BRACHIOPOD HIERARCHICAL DIVERSITY PARTITIONING IN THE LATE ORDOVICIAN?EARLY SILURIAN: RECOVERY PATTERNS AFTER THE LATE ORDOVICIAN EXTINCTION

HALPERN, K.; BALSEIRO, D.

Congreso; 4th International Palaeontological Congress; 2014

p { margin-bottom: 0.25cm; line-height: 120%; } Brachiopod global diversity trend shows a negative excursion in the Ordovician-Silurian boundary. This sharp decrease in diversity, interpreted as the Late Ordovician Extinction, can also be recognized at regional scales when drawing diversity curves with raw data. Recent studies demonstrate the existence of important geographic variability in diversity trends during this interval. However, diversity patterns analyzed so far represent equatorial and subequatorial paleoplates, while diversity trends in high-latitudes are virtually unknown. We here analyze brachiopod standardized diversity trends in a hierarchical scheme (alpha, beta and gamma) from Late Ordovician to Early Silurian among 4 regions, namely Laurentia, Baltica, Avalonia and the Argentine Precordillera. Gamma diversity shows similar trends in Avalonia and Baltica, increasing from Lower Caradocian to the Ashgillian, diminishing towards the Rhuddanian and, after a slight increase in the Aeronian, dropping in the Telychian. In the Argentine Precordillera gamma diversity progressively decreases from the Upper Caradocian to the Rhuddanian. Meanwhile, in Laurentia gamma diversity trend records a continuous rise from Lower Caradocian through the Telychian. Alpha diversity, however, shows a different trend across the Ordovician-Silurian boundary. In all regions but Baltica, alpha diversity diminishes from the Upper Caradocian to the Ashgillian but then stays stable across the Ordovician-Silurian boundary until the Aeronian. Instead, Baltica shows a peak of alpha diversity in the Ashgillian, a slight decrease in the Rhuddanian and drops in the Aeronian. As it could be expected, beta diversity also shows geographic variation. The general pattern is that beta diversity decreases by 50% from the Ashgillian to the Rhuddanian, being the largest drop in beta diversity recorded at the Ordovician-Silurian boundary. On the contrary, Laurentia?s beta diversity increases steadily from the Lower Caradoc to the Telychian. These diversity patterns suggest geographic variability in recovery dynamics, having migration and speciation different importance in each region. On the one hand, local communities in Baltica, Avalonia and Precordillera seem to have recovered their diversity based on migration, provoking a homogenization of the faunas and a subsequent beta diversity loss. On the other hand, local communities in Laurentia, most probably recovered their diversity based on higher speciation, and hence beta diversity increased. Moreover, our results also indicate a mismatch in the recovery at different geographic scales. While local communities recover quickly, at regional scale metacommunities can have a much protracted recovery interval.