After an ‘interesting’ discussing last night I have tried to find the answer to the question ‘When did primates first appear?’ After reading wiki and a couple of other articles the following seems to encompass the latest perceived understanding. There is a bit here for all sides of the debate: – Deskarati
Many people take an understandably human-centered view of primate evolution, focusing on the bipedal, large-brained hominids that populated the jungles of Africa a few million years ago. But the fact is that primates as a whole–a category of megafauna mammals that includes not only humans and hominids, but monkeys, apes, lemurs, baboons and tarsiers–have a deep evolutionary history that stretches as far back as the age of dinosaurs.
The first mammal that palaeontologists have identified as possessing primate-like characteristics was Purgatorius, a tiny, mouse-sized creature of the late Cretaceous period (just before the K/T Impact Event that rendered the dinosaurs extinct). Although it looked more like a tree shrew than a monkey or ape, Purgatorius had a very primate-like set of teeth, and it (or a close relative) may have spawned the more familiar primates of the Cenozoic Era. (Genetic sequencing studies suggest that the earliest primate ancestor may have lived a whopping 20 million years before Purgatorius, but as yet there’s no fossil evidence for this mysterious beast.)
Recently, scientists have touted the equally mouse-like Archicebus, which lived 10 million years after Purgatorius, as the first true primate, and the anatomic evidence in support of this hypothesis is even stronger. What’s confusing about this is that the Asian Archicebus seems to have lived around the same time as the North American and Eurasian Plesiadapis, a much bigger, two-foot-long, tree-dwelling, lemur-like primate with a rodent-like head. The teeth of Plesiadapis displayed the early adaptations necessary for an omnivorous diet–a key trait that allowed its descendants tens of millions of years down the line to diversify away from trees and toward the open grasslands. Via Evolution – The Story of Prehistoric Primates.