Biogeography of Ordovician, Silurian, and Devonian Chitinozoans

hirteen paleobiogeographic charts are presented for Ordovician, Silurian, and Devonian chitinozoans. The compilation of these has been difficult for several reasons: little is known of the chitinozoans from some geographic regions; stratigraphic information about the occurrence of these microfossils is often imprecise; and there is little uniformity in chitinozoan taxonomy. Paleobiogeographic interpretations must also take into consideration the paleoecology of chitinozoans, since some of these animals had a planktonic, others a benthic mode of life. All chitinozoans were bathymetrically controlled but as shown in a graph of abundance, the benthic forms were more common than the planktonic. Despite the possible sources of error, it is evident that chitinozoa display some provincialism. Ordovician chitinozoans are conspicuously provincial. Silurian chitinozoa are predominantly cosmopolitan. Devonian taxa are halfway between these extremes.