A revision of the Upper Triassic ornithischian dinosaur Revueltosaurus, with a description of a new species.

Ornithischian dinosaur body fossils are extremely rare in Triassic rocks worldwide, and to date the majority of such fossils consist of isolated teeth. Revueltosaurus is the most common Upper Triassic ornithischian dinosaur and is known from Chinle Group strata in New Mexico and Arizona. Historically, all large (>1 cm tall) and many small ornithischian dinosaur teeth from the Chinle have been referred to the type species, Revueltosaurus callenderi Hunt. A careful re-examination of the type and referred material of Revueltosaurus callenderi reveals that: (1) R. callenderi is a valid taxon, in spite of cladistic arguments to the contrary; (2) many teeth previously referred to R. callenderi, particularly from the Placerias quarry, instead represent other, more basal, ornithischians; and (3) teeth from the vicinity of St. Johns, Arizona, and Lamy, New Mexico previously referred to R. callenderi pertain to a new species, named Revueltosaurus hunti here. R. hunti is more derived than R. callenderi and is one of the most derived Triassic ornithischians. However, detailed biostratigraphy indicates that R. hunti is older (Adamanian: latest Carnian) than R. callenderi (Revueltian: early-mid Norian). Both taxa have great potential as index taxa of their respective faunachrons and support existing biochronologies based on other tetrapods, megafossil plants, palynostratigraphy, and lithostratigraphy.