Introduction

Abstract

Bivalves have proven to have a great potential for paleobiogeographic analyses due to their relatively complete fossil record, especially for Mesozoic and Cenozoic times. Being mostly benthonic, they have a large variety of life habits which should be taken into account, particularly in detailed paleobiogeographic studies. We will analyze marine bivalve distribution in the Southern Hemisphere during several successive time slices within the Triassic and Jurassic, an epoch marked by critical geologic and biotic events. This period covers both the biotic recovery after the harshest diversity crisis ever (the Permian/Triassic extinction event), and later also the biotic reaction to another severe crisis at the Triassic/Jurassic boundary. This allows the opportunity to evaluate the response of paleobiogeographic patterns to such events. The Earth’s configuration drastically changed from a concentration of land masses in a unique supercontinent (Pangea) and two oceans (Tethys and Panthalassa), to a fragmented series of continental land masses. These began to disperse, opening sea corridors which largely affected not only the global distribution of biotas but also paleoclimate and sea paleocurrents as well. This dynamic paleogeography adds an interesting ingredient to the study of past distributions of benthic organisms making it possible to frame them into a physically and biologically changing scenario.

‘Every naturalist who has directed his attention to the subject of the geographical distribution of animals and plants, must have been interested in the singular facts which it presents… Of late years, … a great light has been thrown upon the subject by geological investigations, which have shown that the present state of the earth, and the organisms now inhabiting it, are but the last stage of a long and uninterrupted series of changes which it has undergone, and consequently, that to endeavour to explain and account for its present condition without any reference to those changes (as has frequently been done) must lead to very imperfect and erroneous conclusions.’

Alfred Russel Wallace 1855