ABSTRACT
On the basis of the spatial distribution of the Silurian endemic brachiopods from South America and Africa, the replacement of the name ‘Silurian Malvinokaffric Realm’ and ‘Clarkeia Fauna’, by the name Afro-South American Realm is proposed. From current evidence, the last members of this realm extend to the earliest Devonian (Early Lochkov/Gedinne). This realm is characterised by the widespread distribution of Heterorthella and other endemic genera, the absence of Pentameroidea, and paucity of Spiriferoidea. Endemism within the Afro-South American Realm shows gradual increase from the Llandovery to Ludlow-Pridoli. Neither geographic distribution nor taxonomic composition of the Afro-South American Realm brachiopods is uniform throughout the Silurian. During the Llandovery, two areas can be differentiated, (1) an infracratonic area characterised by endemics-dominated assemblages, and, (2) an epicratonic Andean area, typified by very low endemism, and presence of several North Silurian Realm taxa. As a result of faunal turnover at the end of the Llandovery, brachiopod faunas were strongly depleted. During the Wenlock-Early Ludlow transgressive event, the open platform was colonised by low-diversity communities dominated by Harringtonina and Australina. By the Ludlow-Pridoli, high-diversity communities including endemic taxa and new immigrants, such as Salopina, Isorthis and Coelospira, flourished in nearshore, well-oxygenated muddy deposits. The end of the Early Lochkov is punctuated by extinction of the last Afro-South American endemics, and the appearance of quite different brachiopod assemblages characteristic of the Devonian ‘Malvinokaffric Realm’. Diversity and distribution of brachiopod faunas were controlled primarily by ecologic factors. However, influx of North Atlantic taxa into the Afro-South American Realm in the Silurian and earliest Devonian seems to have been related to relative position of the basins with respect to the continent. Immigrant taxa increased towards the continental margin, especially in the Precordilleran foreland basin.
