F. Robin O'Keefe

Academic paper

Journal of Vertebrate Paleontology

Abstracts

21

3

Recent work on the phytogeny of the Plesiosauria (Reptilia: Sauropterygia) has demonstrated that the "pliosauromorph" body type evolved three times within the clade. The pliosauro-morph body type is characterized by a large head, a short neck, and proportions of the limbs and limb girdles. A morphometric study has further demonstrated that evolution of the pliosauromorph body type followed different paths through morphospace. The present study uses compatibility ordination and partition analysis to investigate how correlated morphological characters influence estimates of phylogeny. Compatibility ordination demonstrates that morphometric characters do in fact cluster on compatibility axes, supporting the hypothesis that these characters are dependent. Weighting of morphometric characters improves the resolution and stability of the resulting cladogram. Monte Carlo-based partition analysis is used to test the data set for dependent character sets. Thirteen significant character partitions are identified, and the partitions are devisable into three broad categories. The first set of partitions is attributable to functional correlation; morphometric characters known to be dependent based on morphometric analysis and compatibility ordination are prominent in these partitions, and are joined bv other characters with clear functional implications. The second group of character partitions diagnose major taxonomic groups in the plesiosaur cladogram. These

English