Phyletic Relationships of Living Sharks and Rays

A set of hypotheses are developed for the origin of living sharks and rays and the interrelationships of their major groups, using some methods of cladistic analysis to relate groups with shared derived characters. Comparative studies on living sharks and rays combined with new data on fossil sharks suggests that the living groups ultimately stem from a common ancestral group of “neoselachian” sharks with many modern characters. Reinterpretations of “amphistyly” in modern sharks is presented on new data.