Enigmatic microfossils from southern Poland

Spirotubus are puzzling microfossils from southern Poland, dating from the Devonian period, around 380 million years ago. The Spirotubus skeletons are tiny calcareous (calcitic) tubes with a spiral pattern on their outer surface. The organisms that built these skeletons lived in shallow, isolated marine lagoons, where the water was highly saturated with calcium carbonate, which likely facilitated the formation of their massive skeleton. We do not know what kind of organisms formed these fossils: Spirotubus does not resemble any known modern or fossil species.

Illustration: Various microstructures of Spirotubus carbonate skeletons under a scanning microscope.