Earliest colobine skeletons from Nakali, Kenya

Abstract

Old World monkeys represent one of the most successful adaptive radiations of modern primates, but a sparse fossil record has limited our knowledge about the early evolution of this clade. We report the discovery of two partial skeletons of an early colobine monkey (Microcolobus) from the Nakali Formation (9.8-9.9 Ma) in Kenya that share postcranial synapomorphies with extant colobines in relation to arboreality such as mediolaterally wide distal humeral joint, globular humeral capitulum, distinctly angled zona conoidea, reduced medial trochlear keel, long medial epicondyle with weak retroflexion, narrow and tall olecranon, posteriorly dislocated fovea on the radial head, low projection of the femoral greater trochanter, wide talar head with a greater rotation, and proximodistally short cuboid and ectocuneiform. Microcolobus in Nakali clearly differs from the stem cercopithecoid Victoriapithecus regarding these features, as Victoriapithecus is postcranially similar to extant small-sized terrestrial cercopithecines. However, degeneration of the thumb, a hallmark of modern colobines, is not observed, suggesting that this was a late event in colobine evolution. This discovery contradicts the prevailing hypothesis that the forest invasion by cercopithecids first occurred in the Plio-Pleistocene, and shows that this event occurred by the late Miocene at a time when ape diversity declined.

Early cercopithecid monkeys from the Tugen Hills, Kenya

“…Although early estimates of this site's age placed it between 8.5 and 10.5 Ma (7), our more recent radiometric dating narrows this range to between 8.8 and 9.5 Ma (4,6,15). Colobines are also known from the roughly contemporaneous site of Nakali, Kenya, at around 9.5 Ma (5, 22), where they appear to be represented by the same genus (5). Outside of Africa, the earliest colobine is Mesopithecus, which is found at several sites throughout Southern Europe between 8.5 and 6 Ma (1).…”

The latest occurrence of the nyanzapithecines from the early Late Miocene Nakali Formation in Kenya, East Africa

“…From the Nakali Formation, a considerable number of cercopithecoid fossils have been recovered. Many of them are a small (~4 kg) colobine Microcolobus (Kunimatsu et al, 2007;Nakatsukasa et al, 2010). This is not a dedicated folivorous primate, unlike living colobines (Benefit, 2000), and could have been a potential competitor for sympatric, small, non-cercopithecoid catarrhines.…”

“…The Kenya-Japan Joint Expedition to Nakali started new fieldwork in 2002 (Nakatsukasa, 2009). Since then, thousands of fossils including vertebrates and plant leaves have been recovered through surface collection and excavation (Kunimatsu et al, 2007(Kunimatsu et al, , 2016Nakatsukasa, 2009;Nakatsukasa et al, 2010;Handa et al, 2015;.…”

Molecular phylogeny and divergence time of <I>Trachypithecus</I>: with implications for the taxonomy of <I>T. phayrei</I>

“…The Homo-Pan divergence occurred between 7.2−5.6 Ma (Aiello & Collard, 2001;Senut et al, 2001), so we set the prior as lognormal and offset=5.6, SD =0.29. The oldest Colobinae was dated to 9.8 Ma (Benefit & Pickford, 1986;Nakatsukasa et al, 2010), but the molecular divergence estimation indicated a much more ancient divergence (Chatterjee et al, 2009), so we set the prior as exponential. The earliest possible age was set to 9.8 Ma, and the older 95% CI to 20 Ma (mean=3.4).…”