A late Permian archosauriform from Xinjiang shows evidence of parasagittal posture

Archosaurs diversified and became dominant during the Mesozoic Era, but their earliest relatives (non-archosaurian archosauromorphs) were already scarcely present in the late Permian. Here we describe a new species of non-archosaurian archosauriform from the upper Permian of Xinjiang, China. Preserved as a partial hindlimb, it possesses a few derived features shared with other archosauriforms, including a much stouter tibia than fibula, a longer metatarsal III than metatarsal IV, and a hooked metatarsal V. Phylogenetic analysis confirmed the new taxon to be a non-archosaurian archosauriform. The morphology of the knee, crus, and pes shows traits that are commonly related with a parasagittal posture, including an entirely proximo-distal articulation of the femur and fibula, the slender and closely spaced tibia and fibula, and a mesaxonic foot with a reduced fifth toe. The new taxon shows that the parasagittal posture evolved before the end-Permian Mass Extinction.