A paleoecological model for the origin of higher primates

Tertiary climatic oscillations initiated the origin of anthropoid primates. A paleoecological model of anthropoid evolution is presented which assumes increasing global seasonality in the late Eocene. Size changes are effected to stabilize internal temperature fluctuations under cooler climatic conditions. Because larger body size is associated with diurnality and reduced litter size, these anthropoid behavoral and reproductive features also fit into the model. Dietary changes involving an emphasis on frugivory, which becomes a more predictable dietary mode under seasonal conditions, can be associated with the development of a post-orbital septum, a broad mesiodistal incisal span, the evolution of color vision, reduction of the olfactory bulbs, and the concomitant enlargement of areas of the brain relating to the processing of visual information. Finally, postural behavior or locomotion might be included in this model if frugivorous foraging and feeding behavior led to the development of a basic level of anthropoid locomotor morphology, involving adaptations for arboreal quadrupedalism.