Theropithecus brumpti is the most abundant primate species in the fauna in the Turkana Basin between 3.5 and 2.5 million years ago. It probably inhabited the closed woodlands and forests and had a diet that included some grass but also other plants and fruit.
Theropithecus brumpti can be distinguished from Theropithecusoswaldi by its more elongate muzzle. It has expanded zygoma (the protuberances from the skull near the ear) and has a distingtive zygomatic arch, the ridge that runs along the top of the skull, that is triangular in cross section. Theropithecus brumpti also has larger incisors than found in the later Theropithecus oswaldi which replaced it at some point between 2.5 and 2. million years. Theropithecus oswaldi was a committed grazer which inhabited more open country.