Australian Cretaceous ichthyosaur material is amongst the most complete in the world. This study describes postcranial remains referred to the upper Albian species Platypterygius australis, including the first record of pelvic and hind limb elements for this taxon. A combination of phylogenetically significant traits such as lack of fusion between the atlas-axis complex and third cervical centrum, the presence of three distal facets on both the humerus/femur for accommodation of the anterior zeugopodial elements plus the radius/tibia and ulna/fibula, concave preaxial accessory facet surfaces on both the humerus and the femur, and complete fusion of the ischiopubis with closure of the obturator foramen, are considered diagnostic for the species and (in conjunction with other previously identified cranial/postcranial features) may serve to distinguish P. australis from the other paleogeographically disparate Platypterygius spp.