The stratigraphic record of microborings

Approximately 50 fossil endolith species (biotaxa and ichnotaxa) were screened for their stratigraphic ranges. The study indicates (i) the first occurrence of microborings in the Proterozoic and of some others in the Ordovician and Silurian, (ii) diversity increases at the base of the Mesozoic, (iii) and a change in taxa composition at the base of the Cenozoic. Remarkably, 35% of the endolith taxa are known from the Proterozoic or Palaeozoic until now and can be considered as "living fossils". The protected microenvironment in omnipresent calcareous substrates, the speed of endolith spore settlement, and the ability of photoautotrophic endoliths to tolerate declining light levels are regarded as important reasons for their longevity. The first borings were made by Cyanobacteria in the Proterozoic, whereas the endolithic niche became established by Chlorophyta by the Ordovician, by Rhodophyta by the Silurian (perhaps already the Ordovician), and by fungi by the Ordovician