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Tyrannosaurid Interrelationships paper

Sereno, P. C., and S. L. Brusatte. 2009. Comparative Assessment of
Tyrannosaurid Interrelationships. Journal of Systematic Palaeontology

Absract - We employ a new comparative method to four cladistic analyses of
tyrannosaurid dinosaurs to identify root causes for differences between
phylogenetic results. The comparative method is a three-step procedure that
(1) adjusts competing hypotheses so they share equivalent taxonomic scope,
(2) isolates the character data relevant to the common problem, and (3)
divides relevant character data into shared and novel partitions. It is
then possible to quantify the degree of similarity between character data
using three indices (ancestor similarity index, character similarity index
and character state similarity index).

The most parsimonious cladograms generated by the four analyses of
tyrannosaurids appear fairly congruent, with two subclades present in all
four analyses (Albertosaurus and Gorgosaurus versus Daspletosaurus,
Tarbosaurus and Tyrannosaurus). A comparative examination of the underlying
character data, however, highlights striking differences in character
selection and significant differences in character state scores. Character
selection and differences in scoring are root causes for phylogenetic
incongruence. Comparative analysis reveals the existence of many data-level
differences that remain largely obscured when comparison is limited to the
most parsimonious cladograms.

Bill Parker
Vertebrate Paleontologist
Division of Resource Management
Petrified Forest National Park
P.O. Box 2217
1 Park Road
Petrified Forest, AZ 86028
(928) 524-6228 x262