An 18-million-year-old ape with no tail. The oldest evidence of the body plan that would eventually produce humans and chimpanzees.
Guérin Nicolas (messages), CC BY-SA 3.0, via Wikimedia Commons
An ancestor in a volcano's shadow
On Rusinga Island, located in Kenya's portion of Lake Victoria, paleontologist Mary Leakey made a remarkable discovery in 1948. She uncovered the fossilized skull of a primate that lived approximately 18 million years ago, during the Miocene epoch. The specimen, designated KNM-RU 7290, was the most complete skull of Proconsul ever found. This individual lived and died in a dense tropical forest on the slopes of an active volcano, whose periodic ashfalls helped preserve its remains.
The genus Proconsul first came to light from a partial jaw found in 1909 at Koru, not far from Rusinga Island. Paleontologist Arthur Hopwood named the genus in 1933. The name means "before Consul," referencing a popular performing chimpanzee in London at the time. Mary Leakey's later discovery provided an unprecedented look at the complete head of this early primate. The skeleton itself is now housed at the National Museums of Kenya in Nairobi.
A mosaic of features
Proconsul africanus presents a mix of anatomical traits linking it to both Old World monkeys and the first apes. Its skeleton suggests it was an arboreal quadruped, moving about on all fours along tree branches. Its wrist and limb proportions were monkey-like. Its shoulder and elbow joints were more flexible, similar to those of modern apes. The dental formula is 2.1.2.3, and the molars have thin enamel, indicating a diet of fruit. The species had an estimated body mass of around 18 kilograms (40 pounds) and a cranial capacity of about 167 cubic centimeters.
The most important feature of the Proconsul body plan is what it lacks: a tail. Analysis of the sacral vertebrae confirms there was no tail, a defining characteristic that separates apes and humans from most monkeys. This combination of monkey-like and ape-like features records an early stage in the evolution of hominoids, the superfamily that includes gibbons, great apes, and humans.
💡Fun Facts
The genus name *Proconsul* does not refer to a Roman official, but to a famous circus chimpanzee named Consul that performed in London in the early 20th century.
The 1948 skull was so complete because it was found inside the fossilized trunk of a hollow tree.
Although often referred to as *Proconsul africanus*, paleontologist Alan Walker reclassified the famous 1948 skeleton as *Proconsul heseloni* in 1993.
Rusinga Island has yielded thousands of *Proconsul* fossils, making it one of the most important sites for understanding early primate evolution.
The original fossil is in the Nairobi National Museum, open daily 8:30 AM - 5:30 PM. The discovery site on Rusinga Island is an open archaeological area with no fixed hours, best visited by local arrangement.
Admission
The Nairobi National Museum has an admission fee for non-resident adults and children. Accessing the Rusinga Island sites may require hiring a local guide.
Accessibility
The Nairobi National Museum is wheelchair accessible. The terrain on Rusinga Island is rugged and uneven; visiting the fossil sites requires walking over unpaved ground.
