Youngoides UC 1528

Youngoides romeri FMNH UC1528 (Olson and Broom 1937) Late Permian, Wuchiapingian, ~255 mya was derived from a sister to Youngina AMNH 5561 and preceded Youngoides RC91 and Proterosuchus at the base of the pseudarchosauriformes and the Eurchosauriformes respectively.

Distinct from AMNH 5561, the skull of UC1528 had smaller temporal fenestrae and more robust bones surrounding it. The squamosal and quadrate lean anteriorly. The frontal has no posterior processes. The teeth are small, narrrow and recurved. The deepest curve on the mandible was further to the rear. The pineal foramen is tiny. The premaxilla is unknown, but considering the positions of the maxilla and dentary, the premaxilla had to overhang in the manner of Proterosuchus.

All prior workers considered Chanaresuchus and Proterosuchus to be in the same clade, the Archosauriformes. While true to a certain extent, (with FMNH UC 1528 as their last common ancestor) these two are here nested in two distinct clades, the pseudarchosauriformes and the Euarchosauriformes and both are derived from the basal Protorosauria and a series of Youngina with distinct morphologies.