The concept of the three great evolutionary faunas of marine animals from the Cambrian to the present (that is, the entire Phanerozoic) was introduced by Jack Sepkoski in 1981 using factor analysis of the fossil record.
This fauna comprises trilobites, small shelly fossils (grouped by Sepkoski into "Polychaeta", but including cribricyathids, coleolids, and volborthellids), Monoplacophora, inarticulate brachiopods and hyoliths.
[3] This fauna is marked by fossils of the following classes: Articulata, Crinoidea, Ostracoda, Cephalopoda, Anthozoa, Stenolaemata, Stelleroidea.
Fauna III, known as "Modern", described as a "Mollusc-rich assemblage", arose largely in the Mesozoic-Cenozoic Radiation, still in progress.
The following classes are included: Gastropoda, Bivalvia, Osteichthyes, Malacostraca, Echinoidea, Gymnolaemata, Demospongiae, Chondrichthyes.