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Something else complete different: Triassic Crurotarsi vs Ornithodira in latest Science

Brusatte, S.L., M.J. Benton, M. Ruta, G.T. Lloyd. 2008. Superiority,
Competition, and Opportunism in the Evolutionary Radiation of Dinosaurs.
Science 321:1485-1488.

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 than prolonged competition or general
"superiority," was the primary factor in the rise of dinosaurs.

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
Fax: 301-314-9661               

Faculty Director, Earth, Life & Time Program, College Park Scholars
Fax: 301-405-0796

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA