When Notobatrachus degiustoi was discovered, a very important step in the history of the order Anura was filled with that find, the first record of the true frogs in the world was established in the Dogger of Patagonia. Now, the author presents a new evidence which makes much older the known record of the Anura. An impression of a frog has just been found in the Province of Santa Cruz (Patagonia) in beds (Roca Blanca formation) dated as Liassic and clearly lower than the Matilde formation, in which the Notobatrachus had been found. The new Liassic frog, which is refered to a new genus and species, Vieraella herbstii, is a small, very _primitive one, with at least eight presacrals vertebrae, free ribs, ulna and radius not fused, bony skull with some discoglossid characters. Sacrum, pelvis and urostyle are not known, and neither the character of the shoulder girdle nor the vertebral centra are known, as the only known impression is dorsal. Vieraella may be an Amphicoela or an Archaeobatrachia of the author's suborders, but more careful comparisons and new specimens are needed to determine accurately its systematic position. This new discovery strenghthens the significance that the find of Notobatrachus bore on the problems of Anuran biogeography.