Dianopachysaurus is an extinct genus of pachypleurosaur known from the lower Middle Triassic (Anisian age) of Yunnan Province, southwestern China. It was found in the Middle Triassic Lagerstätte of the Guanling Formation. It was first named by Jun Liu, Olivier Rieppel, Da-Yong Jiang, Jonathan C. Aitchison, Ryosuke Motani, Qi-Yue Zhang, Chang-Yong Zhou and Yuan-Yuan Sun in 2011 and the type species is Dianopachysaurus dingi, thanking a Professor Ding for his help.[1]
Dianopachysaurus is most closely related to Keichousaurus, another Chinese pachypleurosaur. Both belong to the family Keichousauridae. Pachypleurosaurs are hypothesized to have originated in the eastern Tethys Ocean (South China) before spreading and diversifying in the western Tethys in what is now Europe. A large ghost lineage of eastern pachypleurosaurs has long been inferred based on the phylogeny of the group. Dianopachysaurus represents an early stage in the radiation of pachypleurosaurs and its early age fills in much of the gap.[1]
The holotype, and only fossil so far, is an almost complete articulated skeleton. It measured 14.3 cm (5.6 in) long from nose tip to the last caudal vertebra known, although the end of the tail is missing after the 17th caudal vertebra.[1] It is estimated to have measured about to 20 cm (7.9 in) in total body length.[2]