The ape in our genes: on the place of humans in the natural order. Precambrian era: 4-2. 5 billion years ago. Rise of prokaryotes: 2. 5 billion-570 million years ago. The cambrian explosion: multi-celled lifeforms proliferate, ordovician period. First true fish evolve: silurian period. First plants and insects occupy terrestrial ecosystems: devonian period. First true reptiles evolve: permian period. Mass extinctions: 90% of all lifeforms die out. Earliest mammals and birds evolve: jurassic period. Dinosaurs predominate until mass extinctions: 70% of lifeforms die out. Modern mammalian groups adaptively radiate only after the extinction of the dinosaurs. Fossil evidence of nonhuman primates is associated with deposits dating from the tertiary period which began about 65 million years ago. However reconstructions of primate phylogeny based on genetic data suggest the earliest primates may have evolved as early as 80-90 million years ago in the late cretaceous period.