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.
Highlights
Glacial episodes have been linked to Ordovician–Silurian extinction events, but cooling itself may not be solely responsible for these extinctions
Whereas modern instances of teratology in aquatic micro- and macroorganisms have been linked to a variety of environmental stressors, the teratological effects of heavy metal pollution have been well established in the natural environment and laboratory a c b experiments
We show that their teratology coincides with metal enrichment in host rocks and fossils
Summary
Glacial episodes have been linked to Ordovician–Silurian extinction events, but cooling itself may not be solely responsible for these extinctions. In terms of affected functional morphology, these modern case studies involving cysts and eggs are strikingly similar to those of chitinozoans and acritarchs in the early Palaeozoic record. In the modern, such studies of resting stages are uncommon because the producing organism can be studied directly. Chitinozoans are organic-walled microfossils (palynomorphs), 100–500 mm long, which probably represent fossil egg cases of marine zooplankton that lived in the shallow mixed layer of the Ordovician–Silurian oceans[27]. We show that their teratology coincides with metal enrichment in host rocks and fossils
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