomes a single multicellular individual that reproduces as a whole. There was no change of level here. From beginning to end, the reproductive units were individual apes. Both radiation and pruning happened within the same level.

Return, at last, to the map we began with. Ten million years ago, the forests from Spain to Yunnan held many kinds of ape. Most left only teeth. A few left entire skeletons. Some, perhaps, did not leave even a tooth. One sieve removed them; another lets us see them. The holes in the two sieves are not in the same places.

Next, we turn from the surviving branches to the lines we ourselves drew while telling their history.