Tatisaurus, SIMMONS, 1965

Norman, David B., Butler, Richard J. & Maidment, Susannah C. R., 2007, Reconsidering the status and affinities of the ornithischian dinosaur Tatisaurus oehleri Simmons, 1965, Zoological Journal of the Linnean Society 150 (4), pp. 865-874 : 871

IS TATISAURUS A STEGOSAUR?

Dong (1990) suggested that Tatisaurus is a primitive member of the clade Stegosauria, and referred it to the family Huayangosaurinae . He did not provide explicit synapomorphies as a basis for this assignment, but suggested that the general features of the teeth were ‘similar’ in Tatisaurus and Huayangosaurus . As discussed above, the general morphology of the dentary teeth of Tatisaurus is not known (despite statements to the contrary): only the most general of features are apparent and these are widespread within basal ornithischians. Any supposed similarity between the teeth of Tatisaurus and Huayangosaurus would, at best, be the result of retained plesiomorphies, rather than shared derived characters. Some features can be identified that distinguish Tatisaurus and Huayangosaurus : the ventral margin of the mesial end of the dentary is inturned to a much greater degree in Huayangosaurus ( Sereno & Dong, 1992: fig. 5D) than in Tatisaurus ; the predentary of Huayangosaurus has a narrow and elongate ventral process, whereas there is little evidence for the presence of a predentary with an extensive ventral process in Tatisaurus (see above); and the dentary tooth count is considerably higher in Huayangosaurus than in Tatisaurus . No synapomorphies can be identified that unite Tatisaurus with either Huayangosaurus or other stegosaurs, to the exclusion of other ornithischians. We therefore consider that the assignment of Tatisaurus to Stegosauria ( Dong, 1990) is unsupported.