Metal-induced malformations in early Palaeozoic plankton are harbingers of mass extinction

Abstract

Glacial episodes have been linked to Ordovician–Silurian extinction events, but cooling itself may not be solely responsible for these extinctions. Teratological (malformed) assemblages of fossil plankton that correlate precisely with the extinction events can help identify alternate drivers of extinction. Here we show that metal poisoning may have caused these aberrant morphologies during a late Silurian (Pridoli) event. Malformations coincide with a dramatic increase of metals (Fe, Mo, Pb, Mn and As) in the fossils and their host rocks. Metallic toxins are known to cause a teratological response in modern organisms, which is now routinely used as a proxy to assess oceanic metal contamination. Similarly, our study identifies metal-induced teratology as a deep-time, palaeobiological monitor of palaeo-ocean chemistry. The redox-sensitive character of enriched metals supports emerging ‘oceanic anoxic event' models. Our data suggest that spreading anoxia and redox cycling of harmful metals was a contributing kill mechanism during these devastating Ordovician–Silurian palaeobiological events.

From success to persistence: Identifying an evolutionary regime shift in the diverse Paleozoic aquatic arthropod group Eurypterida, driven by the Devonian biotic crisis

“…The Silurian is characterized by multiple pulses of ocean anoxia and heavy metal excursions (Vandenbrouke et al. ), resulting in an unstable environment with a high degree of biotic turnover. This boom and bust macroevolution can maintain high standing diversity while the system is maintained; however, a reduction in rates can impact groups differently depending on whether they were in a boom or bust phase.…”

A record of Late Ordovician to Silurian oceanographic events on the margin of Baltica based on new carbon isotope data, elemental geochemistry, and biostratigraphy from two boreholes in central Poland

“…It is possible that these signals may also be linked with the occurrence of malformed phytoplankton during early Paleozoic bioevents reported in some studies (Munnecke et al, 2012). These authors have suggested that high levels of dissolved heavy metals in the water column, including Fe 2 O 3 and Pb, may be linked to the teratological assemblages (Vandenbroucke et al, 2015). This is thought to have been driven by persistent anoxia in the deep sea and remobilization of redox sensitive elements (Emsbo et al, 2010;McLaughlin et al, 2012a).…”

“…The cause of these positive "excursions" in the Silurian is a matter of some debate (Saltzman, 2003;Cramer and Saltzman, 2007a;Loydell, 2007Loydell, , 2008Cramer and Munnecke, 2008;McLaughlin et al, 2012a;Vandenbroucke et al, 2015), nevertheless, it is generally thought that these phenomena are linked to widespread burial of isotopically light organic carbon ( 12 C) in the deep sea, leaving the atmosphere and hydrosphere preferentially enriched in heavy 13 C (Kump and Arthur, 1999;Saltzman and Thomas, 2012). These appear to be global phenomena.…”

Mesozoic climates and oceans – a tribute to Hugh Jenkyns and Helmut Weissert

“…There are many examples of black shale deposition associated with geochemical anomalies for both the Early Palaeozoic (e.g. McLaughlin et al ., ; Vandenbroucke et al ., ) and the Late Palaeozoic (e.g. Carmichael et al ., , ; De Vleeschouwer et al ., ); as more data are acquired from a range of depositional settings, so the global nature of these events and their similarities to Mesozoic counterparts are becoming more clearly established.…”