Richard Butler's full description of the early ornithischian Eocursor parvus is now available online in the Zoological Journal of the Linnaean Society. As detailed by Richard, this taxon is of importance not only because of its phylogenetic position, but also because it represents only one of three purported ornithischian specimens from the Triassic Period and is the best preserved.
Unlike Pisanosaurus and the unnamed jaw fragment from Argentina assigned to the Heterodontosauridae, Eocursor can clearly be demonstrated to be a bona fide ornithischian. The potential problem with this specimen, and outlined in the paper, is debate on the stratigraphic position and thus the age of the specimen. There is indeed the possibility that this specimen may actually be Jurassic in age and hopefully some future studies on the provenance and age of the specimen can be done to verify the age. Splitting hairs? Maybe, but the exact age is very important when looking at tempo and mode of early dinosaur evolution. When you only have three physical specimens of a group from a specific time period, each one is of the utmost importance.
Nonetheless, this is still an extremely important specimen and congratulations to Richard on another solid contribution to vertebrate paleontology and early dinosaur studies.
Butler, R. J. 2009. The anatomy of the basal ornithischian dinosaur Eocursor parvus from the lower Elliot Formation(Late Triassic) of South Africa. Zoological Journal of the Linnaean Society. Published early online, doi: 10.1111/j.1096-3642.2009.00631.x
Abstract - Ornithischia is a morphologically and taxonomically diverse clade of dinosaurs that originated during the Late Triassic and were the dominant large-bodied herbivores in many Cretaceous ecosystems. The early evolution of ornithischian dinosaurs is poorly understood, as a result in part of a paucity of fossil specimens, particularly during the Triassic. The most complete Triassic ornithischian dinosaur yet discovered is Eocursor parvus from the lower Elliot Formation (Late Triassic: Norian–Rhaetian) of Free State, South Africa, represented by a partial skull and relatively complete postcranial skeleton. Here, the anatomy of Eocursor is described in detail for the first time, and detailed comparisons are provided to other basal ornithischian taxa. Eocursor is a small-bodied taxon (approximately 1 m in length) that possesses a plesiomorphic dentition consisting of unworn leaf-shaped crowns, a proportionally large manus with similarities to heterodontosaurids, a pelvis that contains an intriguing mix of plesiomorphic and derived character states, and elongate distal hindlimbs suggesting well-developed cursorial ability. The ontogenetic status of the holotype material is uncertain. Eocursor may represent the sister taxon to Genasauria, the clade that includes most of ornithischian diversity, although this phylogenetic position is partially dependent upon the uncertain phylogenetic position of the enigmatic and controversial clade Heterodontosauridae.
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