In 2011, a team of palaeontologists led by Nancy Stevens, unearthed a single molar in Tanzania’s Rukwa Rift Basin. It was a tiny fossil, but its distinctive crests, cusps and clefts told Stevens that it belonged to a new species. What’s more, it belonged to the oldest known Old World monkey—the group that includes modern baboons, macaques and more. They called it Nsungwepithecus.
A year later, and 15 kilometres away, the team struck palaeontological gold again. They found another jawbone fragment, this one containing four teeth. Again, a new species. And again, an old and distinctive one. The teeth represent the oldest fossils of any hominoid or ‘ape’. They called it Rukwapithecus.
Together, these two new species fill in an important gap in primate evolution. Based on the genes of living species, we know that Old World monkeys and apes must have diverged from each other between 25 and 30 million years ago. But until now, there weren’t any fossils from either group during that window. The ones we found were all 20 million years old or younger.
But Nsungwepithecus and Rukwapithecus were both found in sediments that could be precisely dated to 25.2 million years ago. They imply that apes had already split away from Old World monkeys by that time. Finally, fossils had corroborated the story that genes were telling. And they suggested that the split between these two groups took place against a backdrop of geological upheaval.
I wrote about the discoveries for The Scientist so head over there for the full story.