noting or pertaining to a period of the Mesozoic Era, occurring from 230 to 190 million years ago and characterized by the advent of dinosaurs and coniferous forests.
1841, from Ger., coined 1841 by Ger. geologist Friedrich August von Alberti (1795-1878), from Gk. trias "triad," because it is divisible (in Germany) into three groups.