TURNOVER RATES OF PALEOZOIC AND MODERN TAXA DURING THE LATE PALEOZOIC ICE AGE

The Late Paleozoic Ice Age (LPIA) was a phase of major climatic changes in Earth’s history and serves as an analogue to today’s conditions of globally increasing ocean temperatures, continuously melting ice caps, and rising sea-levels. Better understanding of the effects of the LPIA on macroevolutionary patterns can help in predicting the consequences of these impacts on the flora, fauna, and human life. Therefore, we focus on the changes regarding turnover rates and diversity of marine, benthic taxa during the LPIA. Using occurrence data from the Paleobiology Database (PBDB), we have compared the Paleozoic (here: brachiopods) with the modern evolutionary fauna (here: bivalves, gastropods) and investigated the roles of environmental factors in determining their diversity dynamics.

During the early phase of the ice age, taxa show similar trends of diversity. However, brachiopods demonstrated a pronounced diversification during the Permian, which is less distinct for bivalves and gastropods. Origination rates of all taxa are elevated in the earliest Carboniferous, while extinction rates are especially high in the Viséan and particularly from the Wordian onward. Towards the end-Permian mass extinction, brachiopods had markedly higher turnover rates than bivalves and gastropods. Yet, rates of all taxa are similar throughout the main phase of the LPIA, suggesting that in this interval, clade membership was a less important determinant of temporal turnover than environmental conditions.

Siliciclastics and carbonates are similarly preferred, but more taxa show affinities towards shallow marine and non-reefal settings during the LPIA. The separate investigation of the gastropods, bivalves, and brachiopods revealed that grain size is less important. Bivalves had an affinity towards siliciclastic, shallow marine, non-reefal environments. The latter preferences also apply for gastropods and brachiopods except that they have a slight affinity towards carbonates. Focusing on turnover rates in individual environments (all three taxa combined), results are similar; i.e., rates were higher at the beginning of the LPIA representing the recovery after the Frasnian-Famennian mass extinction, and rates are low during the LPIA, indicating the adaption of taxa to more variable climatic and environmental conditions.