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Carboniferous-Permian Biogeography |
Department of Geology, West Georgia College, Carrollton, GA 30118 USA
The 100 blastoid genera are known from some 1500 localities on every continent except Antarctica. Although fissiculates were more geographically widespread than spiraculates, the spiraculates tended to dominate most faunas numerically. The typical blastoid genus is monospecific, relatively short lived (range limited to some part of a single stage), relatively rare in terms of abundance, and geographically restricted to one depositional basin. Throughout their evolutionary history, blastoids were a component (sometimes minor, sometimes important) of echinoderm communities dominated by crinoids.
The palaeobiogeographic history of blastoids can be viewed in three phases. Phase one consisted of the initial radiation from eastern North America in the Late Ordovician, followed by an increase in diversity and geographic range in the Silurian and Devonian and culminating in a Late Devonian extinction. Phase two began with a Tournaisian (Lower Carboniferous) radiation, primarily in North America and Europe and ended in the sudden decline in blastoid diversity and abundance in the Upper Carboniferous. In phase three the biogeographic centre of the blastoids shifted eastward as the re-radiation of Upper Palaeozoic blastoids was concentrated in the Tethyan seaway not in North America and Europe. Upper Carboniferous-Permian blastoids were widespread but the most diversed faunas are found in southeast Asia and Australia.
