Summary

1. Eck & Jablonski (1984, 1987) have argued that the holotype crania of Papio baringensis (from the Chemeron Formation) and Papio quadratirostris (from the Omo Usno Formation) are actually specimens of Theropithecus which represent early stages of the T. brumpti lineage. These fossils are among the oldest members of the African Papionini which can be allocated to modern genera – the Usno Formation dates to about 3.4 Ma, while the Ghemeron Formation is probably slightly younger, although its age is less definitely known.

2. Despite many morphological studies to the contrary, but in line with a variety of molecular analyses, we accept Papio (including Mandrillus as a subgenus) as the closest known relative of Theropithecus among the African Papionini. A mandrill-like cranial morphology (with relative lack of klinorhynchy even with a long face; only moderately deep midface; extended or ‘pointed’ rather than rounded external occipital protuberance; bulbous, not high-crowned, molars; large front teeth; and ovoid, closely-spaced orbits) is hypothesized to be close to the ancestral morphotype of the baboon–mandrill–gelada clade. Within Theropithecus, there are three major lineages: T. gelada, T. oswaldi (and almost surely T. darti) and T. brumpti. Based on previous research by others, we take as a working hypothesis the closer phyletic relationship of the first two contrasted with T. brumpti.

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