Looking for the oldest diatoms

Paleontological observations of ancient flora and fauna provide powerful insights into past diversity and relationship
dynamics between organisms and their environments. Diatoms are globally distributed protists that
influence major biogeochemical cycles and sustain oceanic food webs. The fossil diatom record extends 120
million years back to the Early Cretaceous where rare deposits were discovered worldwide and are occasionally
represented by diverse communities. However scarce, the taxonomic richness and geographical spread of these
diatom communities suggest prior evolutionary events and therefore earlier deposits. To complement the existing
fossil information and to discover diatom deposits predating 120 Ma, we examined 33 study sites from cores and
outcrops across oceans and continents. These efforts did not generate new fossil discoveries, however. Our
assessment suggests biogenic silica that comprises the cell wall of diatoms was likely dissolved from Mesozoic
sediments through diagenetic processes. Altogether, the search for the oldest diatoms must continue but should
target sediments that experienced shallow burial and concretions.