A fossil from the gap
In 1982, a Joint Japan-Kenya Expedition was searching the Samburu Hills of northern Kenya. The team discovered a fossilized left maxilla, or upper jaw bone, complete with its postcanine teeth. Cataloged as KNM-SH 8531, the specimen belonged to a previously unknown genus of extinct ape. Researchers named it Samburupithecus kiptalami.
Radiometric dating of the geological formation where it was found, the Namurungule Formation, placed the fossil at approximately 9.5 million years old. This date places it squarely in the Late Miocene epoch, a period with a very sparse African hominoid fossil record sometimes called the "African ape gap," which lasted from about 14 to 7 million years ago. Before the discovery of Samburupithecus and a few other contemporary apes like Nakalipithecus, this period was a near-blank in the story of ape evolution in Africa.
A gorilla-sized fruit eater
The jaw of Samburupithecus indicates it was a large primate, estimated to weigh around 60 kilograms (130 lbs), comparable in size to a modern female gorilla. Analysis of its dental anatomy provides clues about its life. The molars are robust, with low, rounded cusps and a thick coating of enamel. This dental structure suggests a diet that included tough, fibrous vegetation and hard objects, a departure from the soft-fruit diet of many earlier apes.
Paleoenvironmental reconstructions show that 9.5 million years ago, this part of Kenya was a wooded habitat surrounded by savannah. The strong jaw and specialized teeth of Samburupithecus were well-suited for processing the challenging plant materials found in such an environment. Its cranial features, such as low, broad cheekbones and a large maxillary sinus, further distinguish it from other known Miocene apes.
The evolutionary position of Samburupithecus is still debated. Its unique mix of features has led to several hypotheses. Some scientists suggest it could be a common ancestor to gorillas, chimpanzees, and humans, living before that lineage split. Other analyses propose it may be a late-surviving member of an older group of stem hominoids. Regardless of its exact placement on the family tree, the fossil shows the ape diversity that persisted in Africa through a period of significant environmental change.