Early apes lived in a constantly changing world of fire and ash

Human evolution is not only about bones. It is about the forests, soils, and climates that supported early apes long before the first hominin walked upright.

Though great apes diverged from other primates around 25 million years ago, our own lineage did not appear until roughly 5 million years ago. In that immense stretch of time, forests rose and fell, volcanoes erupted, and ancient creatures adapted to the world around them.

One place where this deep story unfolds is western Kenya’s Koru 16. This fossil site captures a snapshot of life during the early Miocene, around 20 million years ago. Preserved by ash from the long extinct Tinderet Volcano, Koru 16 is a rich and complex time capsule.

New research led by Venanzio Munyaka reveals that the story of ape evolution cannot be told without understanding the ecosystems they called home. The study adds fresh insight to a region already steeped in fossil history.

Ape fossils reveal evolutionary activity

Koru 16 has drawn scientific interest for nearly a hundred years. The site’s first primate fossils were discovered in 1927, and legendary anthropologist Louis Leakey led several excavations in the decades that followed.

While those early efforts laid important groundwork, the last decade brought new urgency and better tools for understanding its full ecological context.

Between 2013 and 2023, Munyaka and colleagues carried out a detailed investigation at two subsites. They recovered nearly 1,000 fossil leaves and a wealth of vertebrate remains.

The bones came from 25 different species, including pythons, rodents, and three types of apes. These included Proconsul africanus, Proconsul major, and a newly identified large bodied nyanzapithecine.

These discoveries make Koru 16 the most ape rich site within the wider Tinderet group. The presence of multiple ape species in a single forested environment suggests the region played a key role in early ape evolution. But it was not just the bones that told a story.

Changing forests shaped how early apes lived

The team used a combination of paleosol chemistry, leaf structure, and tree stump fossils to reconstruct what Koru 16 looked like millions of years ago. Their results point to a warm, wet tropical forest, interrupted frequently by natural disturbances.

Volcanic eruptions from the Tinderet complex blanketed the land with ash. Wildfires and seasonal floods added further stress.

Yet through all this, life thrived. Soil analyses indicate the region received about 2,000 mm of rainfall per year, with temperatures likely above 25°C. These conditions are similar to modern tropical forests in Africa, though the vegetation was slightly different. Koru 16’s forest likely had more deciduous trees, with plants that dropped their leaves seasonally.

“By studying the soil, fossils, and tree stumps, we could recreate the forest’s climate,” said Munyaka. The climate was not stable. Instead, it was a shifting mosaic of dense forest, open patches, and recently disturbed areas. This landscape would challenge and shape the creatures living there.

Leaves, light, and forest layers

Plant fossils offered a vivid picture of this forest. From the two subsites, researchers cataloged 18 distinct leaf morphotypes. These belonged to plants that likely had short lifespans and fast growth cycles.

Such traits suggest a forest marked by high turnover, where plants quickly colonized open areas after fires or ashfalls.

Most of the fossilized leaves came from species adapted to both shaded understories and sunlit clearings. This indicates a mixed canopy, with parts of the forest densely shaded and others exposed. The forest structure would have influenced how apes moved, fed, and nested.

Some leaves had characteristics similar to those found in modern forests in Uganda and Madagascar, places where rainfall is seasonal and disturbance is common.

The researchers also found casts of fossilized tree stumps. In one subsite, stumps stood close together, suggesting a mature, shaded forest. In the other, stumps were widely spaced, hinting at a more open, disturbed area.

These contrasts imply that even within a small region, early Miocene forests were ecologically diverse and constantly in flux.

Apes among the ash

The fauna found alongside the plants reinforce this view. Apes were not alone. The site also yielded fossils of large pythons and several rodent species. The dominance of rodents reflects a rich, layered ecosystem.

Most importantly, the three ape species discovered show that such forests supported a range of primate forms, including some of our most ancient relatives.

“The forest was not a quiet, uniform place,” said one researcher. “It was full of challenges that spurred change.” These challenges likely encouraged the development of new behaviors. Apes may have moved more on the ground, adapted their diets to seasonal food, or evolved new social habits to cope with ecological instability.

This type of environment, warm, seasonal, and disturbed, would have offered opportunities and obstacles. Forest fragmentation and frequent change may have nudged primates toward flexibility in how they lived, moved, and survived. In that sense, the forest itself became an evolutionary partner.

Ecological roots of evolution

Koru 16 forces a shift in how we think about ape origins. Rather than emerging in calm, unchanging rainforests, early apes lived in dynamic, fractured landscapes.

These habitats were shaped by fire, flood, and ash. The soil, climate, and plants constantly shifted, creating a stage that demanded adaptability.

The presence of multiple ape species in this kind of forest suggests that environmental variability did not limit primate evolution. It may have energized it. The ability to navigate change, rather than thrive in stability, might have been a key evolutionary trait.

Through its ancient layers of ash and soil, Koru 16 gives us something rare. It offers a full picture of the world early apes inhabited. It tells a story not just of bones, but of climate, ecology, and survival.

The research reminds us that the journey to becoming human began not just in upright steps but in leafy canopies, open glades, and the fertile ash beds of a forest always on the move.

The study is published in the journal Paleoceanography and Paleoclimatology.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–