Researchers looking for fossils of early human ancestors at the Cradle of Humankind World Heritage Site in Malapa, South Africa, have unearthed the partial skull of the earliest baboon ever found. The 2-million-year-old fossil may represent the first appearance of modern baboon anatomy, according to findings published in PLoS One this week.
Just a few years ago, excavations at Malapa Cave yielded partial skeletons that belonged to Australopithecus sediba, an early hominin (that’s us and our extinct ancestors) that lived around 1.98 million years ago. "Baboons are known to have co-existed with hominins at several fossil localities in East Africa and South Africa," Hunter College’s Christopher Gilbert says in a statement. "They are sometimes even used as comparative models in human evolution." These days, baboons are a successful group of primates that live all across sub-Saharan Africa into the Arabian Peninsula. But despite this evolutionary success, their origins in the fossil record aren’t well understood (or agreed upon).
This newly discovered specimen, called UW 88-886, dates back 2.026 million to 2.36 million years, and it likely came from a male Papio angusticeps, a Plio-Pleistocene baboon that was first described in 1940. Importantly, it confirms that P. angusticeps is, in fact, closely related to a modern baboon species called Papio hamadryas. "If you placed a number of P. angusticeps specimens into a modern osteology collection, I don't think you'd be able pick them out as any different from those of modern baboons from East and South Africa," Gilbert says.
Furthermore, UW 88-886 represents the first appearance of modern baboon anatomy: a long, narrow muzzle and well-developed ridges on the upper jawbone, for example. And it coincides almost perfectly with previous estimates for the initial appearance of modern baboons. "According to molecular clock studies, baboons are estimated to have diverged from their closest relatives by ~1.8 to 2.2 million years ago," Gilbert says. "However, until now, most fossil specimens known within this time range have been either too fragmentary to be definitive or too primitive to be confirmed as members of the living species."
CT scans show UW 88-866 in oblique (left) and lateral (right) views. Wits University