Two separate species of tiny marine organisms, a sea-floor dweller and an ocean surface swimmer, are one and the same despite radical differences in lifestyle.
The surprising discovery suggests that the group survived the Cretaceous mass extinction by abandoning the poisonous oceans for a refuge in the relative safety of the sea-floor.
Foraminifers have lived throughout the oceans for many millions of years. They are microscopic, single-celled organisms with tiny shells and are so abundant in marine sediments that they have been used to trace long-term changes in the ocean's environment. Scientists have recognised two main groups: the benthics live in sea-floor sediments, while the planktics inhabit surface ocean waters as part of the plankton.
Dr Kate Darling, from the University of Edinburgh, and colleagues discovered that a planktic species living 600 nautical miles offshore in the Arabian Sea - the Streptochilus globigerus (pictured) - is genetically identical to a benthic species called Boliviana variabilis, found off the coast of Kenya.
'This was a very surprising discovery,' says Darling. 'It's the same biological species but it is living two separate lives: on the shallow continental shelf and as plankton at the surface of the open ocean.'
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Scientists think that all modern planktic foraminifers descend from a bottom-dwelling species that switched to a planktonic lifestyle sometime during the Mid to Early Jurassic, between 160 and 200 million years ago.
After the jump, the group diversified and new planktic species quickly colonised the oceans. Planktic foraminifers became very abundant, but only a small part survived the late Cretaceous extinction that killed off the dinosaurs. All modern planktic foraminifers are believed to descend from these lucky few.
Darling's findings complicate the story considerably. If some species can switch between free-swimming and bottom-dwelling lifestyles, then it's possible that 'most planktic foraminifers may have survived the KT [late Cretaceous] extinction in the sediment, not in the plankton,' says Darling.
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, argue the authors in the report published this week in the Proceedings of the National Academy of Sciences. When the oceans returned to normal, the survivors were able to recolonise the ocean surface once more.
Darling is still working on this idea, but it's very telling that 'two of the three types that survived the KT extinction belong to the same kind of foraminifera' she says, referring to the two species now revealed as one.
oh boy.
The implications are huge. Mama Nature may have just played a nasty prank on paleo types, especially the mass extinction folks. More as I have time.
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