The new paper by Max Langer and collaborators (Langer et al., 2009) provides a phylogenetic definition for the clade Silesauridae. Silesaurids are gracile, quadrupedal, hebivorous/omnivorous dinosauriforms whose first announcement in 2003 (Dzik, 2003) generated a large amount of interest in early dinosaur phylogeny. In fact there were at least five presentations at this years SVP meeting alone that dealt with silesaurs.
Langer et al. (2009) define Silesauridae as "all archosaurs closer to Silesaurus opolensis, than to Heterodontosaurus tucki and Marasuchus lilloensis". Currently it is pretty much agreed that Silesauridae contains Silesaurus opolensis, Sacisaurus agudoensis, Eucoelophysis baldwini, and Pseudolagosuchus major (Nesbitt et al., 2005; Ezcurra, 2006; Irmis et al., 2007b; Langer et al., 2009). Silesaurus also possibly contains Lewisuchus admixtus, Technosaurus smalli, and an isolated specimen from Petrified Forest National Park (Irmis et al., 2005; Parker et al., 2006; Nesbitt et al., 2007; Langer et al., 2009).
Since their first publication it has been debated whether this clade represent dinosauriforms (e.g., Parker et al., 2006; Irmis et al., 2007a; Nesbitt et al., 2007) or possibly basal ornithischians (e.g., Ferigolo and Langer, 2007; Dzik and Sulej, 2007). Currently there is much more support for placement as the sister taxon of Dinosauria (Ezcurra, 2006; Irmis et al. 2007b, Langer et al., 2009). Nonetheless, silesaurids most likely filled an ecological niche later filled by ornithischian and thus possibly supressed early ornithischian diversity through the Late Triassic.
Dzik, J. 2003. A beaked herbivorous archosaur with dinosaur affinities from the early Late Triassic of Poland. Journal of Vertebrate Paleontology 23:556-574.
Dzik, J., and T. Sulej. 2007. A review of the Early Triassic Krasiejow biota from Silesia, Poland. Paleontologia Polonica 64:3-27.
Ezcurra, M. D. 2006. A review of the systematic position of the dinosauriform archosaur Eucoelophysis baldwini from the Upper Triassic of New Mexico, U.S.A. Geodiversitas 28:649-684.
Ferigolo, J. and M. Langer. 2007. A late Triassic dinosauriform from south Brazil and the origin of the ornithischian predentary bone. Historical Biology 19:23-33.
Irmis, R. B., Parker, W. G., and S. N. Nesbitt, 2005. Critical review of the Late Triassic dinosaur record, part 2: Ornithischia. Society of Vertebrate Paleontology 25(3):73A.
Irmis, R. B., Parker, W. G., Nesbitt, S. J., and J. Liu, 2007. Early ornithischian dinosaurs: the Triassic Record. Historical Biology 19:3-22.
Irmis, R. B., Nesbitt, S. J., Padian, K., Smith, N. D., Turner, A. H., Woody, D., and A. Downs. 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317:358-361.
Nesbitt, S. N., Irmis, R. B., and W. G. Parker, 2005. Critical review of the Late Triassic dinosaur record, part 3: Saurischians of North America. Society of Vertebrate Paleontology 25(3):96A.
Nesbitt, S. J., Irmis, R. B., and W. G. Parker. 2007. A critical reevaluation of the Late Triassic dinosaur taxa of North America. Journal of Systematic Palaeontology 5:209-243.
Parker, W. G., Irmis, R. B., and S. J. Nesbitt. 2006. Review of the Late Triassic dinosaur record from Petrified Forest National Park, Arizona. Museum of Northern Arizona Bulletin 62:160-161.
What if we done the Schrodinger's cat experiment?
12 hours ago in Doc Madhattan