Paleoenvironments

Paleoenvironment means ancient environment, so paleoecologists study environments in the distant past. Researchers study the environments of our ancient ancestors to better understand the context of our evolution. They ask questions that help us understand the environmental factors and changes that might have impacted how we evolved.

When we think of environments, we tend to think of the plants and animals that live there like this young male lion in mixed thorn and marula woodlands. Paleoecologists use modern environments of both vegetation and animals to help reconstruct the paleoenvironments.

There is also another type of environment that paleoanthropologists study—geologists often use the term to describe the way the soil in which fossils are found was deposited, sometimes called depositional environments and includes sands, silts, clays, etc. This is important for understanding how the fossils that we find got into the soils in which they are found. In this picture you can see the different colored layers in the ancient soils that represent river and lake deposits from the Ledi-Geraru Research area in Ethiopia.

Paleoecologists reconstruct the paleoenvironment with both abiotic and biotic factors. Abiotic contributions include climate (temperature, rainfall, seasonality), volcanic activity, and types of soils. Biotic factors cover plants, vegetation structure, and animals. Modern animals and their communities are used as analogs to look at the past. We use our understanding of how modern animals lived and the environmental conditions in which they lived to better model the environmental conditions of fossil animals and how they lived. For example, animal communities that live in the forest (like the vervet monkey in the image on the left) will have many more species of animals that are arboreal (adapted for living in trees) and frugivorous (adapted for eating fruits) than those that live in grassland (like the Cape Buffalo in the image on the right).

We can look at the locomotor and dietary adaptations of the animals found at a fossil site to determine how many of them were arboreal versus terrestrial (adapted for living on the ground) and frugivorous versus grazers (adapted for eating grass) and compare them to animal communities from modern sites to better understand their community structure and what it tells us about the environment.

Seasonality in Africa is defined by wet and dry seasons—not by winter snow and fall leave colors like the northern hemisphere. The image of buffalos below shows the environmental contrast in the dry season.

Studies of the sediments, animals, and plants from early hominin sites show that many early hominin species lived in mosaic habitats, in other words, habitats with different vegetation types. They are often a mix of woodland, bushland, shrubland, grassland, and riverine forest.

However, over the course of our evolutionary history (spanning about 7.0 million years), the climate got cooler and drier globally, which had an impact on the local environments where hominins lived, resulting in the expansion of grasslands and increase in seasonality (in Africa this means an increase in the length of the dry season when there is no rain). This shift probably happened around the same time as the origin of Homo, the genus to which humans belong. An extremely seasonal and arid environment can be seen in this modern picture of Sommering’s gazelles in the Ledi-Geraru research region.