Pre-Cenozoic Fossil Record of Cryptobionts and Their Presence in Early Reefs and Mounds

The fossil record of cryptobionts (cryptic organisms) in various kinds of hard substrates spans the Phanerozoic, with the oldest known atpresentfrom Ordovician and early Cambrian reefs and reef mounds. The earliest cryptobiontic assemblagesupport views that there probably was only very weak polarization of surface-exposed and cryptic communities inthe early Paleozoic; by the middle Paleozoic polarization seems to have increased, but did not reach levels comparable to that seen in modern reefs until at least the Mesozoic. There are few accounts of cryptobionts in Cambrian and Ordovician reefs and reef mounds, but some generalizations can be made: 1) early Paleozoic cryptic communities were of low to moderate diversity by the standards of the time; 2) cryptobiontic assemblages generally reflected the makeup of the reef surface assemblages, but there appear to be differences in the importance of some groups within cavities compared to outside; 3) the earliest cryptobionts were micro-organisms or very small metazoa; larger cryptobionts areeither uncommon, or are dubious cryptobionts.