February 20, 2014

Forested Environments Were Important In The Evolution Of Early Apes

April Flowers for - Your Universe Online

Definitive evidence of the environment where the early ape Proconsul lived on Rusinga Island, Kenya, has been discovered by an international team of scientists led by Baylor University. This discovery will provide new data to help researchers understand and interpret the connection between habitat preferences and the early diversification of the ape-human lineage.

The groundbreaking findings, published in Nature Communications, reveal that Proconsul and its primitive relative Dendropithecus lived in "a widespread, dense, multistoried, closed canopy" forest.

Prior research on the fossil sites located on Rusinga Island have suggested a variety of contradictory environmental preferences, said Daniel Peppe, assistant professor of geology in Baylor's College of Arts and Sciences. He noted that none of the previous studies could provide a definitive answer for the question of what specific habitat Proconsul inhabited.

"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."

The team found fossils of a single individual of Proconsul among geological deposits containing tree stump casts, calcified roots, and fossil leaves. Peppe said that this discovery "underscores the importance of forested environments in the evolution of early apes."

"While excavating one of the major fossil sites on Rusinga Island, our team found four teeth from Proconsul amid an expansive fossil forest system," Lauren Michel, doctoral student in the Baylor geology department, 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 been comprised of trees with interlocking or overlapping branches, thus creating a canopy," Michel told Baylor's Tonya B. Lewis. Additional evidence from the excavation site revealed that the landscape was "stable for decades to a few hundred years while the forest grew," Michel added.

Another unique aspect to the findings is how all of the 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 stratigraphic 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.

Determining the climate for the fossil forest was also made possible by the single interval.

"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."

Rusinga Island has been a sight for ongoing research for over 80 years, resulting in the collection of thousands of mammal fossils—including many well-preserved specimens of Proconsul and other primates. The Proconsul fossils have provided evidence indicating that it probably had a body position somewhat "similar to modern monkeys." The details of its anatomy, however, suggest "more ape-like climbing and clambering" abilities. The research team has worked at the forest fossil site since 2011, collecting 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.