21-million-year-old spine showing early adaptation for vertical climbing. The oldest evidence of the body plan that would lead to upright walking.
Ghedoghedo, CC BY-SA 3.0, via Wikimedia Commons
The first upright ape
In the semi-arid Karamoja region of northeastern Uganda, paleontologists uncovered fossils that rearrange the timeline of ape evolution. The remains belong to Morotopithecus bishopi, a large-bodied ape that lived at least 20.6 million years ago. The important fossils are several vertebrae, including a well-preserved lumbar vertebra cataloged as UMP 67-28. Analysis of these bones shows anatomical features previously thought to have appeared millions of years later.
The lumbar vertebrae of Morotopithecus have a shape and structure remarkably similar to those of modern great apes and humans. Specifically, the bony projections on the side of the vertebra, called transverse processes, are positioned on the dorsal side (the back), which allows for a stiff and stable lower back. This spinal rigidity is an adaptation for an orthograde, or upright, posture. It contrasts with the more flexible spines of monkeys and earlier primates like Proconsul, which were primarily quadrupedal. The find suggests that the modern hominoid body plan, which would eventually lead to human bipedalism, appeared much earlier than previous evidence indicated.
Life in a changing world
The fossils of Morotopithecus were found near the remnants of an ancient volcano in sediment layers dated using the 40Ar/39Ar method on overlying basalt. Along with the spine, researchers have found parts of a shoulder blade, two partial femurs, and craniodental remains. The shoulder joint appears adapted for suspension, while the femur suggests a mix of climbing and quadrupedal movement. This combination indicates a versatile climber, capable of moving through trees using its forelimbs and maintaining an upright posture.
Studies of the paleoenvironment show that Morotopithecus did not live in a dense, continuous-canopy forest. Instead, it inhabited a seasonally dry woodland with open, grassy areas. This environment experienced periods of water stress, meaning fruit was not always available. Analysis of Morotopithecus molars, which are suited for shearing tough vegetation, suggests its diet consisted mainly of leaves. This evidence challenges the theory that apes evolved upright postures to access fruit on the outer branches of trees. Instead, an upright stance may have helped Morotopithecus forage for leaves in a more open, varied habitat.
💡Fun Facts
The species name "*bishopi*" honors W. W. Bishop, a British geologist who pioneered paleontological research in Uganda in the 1960s.
The first key fossil specimen, a palate with teeth known as UMP 62-11, is the "holotype" that officially defines the species.
Analysis of fossil soils and plant silica particles (phytoliths) from the Moroto II site provided the first evidence of C4 grasses in Africa, pushing back their appearance by over 10 million years.
The femur of *Morotopithecus* has unusually thick cortical bone, suggesting it withstood higher physical loads than most living primates.
This is an active and remote paleontological site with no public access or facilities.
Admission
N/A
Accessibility
The fossil sites are in a remote, rugged, and semi-arid region requiring expedition-level planning and permissions from local authorities and the Uganda Museum. Travel is by 4x4 vehicle over difficult terrain.
