Clinal variation, episodic evolution, and possible parapatric speciation: the trilobite Flexicalymene senaria along an Ordovician depth gradient |
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| Authors: | JOHN L. CISNE GEORGE O. CHANDLEE BRUCE D. RABE JILL A. COHEN |
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| Affiliation: | Department of Geological Sciences and Division of Biological Sciences, Cornell University, Ithaca, N.Y. 14853, U.S.A.;Department of Geological Sciences, Cornell University, Ithaca, N.Y. 14853, U.S.A.;Keymark Systems, Lake Zurich, III. 60047, U.S.A.;Department of Microbiology, Cornell University, Ithaca, N.Y. 14853, U.S.A. |
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| Abstract: | Pygidial segmentation in the trilobite Flexicalymene senaria changes with time (as measured in relation to bentonite beds) and with depth (as measured along downslopc transects along bentomtc beds and as measured by gradient analysis of fossil assemblages) along a 'fossil' depth gradient in the Middle Ordovician Trenton Group in central New York State. The pattern of strictly temporal change resembles a 'punctuation' between 'equilibria'. This evolutionary episode, a 106 year interval of continuous change, may represent parapatric speciation. The clinal gradient is strongest during this episode and is weak or not apparent outside it. Strictly temporal change takes place by way of temporal change in the cline's shape. □ Evolution, geographic variation and dines, gradient analysis. Middle Ordovician, morphometry, speciation, Trilobita. |
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