Which period marked the earliest part of the Mesozoic Era?

The Triassic period is recognized as the earliest part of the Mesozoic Era, which spans from about 252 million years ago to 66 million years ago. This period is significant because it follows the Permian period and features the emergence of distinctive reptilian life forms, including the first dinosaurs and the early ancestors of mammals.

During the Triassic, the Earth's continents were still in the process of breaking apart from the supercontinent Pangaea, leading to unique geological and climatic conditions. The ecosystems began to diversify, establishing a foundation for the later dominance of dinosaurs in the Jurassic and Cretaceous periods. The Jurassic came after the Triassic and saw the rise of diverse dinosaur species and more complex ecosystems. The Cretaceous followed the Jurassic and is noted for its flowering plants and further evolution of dinosaurs. The Permian, while significant, is part of the Paleozoic Era and precedes the Mesozoic, thus not applicable in this context.