May 16, 2013
Oldest Evidence Of Split Between Monkeys And Apes Discovered
Brett Smith for redOrbit.com - Your Universe Online
The two primate fossils are from the late Oligocene epoch, about 25 million years ago, which is considerably older than previously discovered fossils for either group. The study authors conclude that the two groups of primates were already diverging at this time.
"The late Oligocene is among the least sampled intervals in primate evolutionary history, and the Rukwa field area provides a first glimpse of the animals that were alive at that time from Africa south of the equator," said lead author Nancy Stevens, an associate professor of paleontology at Ohio University.
The team was able to recover a single tooth and a jaw fragment with three teeth from a site in the Rukwa Rift Basin in southwestern Tanzania. They determined that the single tooth had nine characteristics that distinguished it from other Old World monkeys and belonged to a species that they dubbed Nsungwepithecus gunnelli. The jaw segment also had nine unique characteristics that set it apart from a class of primates that includes Old World monkeys and apes. They named that species Rukwapithecus fleaglei.
A lack of fossil-bearing rock strata of the appropriate age has made finding fossils like these difficult, Stevens explained. The team was able to accurately date the fossils by determining the age of multiple minerals contained within the rocks.
The new finds predate previous fossils that were discovered at early Miocene sites dating millions of years younger. They also help to resolve theories based on 'molecular clocks' – or mutations in DNA that can be used to estimate how long ago two species diverged. Using molecular clock models, previous theories have suggested that Old World monkeys and apes diverged from a common ancestor 25 million to 30 million years ago.
"Fossils from the Rukwa Rift Basin in southwestern Tanzania provide the first real test of the hypothesis that these groups diverged so early, by revealing a novel glimpse into this late Oligocene terrestrial ecosystem," Stevens said.
For their study, the team used Ohio University's MicroCT scanner, which allowed them to recreate detailed 3-dimensional images of the fossil specimens.
"This is another great example that underscores how modern imaging and computational approaches allow us to address more refined questions about vertebrate evolutionary history," said co-author Patrick O'Connor, a professor of anatomy at Ohio University.
The authors also noted the interdisciplinary nature of the research team, which included paleontologists and geologists — emphasizing that their teamwork allowed for a more complete picture of vertebrate evolutionary history.
"Since its inception this project has employed a multifaceted approach for addressing a series of large-scale biological and geological questions centered on the East African Rift System in Tanzania," O'Connor said.