Anthropologists have long believed that apes evolved to stand upright to gather fruit in forests, but new research from the University of Michigan suggests that they developed their upright stature to grasp leaves.

The research focused on a 21-million-year-old fossil ape called ‘Morotopithecus’, and scientists found that the early apes of that era ate leaves and lived in a seasonal forest with open grasslands rather than dense canopy forests as previously believed. until today.

The research emerged from a collaboration of paleontologists internationally, known as the Research on East African Catarinas and the Evolution of Hominids (REACHE), where each of the scientists focuses on different aspects of the paleoenvironment of the early apes.

This particular study, led by paleoanthropologist and professor in the Department of Anthropology at the University of Michigan, Laura McLatchie, focuses on a 21-million-year-old site called the Moroto site in eastern Uganda. There, the researchers examined fossils found in a single stratigraphic level, including fossils of the oldest clearly documented ape, Morotopithecus. In the same layer were fossils of other mammals, ancient soils called paleosols, and tiny particles of silica from plants called phytoliths. Through these findings the researchers recreated the ancient environment of Morotopithecus. As they discovered, the plants that grew in this landscape experienced seasonal periods of rain and drought. This also means that at least part of the year the apes had to rely on something other than fruit to survive. As indicated by the findings, Morotopithecus lived in an open forest consisting of trees and shrubs.


The first indication that these ancient apes ate leaves was in their molars, which were very “pointed” like the molars used to tear fibrous leaves. In contrast, molars used for eating fruit are usually more rounded, according to Ms McLatchie. The researchers also examined the tooth enamel of monkeys as well as other mammals found at the same stratigraphic level. From the isotopic ratios in the tooth enamel they inferred that the apes and other mammals ate water-stressed plants that are more common in open forest or grassy forest environments.

“Now that we have shown that such environments existed at least ten million years before the evolution of bipedalism, we must also rethink human origins,” notes Ms. McLatchie.

The research, published in the journal Science, therefore not only sheds light on the origin of monkeys, but also overturns our knowledge of the origin of woodlands. Researchers previously believed that Equatorial Africa during the early Miocene was densely forested and that open woodlands and grassy areas appeared only 7-10 million years ago. On the contrary, with the present research this development is placed at 21 million years ago.

A second companion study uses a set of environmental data to reconstruct the vegetation structure at nine ape fossil sites across eastern Equatorial Africa during the early Miocene, including the Moroto site. It turns out that grass was everywhere during that time period, says John Kingston, a biological anthropologist and associate professor in the Department of Anthropology at the University of Michigan.