COMMENTS ON WESTERN HEMISPHERE JURASSIC FISHES

Abstract

Subgroups of modern sharks, chimaeroids, chondrosteans and teleosts first occur in the fossil record during the Jurassic Period. The Jurassic fishes of England, France and Germany are the most diversified and thoroughly studied and are therefore of primary importance in the identification and description of Jurassic fishes from other parts of the world. Important Jurassic fish assemblages have recently been described from the United States .and from Argentina and Chile, Detailed consideration of the American taxa has indicated to us that a distinction must be made between wide-ranging, paraphyletic form taxa such as Ceratoilus and unique, monophyletic taxa that have no recognizable relatives. Neither of these categories will provide valid information 'for faunal comparisons, and their inclusion will lead to false conclusions about historical biogeography and stratigraphic correlation