By the midtwentieth century most scientists shared the view that the primate order consisted of the living and fossil tree shrews, lemurs, galagos, lorises, tarsiers, monkeys, and apes, including humans. The fossils of three extinct radiations known primarily from the Paleocene and Eocene of western Europe and North America were also included: the Plesiadapiformes (sometimes referred to as Archaic Primates), the Adapiformes, and the Omomyiformes. Primates were seen as the archetypal arboreal mammals and were consequently thought to have evolved most of their characteristics as a direct result of the demands of arboreal life.