Etymology- Oshan is a variant of Eshan, a county in Yunnan it was found in. The species name probably references famed Chinese paleontologist Young Zhongjian.
Hettangian, Early Jurassic
Zhangjiawa Member of the Lufeng Formation, Dianchung, Eshan County, Yunnan, China
|Holotype anterior mandible of Eshanosaurus deguchiianus (IVPP V11579) in medial (A), dorsal (B) and lateral (C) views, and tooth in lingual (D), labial (E) and distal (F) views (after Xu et al., 2001). Is this "Oshanosaurus youngi"?|
Comments- Glut (1997) incorrectly stated it was found in Mongolia. I suspect this is an old name for Eshanosaurus, which has the same etymology, is also from the Dianzhong Basin of Eshan County, was discovered by Zhao in 1971 and was later described in part by him (Zhao and Xu, 1998; Xu et al., 2001).
Relationships- Stated by Zhao (1985) to be a primitive sauropod. Chure and McIntosh (1989), Lambert (1990) and provisionally Olshevsky (1991) listed it as a cetiosaurid. Glut (1997) listed it as a possible heterodontosaurid or "geranosaur", possibly because Zhao mentions it in the same sentence as Dianchungosaurus. As traditional Cetiosauridae now refers to a grade of basal eusauropods, ignoring the Eshanosaurus connection I would retain "Oshanosaurus" as Sauropoda incertae sedis.
While Eshanosaurus is corrently believed to be a therizinosaur, therizinosaur mandibles are quite similar to those of sauropodomorphs and were poorly known in the 1980s. Indeed, Eshanosaurus' mandible resembles those of basal eusauropods (e.g. Shunosaurus) more than basal sauropodomorphs in having a dorsoventrally expanded symphysis, anterior teeth the largest, a basolingual swelling on its teeth, a lingual median ridge on its teeth, and tooth roots expanded to be broader than their crowns. However, it is unlike eusauropods in having a narrow symphysis, smooth enamel, a lateral dentary ridge and perpendicular serrations on its teeth. Given Eshanosaurus' similar incongruity when considered as a therizinosaur (more derived than the much later Falcarius in having a decurved symphysis, lateral ridge and enlarged serrations; not to mention early appearence compared to other coelurosaurs), it may be convergent with both eusauropods and therizinosaurs.
References- Zhao and Xu, 1998. The oldest coelurosaurian. Natrure. 394, 234-235.
Xu, Zhao and Clark, 2001. A new therizinosaur from the Lower Jurassic Lower Lufeng Formation of Yunnan, China. Journal of Vertebrate Paleontology. 21(3), 477-483.