Although not as long as the Paleozoic Era, the Mesozoic Era is the most popular era to have ever taken place. After surviving a mass extinction, the synapsids and the reptiles had eventually evolved into mammals and dinosaurs respectively. Both species started out small, but later in the Mesozoic, the dinosaurs had soon grown to large sizes, and started to show uniqueness in themselves. As well as this, a branch of small dinosaurs had soon evolved into birds. The mammals, on the other hand, stayed small for all of the period. After a golden age of land domination, a meteor had struck the Earth, causing another calamitous mass extinction and killing off most of the dinosaurs, leaving the mammals to rule the Earth.