REVISIÓN DE LOS BIOCOREMAS MARINOS GLOBALES DEL JURÁSICO SEGÚN LA DISTRIBUCIÓN DE LOS MOLUSCOS BIVALVOS

Abstract

Local and regional papers analyzing the distribution of Jurassic bivalves and proposing new palaeobiogeographic units of various ranks are numerous, but a worldwide synthesis was lacking. This paper is a review of those proposals with the aim to obtain a coherent synthesis of the global biogeo- graphic patterns from Early to Late Jurassic times, when significant changes in the Earth palaeogeography and oceanic circulation took place as the result of the breakup of Pangea. A brief account of the evolution in time and space of the recognized units and their relationships is also made. The biochoremas can be grouped into three first order units which had temporal continuity: Boreal, Tethys and Austral Realms. The units analysed here were recognized and characterized in very different grounds by their authors; the most commonly used criteria are degree of endemism, relative diversity and palaeobiogeographic affinities of bivalve genera. The patterns of Jurassic bivalve distribution are key to understand general biogeographic issues, but they were also used as evidence in palaeogeographic discussions (such as the establishment of seaways and changing patterns of superficial water circulation); they are even arguments in some palaeotectonic issues, such as the localiza- tion and history of displaced terranes, and continental drift.