SECULAR VARIATION IN THE DISTRIBUTION OF ENCRUSTING ORGANISMS THROUGH THE PHANEROZOIC

Fossil encrusting organisms exhibited temporal and paleogeographic patterns that can be broadly correlated with identifiable environmental conditions. A preliminary literature survey of 50 studies that span the Phanerozoic shows encrustation occurs preferentially within a paleolatitudinal zone of approximately 30 ^ͦ S to 30 ^ͦ N. Modern encrusting communities have been reported outside this latitudinal range, but exceptions are geographically isolated. Fossil encrusters also show a correlation between increased available marine substrate and number of documented sclerobiont communities, probably reflecting global eustatic conditions and/or tectonic configuration.

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.