New in Journal of Systematic Palaeontology

[Tim Williams <twilliams_alpha@hotmail.com>]

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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