Clinal variation, episodic evolution, and possible parapatric speciation: the trilobite Flexicalymene senaria along an Ordovician depth gradient

Publisher Website
Google Scholar
Abstract
Pygidial segmentation in the trilobite F. senaria changes with time (as measured in relation to bentonite beds) and with depth (as measured along downslope transects along bentonite 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 [USA]. The pattern of strictly temporal change resembles a punctuation between equilibria. This evolutionary episode, a 106 yr interval of continuous change, may represent parapatric speciation. The clinical 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.