Tectonic plate subduction along western North America causes the Earth's crust to fold, and mountains form in the western part of the continent. Reptiles adapt to life in the sea, in the air, and on land. Dinosaurs are the dominant reptile on land. Archaeopteryx , the first bird, appears. Early amphibians, extinct by the Late Triassic, are succeeded by the first frogs, toads, and salamanders.
Mammals are small, shrew-like animals.
Plant forms are dominated by the cycads and cycadeoides. Conifers and gingkoes are widespread. The continents, while not in their current positions on the Earth, are shaped much as they are today. South America and Africa separate, and the North Atlantic ocean widens. The westward movement of North America forms the ancestral Rocky Mountains and the ancestral Sierra Nevada.