has a form unlike the vertebrae of these archosauriforms, and Nesbitt concluded that it was an 'insertion', formed from the innermost sections of the two primordial vertebrae. Although this process is not unique to poposauroids, it is only known in a few other archosaur lineages, such as Batrachotomus, silesaurids, and dinosaurs. Basal poposauroids such as Arizonasaurus and Qianosuchus only had three sacral vertebra, with the second vertebra being the 'insertion'. However, more advanced poposauroids such as Poposaurus and shuvosaurids have four sacral vertebrae, with the third vertebra being recognizable as the 'insertion'. This means that the first vertebra must have been another addition, seemingly the last dorsal vertebra which had been repurposed and transformed into a sacral vertebra. This incorporated dorsal vertebra is known as a 'dorsosacral'. The presence of dorsosacrals is a trait with an irregular distribution among archosaurs, being known in a few ornithosuchids and aetosaurs as well as a variety of dinosaurs (most commonly in ornithischians and theropods) In almost all archosariforms, the sacral ribs of the first 'primordial' sacral vertebra contact the ilium near the base of that bone, close to its contact with the pubis. However, poposauroids have first 'primordial' sacral ribs with additional forward branches, which lie on the inner edge of the ilium's preacetabular blade. In poposauroids more advanced than Qianosuchus, the sacral vertebrae fuse into a single bone, the sacrum. This fusion occurred incrementally, at different portions of the vertebra. For example, the zygapophyses fused together as early as the ctenosauriscids. The centra (main cylindrical portion) of the sacral vertebrae also may have fused as early as the ctenosauriscids. The bases of the neural arches (the portion of the vertebrae above the spinal cord) were fused in some ctenosauriscids (Arizonasaurus) but not others (Bromsgroveia), and were also fused in all poposauroids more advanced than the ctenosauriscids. Other features Unlike most pseudosuchians, poposauroids lack bony scutes known as osteoderms. The only exception to this is Qianosuchus, which possessed numerous tiny osteoderms, lying in a row extending down the neck and body. In all poposauroids, the tip of the fibula (outer shin bone) is symmetrical and straight when seen from the side, rather than slanted as in other non-crocodylomorph pseudosuchians. Poposauroids more advanced than ctenosauriscids had flattened, "hoof-like" pedal unguals (toe claws). Some poposauroids had very short arms compared to the length of their legs, although disarticulation in Qianosuchus and a lack of limb