Evolution: Fossils Pinpoint Ape and Monkey Split
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In the past, DNA analysis has offered scientists clues to a specific period in which monkeys and apes diverged on the evolutionary timeline, however, a recent discovery in Tanzania may be the solid evidence they have been searching for, according to researchers.
The oldest ape and Old World monkey fossils have been discovered, as scientists unearthed a tooth and a jawbone in a riverbed that date back 25 million years. At the time, there were two distinct major groups of primates, including one that featured apes and another that featured Old World monkeys such as baboons and macaques.
"These discoveries are important because they offer the earliest fossil evidence for either of these primate groups," said lead study author Nancy Stevens, an anthropologist at Ohio University in Athens, Ohio.
DNA evidence has long suggested that apes and monkeys diverged between 25 to 30 million years ago, but no fossils had been discovered older than 20 million years in age.
"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.
The jawbone discovered belongs to a new species named Rukwapithecus fleaglei, which was an early hominid (a group that contains the great apes, including gorillas, chimpanzees, bonobos, orangutans and humans and lesser apes such as gibbons). The tooth belonged to another newfound species called Nsungwepithecus gunnelli, which is the oldest known member belonging to the group that contains Old World monkeys called cercopithecoids. The primates lived during the Oligocene epoch, which lasted from 34 to 23 million years ago.
The new research documents a period in which the species were already evolving separately.
"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 Stevens.
"Finding monkey and ape fossils of this age in Africa has been extremely difficult, but to find both branches in a well-dated fossil layer this old is extraordinary," said Paul Filmer, program director in NSF's Division of Earth Sciences.
"These 'oldest-yet' fossils reinforce that the Old World monkey and ape branches were already separate 25 million years ago."
Researchers estimate that Rukwapithecus weighed about 26 lbs. and Nsungwepithecus is estimated to have been slightly smaller.
The team's findings were published in the journal Nature.