Discovery sheds new light on the habitat of early apes

Baylor University researchers, in collaboration with an international team of scientists, have discovered definitive evidence of the environment inhabited by the early ape Proconsul on Rusinga Island, Kenya. The groundbreaking discovery provides additional information that will help scientists understand and interpret the connection between habitat preferences and the early diversification of the ape-human lineage

Their research findings -- published this month inNature Communications -- demonstrate that Proconsul and its primate relative Dendropithecus inhabited "a widespread, dense, multistoried, closed canopy" forest.

Daniel Peppe, Ph.D., assistant professor of geology in Baylor's College of Arts and Sciences, said that previous work on the fossil sites on Rusinga Island suggested a variety of contradictory environmental preferences for Proconsul and that none of the previous work could definitively tie Proconsul to a specific habitat.

"Our research findings provide direct evidence and confirm where the early ape lived about 18 to 20 million years ago," Peppe said. "We now know that Proconsul lived in a closed-canopy, tropical seasonal forest set in a warm and relatively wet local climate."

Lauren Michel, lead author of the study and a doctoral student in the geology department at Baylor, was among the team of international researchers who found fossils of a single individual of Proconsul among geological deposits that also contained tree stump casts, calcified roots and fossil leaves. This discovery "underscores the importance of forested environments in the evolution of early apes," Peppe said.

"While excavating one of the major fossil sites on Rusinga Island, our team found four teeth from Proconsul amid an expansive fossil forest system," Michel said. "Ultimately, we were able to find 29 tree stump casts and unearth root casts in the same horizon as the fossil teeth."

"The varying diameters of the tree stumps coupled with their density within the fossil soil, implies that the forest would have [comprised] trees with interlocking or overlapping branches, thus creating a canopy," Michel said. Also, further evidence from the excavation site has shown that the landscape was "stable for decades to a few hundred years while the forest grew," Michel added.

Adding to the novelty of the research teams' findings is how all of forest artifacts were contained in one layer or strata.

"What is spectacular about this discovery is that all of these individual elements--tree stumps, leaves, roots, animals--are tied together in a single stratigrap

hic interval. This gives us tremendous resolution in reconstructing the specific environment inhabited by one of our early ape ancestors," said Kieran P. McNulty, Ph.D., co-director of research on Rusinga Island and associate professor of anthropology at the University of Minnesota.

Researchers were also able to determine the climate for the fossil forest.

"Evidence from the forest fossil soil suggests that the precipitation was seasonal with a distinct wet and dry period. During the dry season, there was probably relatively little rainfall," Peppe said. "Additionally, by studying fossil leaves at the site, we were able to estimate that there was about 55 to 100 inches of rainfall a year and the average annual temperature was between 73 and 94 degrees Fahrenheit."

Research on Rusinga Island has been ongoing for more than 80 years and has resulted in the collection of thousands of mammal fossils, including many well-preserved specimens of Proconsul and other primates. Evidence from these fossils of Proconsul indicate that it probably had a body position somewhat "similar to modern monkeys," but that details of its anatomy suggest some "more ape-like climbing and clambering" abilities. Since 2011, the team's research at the fossil forest site has resulted in the collection of several additional new primate fossils.

"This understanding of Proconsul's skeletal anatomy and how it moved demonstrates that the species was well-suited for life in a dense, closed canopy forest, which is consistent with our findings," Michel said.

Other contributing authors to the study include: Steven G. Driese of Baylor University; William H. Horner of Baylor University and Colorado State University; James A. Lutz of Utah State University; Holly M. Dunsworth of University of Rhode Island; William E. H. Harcourt-Smith of Lehman College, City University of New York, and the Natural History Museum; Thomas Lehmann of Senckenberg Research Institute ; Sheila Nightingale of City University of New York and Kieran P. McNulty of University of Minnesota.

Habitat of early apes: Evidence of the environment inhabited by Proconsul

University of Rhode Island anthropologist, along with colleagues from an international team of scientists, has discovered definitive evidence of the environment inhabited by the early ape Proconsul on Rusinga Island, Kenya. The findings provide new insights into understanding and interpreting the connection between habitat preferences and the early diversification of the ape-human lineage

The early ape Proconsul (center) and the primate Dendropithecus (upper right) inhabited a warm and relatively wet, closed canopy tropical seasonal forest 18 million years ago in equatorial eastern Africa (Rusinga Island, Kenya).

Their research, which was published today in the journal Nature Communications, demonstrates thatProconsul and its primate relative Dendropithecusinhabited "a widespread, dense, multistoried, closed canopy" forest.

Holly Dunsworth, URI assistant professor of anthropology, said that the research team found fossils of a single individual of Proconsul, which lived 18 to 20 million years ago, among geological deposits that also contained tree stump casts, calcified roots and fossil leaves. The discovery underscores the importance of forested environments in the evolution of early apes.

"To have the vegetation of a habitat preserved right along with the fossil primates themselves isn't a regular occurrence in primate paleontology," she said. "It's especially rare to have so many exquisite plant fossils preserved at ancient ape sites."

Rusinga has been known since the 1980s for preserving a fossil ape and other creatures in a hollowed out, fossilized tree trunk. But it wasn't until the research team's discovery of additional tree trunks and fossil primates preserved in the same ancient soil that there was a strong link between the ape and its habitat at the site.

"It's probably the best evidence linking ape to habitat that we could ask for," Dunsworth said. "Combined with analyses of the roots, trunks and even beautifully preserved fossil leaves, it's possible to say that the forest was a closed canopy one, meaning the arboreal animals, like Proconsul, could easily move from tree-to-tree without coming to the ground. This environmental evidence jibes with our behavioral interpretations of Proconsul anatomy--as being adapted for a life of climbing in the trees--and with present-day monkey and ape ecology."

Additional evidence from the excavation site has shown that the landscape was stable for many years while the forest grew.

According to co-author Daniel Peppe of Baylor University, evidence from the forest soil suggests "the precipitation was seasonal with a distinct wet and dry period. During the dry season, there was probably relatively little rainfall," he said. "Additionally, by studying fossil leaves at the site, we were able to estimate that there was about 55 to 100 inches of rainfall a year and the average annual temperature was between 73 and 94 degrees Fahrenheit."

Research on Rusinga Island has been ongoing for more than 80 years and has resulted in the collection of thousands of mammal fossils, including many well-preserved specimens of Proconsul and other primates. Evidence from these fossils indicate that Proconsul probably had a body position somewhat similar to modern monkeys, but that details of its anatomy suggest some more ape-like climbing and clambering abilities. Since 2011, the research team's work at the fossil forest site has resulted in the collection of several additional new primate fossils.

Dunsworth said that her work at the site is continuing.

"We don't know exactly what we're going to find, but without a doubt, if we keep searching, we're going to find knowledge about early ape evolution, which was, of course, a significant chapter in our own history," she said.