Paleontologists and anthropologists led by Dr Kieran McNulty from the University of Minnesota have discovered definitive evidence of the widespread, dense, multistoried, closed-canopy tropical seasonal forest with a warm and relatively wet, local climate inhabited by the early Miocene ape Proconsul, and its relative primate Dendropithecus, on Rusinga Island, Kenya.
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 – on Rusinga Island, Kenya. Image credit: Jason Brougham.
“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,” said Dr Daniel Peppe of Baylor University, who is a co-author of the paper published in the journal Nature Communications.
“Our research findings provide direct evidence and confirm where the early ape lived about 18 to 20 million years ago.”
“We now know that Proconsul lived in a closed-canopy, tropical seasonal forest set in a warm and relatively wet local climate.”
Dr McNulty, Dr Peppe and their colleagues 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,” Dr Peppe noted.
“While excavating one of the major fossil sites on Rusinga Island, our team found four teeth from Proconsul amid an expansive fossil forest system,” added Lauren Michel, a doctoral student at Baylor University.
“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.”
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. Adding to the novelty of the 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 stratigraphic interval. This gives us tremendous resolution in reconstructing the specific environment inhabited by one of our early ape ancestors,” Dr McNulty explained.
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,” Dr Peppe said.
“During the dry season, there was probably relatively little rainfall. 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.”
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Lauren A. Michel et al. 2014. Remnants of an ancient forest provide ecological context for Early Miocene fossil apes. Nature Communications 5, article number: 3236; doi: 10.1038/ncomms4236
