Phyletic Relationships of Living Sharks and Rays

A set of hypotheses are developed for the origin of living sharksand rays and the interrelationships of their major groups, usingsome methods of cladistic analysis to relate groups with sharedderived characters. Comparative studies on living sharks andrays combined with new data on fossil sharks suggests that theliving groups ultimately stem from a common ancestral groupof "neoselachian" sharks with many modern characters. Reinterpretationsof "amphistyly" in modern sharks is presented on new data.