Hominids – What preceded?
The earliest primates likely descended from a small, nocturnal, insectivorous mammal. The tree shrews and colugos (also known as flying lemurs) are the closest living relatives to primates. The tree shrew is used as a living model for what the earliest primates, or primate predecessors, might have been like. At some point, primates or their ancestors moved into the trees and adapted to an arboreal environment. Two theories regarding the evolution of some primate characteristics, such as grasping or prehensile hands, forward-oriented eyes, and depth perception, are the Arboreal and Visual Predation Theories. The Arboreal Theory posits that primate characteristics, such as grasping hands and feet and the presence of nails instead of claws, are the result of moving into and adapting to an arboreal environment. (Imagine the casualties!) The Visual Predation Theory asserts that characteristics that were well-suited to scurrying around in trees and visual features in particular, such as convergent orbits, are adaptations to insect predation. Short of a butterfly net, grasping hands, visual acuity, and depth perception are essential for catching insects, but I guess they would be kind of handy for using a butterfly net as well!
While we have no primate fossil material prior to the Eocene Epoch, the first primates are thought to have evolved prior to the Paleocene Epoch (66–56 mya), possibly as far back as 90 mya, during the Late Cretaceous Period. With the extinction of the dinosaurs at the end of the Cretaceous, many terrestrial niches became available and predation pressures were somewhat relaxed.
Lemurs, primates belonging to the suborder Strepsirrhini which branched off from other primates less than 63 million years ago, evolved on the island of Madagascar, for at least 40 million years. They share some traits with the most basal primates, and thus are often confused as being ancestral to modern monkeys, apes, and humans. Instead, they merely resemble ancestral primates.