A new look at archaeocyaths

An alternative explanation of the systematic position of archaeocyaths, Cambrian calcareous fossils interpreted for over 30 years mostly as sponges (Porifera), herein treated as closely related to modern siphonous green algae, especially representatives of the genus Codium (Bryopsidales, Chlorophyta). The basis for this conclusion was the demonstration, grounded on samples from NE Siberia, that the skeleton of archaeocyaths was not an indigenous product of the siphonous algae, but the product of calcified microorganisms, close to modern cyanobacteria (Chroococcales), that overgrew the algae during their lifetime. The calcification of cyanobacterial epibiontic biofilms on siphonous green algae thalli evidences high saturation of the Cambrian sea with calcium carbonate (“calcium stress”), which should be considered one of the main causes of the mass formation of first calcareous skeletons at that time. This is an aspect of the Cambrian explosion, one of the major events in the history of life.

NCN 2015/17 / B / ST10 / 03340, leader prof. dr. hab. Józef Kaźmierczak.