An artist's rendering of a woodland habitat with an ape climbing...

An artist's rendering of a woodland habitat with an ape climbing a tree in Uganda, with the Mount Moroto volcano in the background. A fossil relative of an elephant forages at center, back. Credit: Stony Brook University / Corbin Rainbolt

Prehistoric apes evolved millions of years earlier than originally believed, learning to stand upright to reach edible leaves in grassy woodlands, according to two new research papers from an international team of paleontologists, including a Stony Brook University professor.

The research, more than a decade in the making, pushes back the time frame when apes became larger and upright in equatorial Africa to 21 million years ago. The findings potentially force scientists to rethink the species' evolution and how human bipedalism developed millions of years later.

Researchers had previously believed the change to apes being upright occurred some 7 million to 10 million years ago.

James Rossie, an associate professor in Stony Brook's Department of Anthropology and a member of the international collaboration, said a changing environment encouraged apes to transition to consuming leaves when fruit was less abundant.

"Eating more leaves encouraged increased body size to help digest them," said Rossie, who spends about half of his summers in Africa working on the research, funded by National Science Foundation grants. "That size increase required a solution to weight-bearing in the small branches of trees. The result was more flexible upright climbing adaptations that allow the ape to spread its weight among multiple tree branches."

Rossie says that the group’s main mission was “understanding ape origins, which of course has laid the foundation for human origins.”

The two papers, published this week in Science, are the product of a group of international paleontologists known as the Research on Eastern African Catarrhine and Hominoid Evolution project, or REACHE. 

The first paper revolves around a 21-million-year-old ape fossil named Morotopithecus from Moroto, a town in the northern region of Uganda. 

Rossie assisted in the dental analysis of a newly discovered lower jaw fragment fossil of Morotopithecus, which the group used to recreate the environment of Moroto. The team determined that Morotopithecus' elongated molars were ideal for slicing leaves and were unlike the low, round, crushing tooth cusps of "committed" fruit eaters. 

A companion paper detailed how scientists reconstructed the environment of that historical period in several eastern African locations using the carbon isotope analysis of ancient soil organic matter. The authors found that tropical grass habitats in Africa were abundant at least 10 million years earlier than originally believed, calling for revised interpretations of mammalian evolution.

Robin Bernstein, program director for biological anthropology at the National Science Foundation, said the research creates a new framework for future studies of ape evolution.

“The findings have transformed what we thought we knew about early apes, and the origin for where, when and why they navigate through the trees and on the ground in multiple different ways,” Bernstein said in a statement. “For the first time, by combining diverse lines of evidence, this collaborative research team tied specific aspects of early ape anatomy to nuanced environmental changes in their habitat in Eastern Africa, now revealed as more open and less forested than previously thought."

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