“…In general, the Leonardian regional stage is less known than the other Permian stages in the USA (Dunbar et al, 1960;Ross, 1960Ross, , 1962Ross, , 1986Ross, , 1995Magginetti et al, 1988;Fichten et al, 1995;Davydov, 1996;Davydov et al, 1997;Ross and Ross, 2003;Stevens and Stone, 2007); and in all of the Americas (Johnson and Kaska, 1965;Pérez-Ramos, 1992;Vachard et al, 1997;2000a, 2000b, 2000cGroves, 2000;Pérez-Ramos and Nestell, 2002). The equivalents of the Leonardian are the Artinskian and Kungurian of the Ural Mountains in Russia (e.g., Chuvashov et al, 1990;Anfimov et al, 1991); two stages which are now the international references in chronostratigraphy.…”