RECOGNIZED GLOBALLY, MANIFESTED LOCALLY: SEPKOSKI’S EVOLUTIONARY FAUNAS IN NORTH AMERICAN CAMBRIAN-ORDOVICIAN BENTHIC ASSEMBLAGES
The transition between the Cambrian and Paleozoic faunas appears to occur gradually during the Ordovician. Lower Ordovician assemblages contain approximately equal proportions of Cm and Pz faunal elements in the target environment. In agreement with previous work, these assemblage data support a broad onshore-offshore differentiation of community types in the Ordovician. Shallow-water, nearshore environments exhibit a higher proportion of Modern faunal elements than do deep subtidal assemblages. Corroboration of an onshore-offshore distinction in faunal composition, combined with a strong correlation of evolutionary faunal proportions between deep subtidal assemblages and Sepkoskis global compilation, suggests that the deep subtidal zone may contain the majority of known Cambrian and Ordovician genera. Alternatively, Sepkoskis data may preferentially represent this depth zone in North America. Regardless of the reason for the good correspondence, relative genus richness of the evolutionary faunas in Sepkoskis global compilation is a good predictor of the composition of deep subtidal assemblages in the Cambrian and Ordovician of North America.