Sacisaurus agudoensis (Ferigolo and Langer et al. 2006) Carnian, Late Triassic period, ~225 mya, 1.5 m in length, was considered one of the oldest dinosaurs yet found. It nests as a basal poposaurid, descended from a sister to Turfanosuchus and Poposaurus. Sacisaurus was basal to Silesaurus, Lotosaurus, Shuvosaurus and Effigia.
The skull was smaller than in more basal poposaurs. The mandible includes paired predentary bones at the tip. These converge with the single bone of ornithischians. The teeth have a smaller "neck" and an expanded crown. The large postorbital indicates a larger orbit.
Only one cervical is known and it had a parallelogram-shaped centrum for an elevated skull. The distal caudals were elongate as in Poposaurus. The scapula was elongate. The ilium was posteriorly extended more than in other poposaurs. The hind limbs were robust.