Understanding what the environment looked like millions of years ago is essential for piecing together how our earliest ancestors lived and survived. Habitat shapes everything, from what food was available, to where water could be found, to how predators and prey interacted.
For decades, scientists studying South Africa’s Cradle of Humankind have tried to reconstruct the landscape in which species like Australopithecus sediba, Paranthropus robustus and Homo naledi once lived. These were hominins that inhabited the region between roughly 2.5 million and 0.25 million years ago. The Cradle of Humankind is a Unesco world heritage site that has remained the single richest source of early human fossils for over 90 years.
A long-standing idea has been that the Cradle experienced a dramatic environmental change around 1.7 million years ago: a shift from woodlands to open grasslands. This shift likely happened as global climates became cooler and drier, with stronger seasonal patterns. These broader changes, linked to the expansion of polar ice sheets and shifts in atmospheric circulation, reduced the availability of year-round rainfall in southern Africa.
Trees and shrubs, which depend on consistent moisture, gave way to hardy grasses better suited to long dry seasons and intense sunlight. In the woodlands, dense trees and shrubs had once provided leafy vegetation for browsing animals. As the landscape opened up, short grasses became dominant, supporting grazing animals.
This supposed sudden transformation was thought to have reshaped the setting in which early humans evolved, possibly influencing their diets, mobility and survival strategies.
But was there really such a sudden switch?
I’m a palaeoecologist who’s part of a team that specialises in reconstructing ancient environments by studying fossil animals. We set out to test the “sudden switch” idea, using a large dataset of fossil antelope teeth. Antelopes (bovids) are particularly useful for reconstructing past environments in Africa: they are abundant in the fossil record, they occupy a wide range of habitats today as well as in the past, and their teeth preserve clear signals of what they ate.
We examined more than 600 fossil teeth from seven well-dated sites in the Cradle, covering a broad time span from 3.2 million to 1.3 million years ago.
The results of our study were striking. Across all seven sites, spanning nearly two million years, the antelopes show consistently strong grazing signals. Grass-eating was dominant throughout the period, challenging the old model of a sudden woodland-to-grassland shift 1.7 million years ago. Instead, the evidence points to a more stable but varied landscape: a mosaic environment. Some fossil species even showed different feeding strategies from their modern relatives, highlighting that ancient antelopes adapted to past conditions in distinct ways.
This tells us more about the world early humans evolved in – but it also reminds us to be cautious. Fossil animals didn’t always behave like their modern relatives, so drawing direct parallels risks oversimplifying the past.
Dating the sites
To interpret the fossils in context, we needed to be sure of when each site formed. Previous work often relied on broad age estimates based on the types of animals found in each sediment layer – a method called biochronology – which could only give a rough idea of when different species lived. This made it difficult to line up fossils from the many cave sites in the Cradle on a reliable timeline. Thanks to recent improvements in radiometric dating, a method that finds the precise age of rocks by measuring how radioactive elements change into other elements over time, the chronology of the Cradle has been refined.
The layers of calcite deposited in caves (known as flowstones) were recently shown by geochronologists to have formed at the same time across multiple sites, providing a regional framework for the whole area. This means researchers can now compare fossils from different caves knowing they represent the same windows of time. It’s a huge step forward in testing whether environmental shifts were truly regional events.
Reading diets from teeth
The method used in this study is called dental mesowear analysis. It records the long-term impact of diet on the tooth surfaces of herbivores throughout their life. In simple terms, different diets wear teeth in different ways:
- browsers (like kudu or giraffes), which eat leaves and twigs, usually have sharper cusps, because their food causes less wear on the teeth
- grazers (like wildebeest or zebra), which feed mostly on grasses rich in silica and often covered in grit, develop blunter cusps from heavy tooth grinding
- mixed feeders show intermediate wear, reflecting generalist behaviour and a diet that shifts with seasons or local vegetation.
By scoring cusp shape and relief on each fossil tooth, we assessed whether past populations leaned more towards browsing or grazing.
The results showed there was a mix of different habitats in this environment at that time: open grassy areas mixed with patches of trees and shrubs. This would have created a patchwork of ecological niches, offering early humans a diverse range of resources.
Some sites – including the famous Sterkfontein Caves, home to one of the most complete early hominin skulls ever found, “Mrs Ples” – showed a bimodal pattern in tooth wear, meaning that even within the same community, some antelopes were grazing while others were browsing. This suggests that vegetation structure shifted locally or seasonally, and that animals adapted their diets accordingly. They switched between food sources as conditions changed.
Read more:
Elephant teeth: how they evolved to cope with climate change-driven dietary shifts
Lessons from antelope diets
One of the most important findings is that some fossil antelopes fed very differently than their modern relatives. For example, certain groups that today are almost exclusively browsers were much more grass-focused in the Cradle fossil record. Others showed unexpected flexibility, with individuals of the same tribe in the same site adopting different strategies.
This has two key implications.
We cannot always rely on modern analogies. Assuming extinct animals behaved like their living relatives can be misleading, since the fossil record shows surprising shifts in diet. This means reconstructions based only on which species were present may give the wrong impression or oversimplify the reality.
Flexibility was crucial. The fact that antelopes could switch between grazing and browsing indicates that the Cradle’s environment was dynamic, and that survival often depended on adaptability. This echoes what we know about early humans, who also seem to have thrived by exploiting a wide range of resources.
Megan Malherbe is affiliated with the Institute of Evolutionary Medicine at the University of Zurich, and the Human Evolution Research Institute at the University of Cape Town.
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