Key to surviving mass extinction? Lead a double life

Single-cell marine creatures might have survived the Earth’s last mass extinction event by leading a sort-of double life, according new research.

A team of experts, including scientists from the University of Nottingham, have found evidence that planktonic foraminifera — single-celled shell building members of the marine microplankton community– might have survived the end-Cretaceous mass extinction 65 million years ago by taking refuge on the sea floor.

Scientists previously thought that all modern planktic foraminifers were descended from the few lucky survivors of the meteor impact that wiped out the dinosaurs — as well as 65 to 70 per cent of all life on Earth — 65 million years ago. However, this might not be the case.

Researcher Chris Wade from the Institute of Genetics, together with PhD student Heidi Seears, have shown that live specimens of the planktonic species Streptochilus globigerus, collected 600 miles offshore in the middle of the Arabian Sea, are genetically identical to the benthic species Bolivina variabilis, found off the coast of Kenya.

Their surprising discovery suggests that planktonic foraminifera may have survived the end-Cretaceous mass-extinction by abandoning the poisonous oceans for a refuge in the relative safety of the sea-floor. When the oceans returned to normal, the survivors were able to recolonise the ocean surface once more.

“Using genetic data we have been able to prove that the planktonic species Streptochilus globigerus and the benthic — sediment-living — foraminiferan Bolivina variabilis are one and the same biological species,” said Chris Wade from the Institute of Genetics. “Moreover, geochemical evidence shows that this species actively grows within the open-ocean surface waters, thus occupying both planktonic and benthic domains. Such ecologically-flexible species are eminently suited to the recolonisation of the extinction-susceptible planktonic domain following mass extinctions events, such as the end-Cretaceous event.”

The research, carried out in collaboration with the University of Edinburgh, has been published in the journal Proceedings of the National Academy of Sciences (PNAS).

“If some species can switch between free-swimming and bottom-dwelling lifestyles, then it’s possible that most planktic foraminifers may have survived the late Cretaceous extinction in the sediment, not in the plankton,” said Kate Darling, from the University of Edinburgh. “It seems likely that the foraminifer species which had the ability to occupy both habitats survived on the sea-floor, avoiding the meteor impact catastrophe in the oceans above.”