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New in Journal of Systematic Palaeontology

Langer, M.C. and Benton, M.J. (2006). Early dinosaurs: a phylogenetic study. Journal of Systematic Palaeontology 4: 309?358.

SYNOPSIS: ?Early dinosaur evolution has been the subject of several phylogenetic studies and the position of certain basal forms is currently debated. This is the case for the oldest known members of the group, excavated from the Late Triassic Ischigualastian beds of South America, such as _Herrerasaurus_, _Eoraptor_, _Pisanosaurus_, _Saturnalia_ and _Staurikosaurus_. A new cladistic analysis of the early dinosaur radiation was performed to assess the relationships among the three major clades (Ornithischia, Sauropodomorpha and Theropoda) and to define the phylogenetic position of the basal members of the group. The most parsimonious hypothesis has _Silesaurus opolensis_ as the sister taxon to a dichotomy including monophyletic Saurischia and Ornithischia. The latter includes _Pisanosaurus mertii_, and the former all other well-known Triassic dinosaurs. Saurischia is composed of two major monophyletic groups: Herrerasauridae (including _Herrerasaurus ischigualastensis_ and _Staurikosaurus pricei_) and Eusaurischia (including the theropod and sauropodomorph lineages), while _Eoraptor lunensis_ appears to represent the sister taxon to Eusaurischia. _Saturnalia tupiniquim_ is a stem-taxon to Sauropodomorpha and _Guaibasaurus candelariensis_ might belong to the theropod branch. Some of these hypotheses are, however, not strongly supported. Especially uncertain are the affinities of _Silesaurus_ and _Guaibasaurus_. The latter can only be safely regarded as a saurischian, while the former might belong to the ornithischian lineage. The dinosaurian affinities of _Eoraptor_ and Herrerasauridae are strongly supported. Yet, the possibility that they (especially _Eoraptor_) represent basal theropods, rather than basal saurischians, cannot be dismissed. In fact, basal saurischian evolution is still too poorly understood for a definitive hypothesis of relationships to be presented."

Despite their own analysis, the authors seem very receptive to the idea that _Silesaurus_ might actually be an ornithischian, and therefore a true dinosaur. A recent article in Historical Biology pushes this idea a little more aggressively, based on a new Brazilian "silesaur". (I don't want to discuss the specifics, in case the HB article is not yet officially published.) If _Technosaurus_ (or part of the hypodigm) is a silesaur, it would mean that Triassic ornithischians were quite common and widespread. The jury is still out on this.

Averianov, A.O., Voronkevich, A.V., Leshchinskiy, S.V. and Fayngertz, A.V. (2006). A ceratopsian dinosaur Psittacosaurus sibiricus from the Early Cretaceous of West Siberia, Russia and its phylogenetic relationships. Journal of Systematic Palaeontology 4: 359?395.

SYNOPSIS: ?_Psittacosaurus sibiricus_ from the Aptian?Albian Ilek Formation at Shestakovo, Kemerovo Province, West Siberia, is represented by two almost complete adult skeletons, several associated groups of bones and numerous isolated bones of individuals ranging from post-hatchling to fully grown animals. _Psittacosaurus sibiricus_ differs from nine other species of the genus by a unique combination of 32 diagnostic characters, six of which are autapomorphies of the species: small infratemporal fenestra, anteroposteriorly short premaxilla, short medial process of postorbital, deep cleft for qaudratojugal on jugal, extending to the posterior side of jugal horn, angular with prominent tuber and 23 presacrals. _Psittacosaurus sibiricus_ is the sister species of _P. sinensis_, with which it shares the prominent pyramidal laterally projecting jugal horn, but more derived than the latter in having more developed palpebral and postorbital horns. The three lateral foramina on the exoccipital/ opisthotic are interpreted as exits for cranial nerves X+XI, XII1+2 and XII3, in contrast with previous interpretations. Cranial nerve IX exits the brain cavity through the metotic fissure. Most _Psittacosaurus_ localities are confined to lacustrine deposits and this animal undoubtedly inhabited areas around the great lakes widely distributed in Central Asia during the Early Cretaceous. The age of the _Psittacosaurus_ biochron is estimated as Hauterivian?Albian.?

The attribution for _P. sibiricus_ is given as: _Psittacosaurus sibiricus_ Voronkevich & Averianov in Leshchinskiy, Voronkevich, Maschenko, & Averianov, 2000.

Among other things, the authors also regard the SE Asian species _P. sattayaraki_ as valid.

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