PROJECT SUMMARY

COLLABORATIVE RESEARCH WITH WILLIAM AUSICH OF OHIO STATE UNIVERSITY: Evolutionary Success in Marine Invertebrates: Testing the Relationships between Eurytopy, Longevity, and Geographic Range in Carboniferous Crinoids

            Both environmental and biogeographic factors contribute to evolutionary success, which is achieved in many ways, including taxonomic longevity and diversity.  Previous studies indicate a positive correlation between taxonomic longevity and breadth of environmental adaptation, or eurytopy, in a variety of organisms.  The ability to live in a wide range of environments apparently affords taxa greater extinction resistance.  Additionally, there is some evidence supporting a positive correlation between longevity and geographic range.  Greater geographic range may reflect either greater eurytopy and a corresponding ability to colonize new areas or simply that greater longevity affords taxa more time to colonize new areas.  Current understanding of reasons for evolutionary success is incomplete, and thus, it is important to test further the relationships among eurytopy, longevity, and geographic range to determine if these relationships are valid general processes that can help explain patterns of evolutionary success and failure.  Data supporting these ideas are limited for Paleozoic marine invertebrates.  Thus, analysis of a group such as late Paleozoic crinoids will substantially broaden our understanding of the relationships among eurytopy, longevity, and geographic range.

            Crinoids were among the most abundant marine animals of the Paleozoic, and Lower Carboniferous rocks record the peak of crinoid generic diversity within the Phanerozoic.  The P.I.s' understanding of crinoid taxonomy and paleoecology permits testing the relationships among eurytopy, longevity, and geographic range both within and between various clades.  We propose to do this by comparing the mean stratigraphic and geographic ranges of genera within crinoid clades between North America and Europe, the two regions with the best fossil record.  The study will include the Kinderhookian to early Meramecian epochs of the Mississippian Period (Lower Carboniferous) of North America and the equivalent Tournaisian to middle Visean epochs of the Lower Carboniferous of western Europe (354-335 Ma).  The correct stratigraphic and geographic ranges of genera will be determined by reviewing all known species for correct generic assignment.  This will produce a true picture of endemic vs. cosmopolitan genera.  Currently there appears to be much false endemism because of uneven taxonomic treatment between North American and European crinoids, which obscures true evolutionary patterns.  Simultaneously, data on environmental distribution will be tabulated for genera on both continents to calculate a eurytopy index value for each genus, both intracontinental and intercontinental.  Stratigraphic and geographic ranges will be determined by review of the paleontologic literature and study of major world museum collections.  Stratigraphic range will be converted to longevity using accepted radiometric dates for the rocks of the study interval.  Eurytopy will be determined from review of published sedimentologic studies of the crinoidal rocks and direct observation of sedimentary facies at known fossiliferous outcrops in both North America and Europe.

            Successful completion of this investigation will bear directly on evolutionary theory as it endeavors to explain the history of life on Earth.  The derived, extensive data set will help elucidate the roles of environment and geography in determining generic longevity and, ultimately, clade longevity in defining evolutionary success.