Increased volcanism to the west provided a source of silica for permineralization of fossil wood. Climate had become more humid. B. Depositional environment broad, low, alluvial plain. Drained by slow rivers arid conditions evidenced by Moenkopi lagoons with salt, anhydrite, and gypsum formation. Conifers and cycads dominant, flowering plants appear.
Ammonites recover from near extinction and become important guide fossils.
First dinos appear. Many reptile types present. Amphibians continue to decrease in number, though some of the largest ones occurred during this period. First true mammals appear in the upper Triassic. I. Plate Tectonics and Paleogeography .