What countries were the earliest and morphologiclly most primitive dinosaurs found?

The earliest and morphologically most primitive dinosaurs, such as the theropod and sauropodomorph groups, were primarily discovered in regions that were part of what is now Argentina and South Africa. These countries are significant due to their geological formations from the Late Triassic period, which provided the necessary conditions for fossil preservation. Notable examples include Eoraptor from Argentina and Herrerasaurus from the same region, as well as early dinosaur fossils found in South Africa's Karoo Basin.