Avisauridae leg formed by fused metatarsals (the bones which comprise the foot in humans). As a result, members of this family are distinguished from other enantiornitheans exclusively by features of the tarsometatarsal and pedal phalanges (toe bones). Unlike in some prehistoric birds, avisaurid tarsometatarsals were not completely fused, with the distal (outer) parts of the metatarsals being separate from each other. The proximal (near) half of metatarsal III (the long bone in the middle of the tarsometatarsus) is convex from the front. The inside edge of this bone's trochlea (toe joint) has a bony tab which points downward, known as a
Diandongosuchus The astragalus and calcaneum bones of the ankle fit together like a ball-and-socket, a feature that confirms "Diandongosuchus" as a pseudosuchian. Some of the phalanges or toe bones are missing in ZMNH M8770, but the metatarsals are present and have unique proportions among Triassic archosaurs in which the fourth is longer than the third. A phylogenetic analysis conducted by Li "et al." (2012) in the original description of "Diandongosuchus" showed that it was the most basal member of a clade called Poposauroidea, which includes mostly terrestrial pseudosuchians such as the bipedal "Poposaurus" and the sail-backed "Arizonasaurus". It was found to