Boring algae, fungi and bacteria have been the most constant factor in bioerosion through earth history. Their record reaches back into the middle Precambrian. The only fossil reefs specifically researched for these microendoliths are of Triassic and Upper Jurassic age. Boring worms appear in reefs in the Lower Cambrian. Boring sponges and bivalves first appear also in the lower Paleozoic, but do not become abundant in reefs until the Triassic. Effective substrate excavating grazers are relatively young geologically: Patellids and substrate excavating Echinoids evolved in the Triassic but did not become important bioeroders until the Jurassic or Cretaceous. Scarid fishes are even younger, the oldest representatives having been found in the Miocene. Thus, it seems that the intensity of bioerosion changed significantly during earth history. This may have had consequences for diversity of reef organisms, quality and quantity of reef debris, for diagenesis and record of reef rock.