The osteology of the wrist of Heyuannia huangi (Oviraptorosauria) and its implications for the wrist folding mechanism.

The wrist of extant birds is highly specialized which permits folding of the forelimb in order to protect the pennaceous feathers when they are relaxed. This mechanism is absent in most non-avian theropods and is unknown in oviraptorosaurs because of the rarity of the specimens with well-preserved wrist. Here we give a detailed description of the wrist of two three-dimensionally preserved oviraptorosaurian Heyuannia huangi specimens from the Upper Cretaceous in Southern China. Heyuannia huangi possesses a highly specialized wrist with a strongly dorsoventrally compressed distal ulna, a larger radiale angle and a strongly convex semilunate carpal. The morphology of its wrist suggests that the distal ulna would not hinder the rotation of the manus, resulting in the smallest angle between the manus and the ulna being less than 90 degrees. The combination of the morphology of the wrist of oviraptorosaurs and the phylogenetic result indicates functional convergence in the wrist of oviraptorids and extant birds. [ABSTRACT FROM AUTHOR]