Autofluorescence of microborings in fossil freshwater bivalve shells

Tubule system of earliest shells as a defense against increasing microbial attacks

“… 38 , 39 Dead shells, lacking biological defenses, are particularly susceptible to microbial attacks. 40 , 41 Cambrian shelly fossils often experienced extensive perforations by euendolithic cyanobacteria during postmortem burial and fossilization stages, 42 , 43 which made it difficult to distinguish microbial attacks on either living or dead shells. But given the fact that euendolithic microborers generally indiscriminately invade any abiotic and biotic carbonate substrates and formed microborings are distributed randomly within dead shells, the co-occurrence of some cyanobacterial microborings consistently surrounding the shell tubules in Nomgoliella confirms microbial attacks on living shells, and that the tubules themselves perform as obstacles or deterrents against boring microorganisms during the animal’s lifetime as believed.…”