Ohio University-led scientists have uncovered fossils of two new species of ancient primates, named Rukwapithecus fleaglei and Nsungwepithecus gunnelli, which they say are the oldest paleontological evidence of split between Old World monkeys and apes.

Both species are new to science, and were collected from a single site in the Rukwa Rift Basin of Tanzania.

Geological analyses of the site indicate that the finds are 25 million years old, significantly older than fossils previously documented for either of two major groups of primates: the group that today includes apes and humans (hominoids), and the group that includes Old World monkeys such as baboons and macaques (cercopithecoids).

Rukwapithecus fleaglei, an early hominoid represented by a mandible preserving several teeth, and Nsungwepithecus gunnelli, an early cercopithecoid represented by a tooth and jaw fragment, lived 34 to 23 million years ago during the Oligocene epoch.

“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 Prof Nancy Stevens, lead author of a paper reporting the discovery in the journal Nature.

The study documents for the first time that the two lineages were already evolving separately during this geological period.

Prior to these finds, the oldest fossil representatives of the hominoid and cercopithecoid lineages were recorded from the early Miocene, at sites dating millions of years younger.

“The new discoveries are particularly important for helping to reconcile a long-standing disagreement between divergence time estimates derived from analyses of DNA sequences from living primates and those suggested by the primate fossil record,” Prof Stevens said.

“Studies of clock-like mutations in primate DNA have indicated that the split between apes and Old World monkeys occurred between 30 million and 25 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.”

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Bibliographic information: Nancy J. Stevens et al. Palaeontological evidence for an Oligocene divergence between Old World monkeys and apes. Nature, published online May 15, 2013; doi: 10.1038/nature12161