SECULAR VARIATION IN THE DISTRIBUTION OF ENCRUSTING ORGANISMS THROUGH THE PHANEROZOIC
The number of sclerobiont reports increase from early- to middle- to late-epochs within periods of the Paleozoic (e.g. Early- to Middle- Devonian). Period boundaries correspond with decreases in the number of articles. Late Paleozoic encrusting communities are under-reported but common. There are no Permian and early Triassic sclerobiont communities reported in the peer-reviewed literature. The apparent lack of sclerobiont assemblages for this interval precedes the Permo/Triassic extinction and is more closely aligned with the formation of Pangea and the associated loss of shallow marine habitat. Reports of sclerobiont encrustation are more numerous in studies of Jurassic–Recent marine assemblages. A reported emergence (Zaton and Vinn, 2011) of a ‘modern’ encrusting community post-Middle Jurassic is consistent with our findings. Well-known sclerobiont occurrences may be epiboles. Work is needed to discern whether Permian and Triassic sclerobiont communities are truly rare or absent, or if their absence in the literature is an artifact.