Following the extinction of the reptilian (diapsid lineage) dinosaurs, around 66 mya, and closer to 56 mya, there survived small, nocturnal mammals, the tree shrews (order Scandentia).

There then followed what may be considered the most primitive of early primates, the plesiadapiforms (e.g., Carpolestes simpsonii, an extinct, insectivore, with an abducted hallux and nail (instead of claw), allowing for arboreal grasping), also represented by Dromomys szalayi (National Geographic News, 2007), one of the earliest primate fossil remains, and possibly the last common ancestor (LCA) to modern primates, based on its pattern of molar teeth, suggestive of a diet of fruit and insects, and grasping hands and feet, to facilitate tree-living.

However, with no orbital convergence, no leaping, small brains, and with growing incisors and loss of canine teeth, this group diverged away from modern primates.

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These earliest of primates probably co-evolved with flowering plants and trees, in a world characterized by tropical and semi-tropical climates, even at the poles.