Swift thecodonts,the ancestors of dinosaurs,scampered along the upland.Herds of mammal-like reptiles grazed on cycads and horsetails.By the late Triassic the archosaurs had given rise to the first dinosaurs, and herds of plateosaurs roamed the uplands.Some evolutionarily advanced mammal-like reptiles evolved into true mammals,which were to remain small and inconspicuous for another 125 million years.