Into the Light: The Origin of Anthropoidea

Anthropoidea is a clade of primates including Platyrrhini and Catarrhini. Definitive fossil anthropoids include the early Oligocene Propliopithecidae and the late Eocene–early Oligocene Parapithecidae and Oligopithecidae. Middle Eocene Eosimiidae are probable fossil anthropoids from Asia. Relationships of anthropoids to other primates are debated, although parsimony argues for a tarsier-anthropoid clade (Haplorhini) arising within omomyiforms. Distinctive features of the anthropoid visual system related to diurnality include highly convergent orbits, small corneal diameter/posterior nodal distance, high concentrations of cones and ganglion cells, and extreme magnification of foveal and parafoveal regions of the visual field in the visual cortex. Anthropoid origins was associated with a shift from a nocturnal visually predatory ancestor to diurnal visual predation at small body size (<100 g). This shift may have occurred in the stem lineage of the tarsier-anthropoid clade. The early anthropoids were insectivore-frugivores with unfused mandibular symphyses, small brains, and either dichromatic or trichromatic vision. The evolution of larger brains, symphyseal fusion, and definitive trichromacy occurred later in anthropoid evolution.