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There is little consensus on the systematic position of the colossal theropod dinosaur
Chilantaisaurus tashuikouensis from the Cretaceous (Aptian–?Albian or Upper Cretaceous)Ulansuhai Formation of Inner Mongolia, which has been recovered as a derived member of both Allosauroidea and Spinosauroidea by numerical phylogenetic analyses. Redescription of the type material of C. tashuikouensis reveals an unusual combination of morphological features that render determination of its systematic position problematic. It possesses anatomical features that have been proposed as synapomorphies of Neotetanurae: a preacetabular fossa on the ilium, and a wedge-shaped crosssection of the shaft of the thi ... Read more »
Viewings: 6209 | Data: 16.09.2008 | Rating: 4.2/13 | Comments (6)

Cope’s rule, the tendency towards evolutionary increases in body size, is a long-standing macroevolutionary generalization that has the potential to provide insights into directionality in evolution; however, both the definition and identification of Cope’s rule are controversial and problematic. A recent study [J. Evol. Biol. 21 (2008) 618] examined body size evolution in Mesozoic birds, and claimed to have identified evidence of Cope’s rule occurring as a
result of among-lineage species sorting. We here reassess the results of this study, and additionally carry out novel analyses testing for within-lineage patterns in body size evolution in Mesozoic birds. We demonstrate that the nonphy ... Read more »
Viewings: 4089 | Data: 15.09.2008 | Rating: 4.5/2 | Comments (0)

The rise and diversification of the dinosaurs in the Late Triassic, from 230 to 200 million
years ago, is a classic example of an evolutionary radiation with supposed competitive
replacement. A comparison of evolutionary rates and morphological disparity of basal dinosaurs and their chief “competitors,” the crurotarsan archosaurs, shows that dinosaurs exhibited lower disparity and an indistinguishable rate of character evolution. The radiation of Triassic archosaurs as a whole is characterized by declining evolutionary rates and increasing disparity, suggesting a decoupling of character evolution from body plan variety. The results strongly suggest that historical contingency, rather t ... Read more »
Viewings: 4874 | Data: 15.09.2008 | Rating: 4.7/3 | Comments (0)

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