Earliest colobine skeletons from Nakali, Kenya

Area of Science:

• Paleontology
• Primate Evolution
• Paleoanthropology

Background:

• Old World monkeys are a successful primate radiation, but their early evolution is poorly understood due to a limited fossil record.
• Understanding early cercopithecid diversification is key to primate evolutionary studies.

Purpose of the Study:

• To describe new early colobine monkey fossils from Kenya.
• To reconstruct the early evolutionary history and ecological adaptations of Old World monkeys.

Main Methods:

• Analysis of two partial skeletons of Microcolobus from the Nakali Formation (9.8-9.9 Ma).
• Comparative analysis of postcranial skeletal features with extant colobines and other cercopithecoids.
• Reconstruction of arboreal adaptations based on skeletal morphology.

Main Results:

• Microcolobus fossils exhibit postcranial synapomorphies indicative of arboreality, shared with extant colobines.
• These features distinguish Microcolobus from Victoriapithecus, which is more similar to terrestrial cercopithecines.
• Degeneration of the thumb, characteristic of modern colobines, was not observed, suggesting it evolved later.

Conclusions:

• The discovery of arboreal Microcolobus in the late Miocene challenges the hypothesis of a Plio-Pleistocene forest invasion by cercopithecids.
• This indicates that forest specialization in cercopithecids occurred earlier, coinciding with a decline in ape diversity.