Changes in ostracod provincialism during the Early Toarcian in the European epicontinental sea-Western Tethys area

Abstract

Spatial and temporal variations in ostracod biological diversity and composition are critical in understanding the role of paleoambiental on Pliensbachian-Toarcian mass extinction (Early Jurassic). An analysis based on a latest revision of the palaeobiogeographical distribution patterns of 274 Early Jurassic ostracods species within the Boreal and Tethyan provinces in the European-Western Tethys region suggests an important change in ostracod provincialism at the beginning of Toarcian. During the Early Jurassic, the ostracod faunas recovered from Western Europe show a change from a provincial to a cosmopolitan character. In the Late Pliensbachian, the ostracod assemblages from central and southern Europe changed from ostracod faunas characteristic of the Tethys Province to more cosmopolitan forms. This faunal change suggests that the temperatures of the water column changed from warm to temperate. From the late Pliensbachian and into the beginning of Toarcian new taxa, belonging to the Boreal Province (i.e. Ektyphocythere and Kinkelinella), appeared and established important evolutionary lineages on the South European platforms. The �cytheroid� spread matches to the extinction of the Superfamily Healdioidea in both provinces at the beginning of Toarcian. The change of fauna from provincial to cosmopolitan is connected with sea level variations, water temperature changes or ocean current patterns alterations.