Published online by Cambridge University Press: 26 July 2017
Marine metazoans have lived infaunally throughout the Phanerozoic. The biotic history of the infaunal habitat is, however, poorly understood. Only the two extremes are relatively well known; the Precambrian had a limited infaunal biological benthic boundary layer (the depth below the sediment-water interface that is occupied or otherwise influenced by benthic organisms [Rhoads and Boyer, 1982]), whereas modern environments have a well-developed infaunal biological benthic boundary layer with extensive and deep bioturbation.