Reconsidering the status and affinities of the ornithischian dinosaur Tatisaurus oehleri Simmons, 1965

The early Mesozoic fossil fauna collected from the Lower Lufeng Formation of Yunnan Province, China, has attracted considerable interest and attention since its discovery in the late 1930s. Its importance reflected a combination of its comparatively remote geographical position and, more particularly, the similarities of its fauna compared with approximately contemporary discoveries from Europe, North and South America, and southern Africa. The fragmentary and poorly preserved Lufeng ornithischian dinosaur Tatisaurus oehleri was described in 1965 and proved taxonomically and systematically enigmatic from the start. Originally assigned, with some noted ambivalence, to the basal ('primitive') group of ornithischians known as hypsilophodontids, since 1965 Tatisaurus has been variously ignored, assigned to a more rigorously defined Hypsilophodontidae, referred to both of the armoured (thyreophoran) ornithischian dinosaur clades (Stegosauria and Ankylosauria), or referred to a more basal position within the thyreophoran lineage. In 1996 the holotype of Tatisaurus was renamed Scelidosaurus oehleri, and the genus Scelidosaurus was proposed as an index fossil of the 'Scelidosaurus biochron' with the potential to be used for the global stratigraphic correlation of Early Jurassic (early Sinemurian) rocks. Because of this chequered history Tatisaurus oehleri Simmons, 1965 has been re-examined and is redescribed so that its taxonomic status and systematic position could be reassessed. Tatisaurus is identified as a basal thyreophoran (armoured ornithischian dinosaur); there is no basis for amalgamating it in synonymy with the genus Scelidosaurus, and the proposed creation of a 'Scelidosaurus biochron' for the purposes of biostratigraphic correlation of Lower Jurassic outcrops has no utility whatever. (c) 2007 The Linnean Society of London.