Abstract

With the exception of the Neogene, it is difficult in much of the fossil record to measure range offset; that is, the difference in age between the first or last occurrence of a species in a local section and its time of origination or extinction within the sedimentary basin. A coupled simulation that incorporates a model of sedimentary basin fill, a random-branching model of evolution, and a model of the ecological characteristics of species is used here to explore stratigraphic and ecologic controls on range offset. Median values of range offset in much of the fossil record are predicted to range from several hundred k.y. to a few m.y., for a wide variety of stratigraphic architectures and species ecologies. Higher than average values of range offset are favored by unconformities of long duration, rapid facies changes of large magnitude, persistent monotonic trends in facies change, increased facies specificity of species, and decreased species abundance. These model predictions can be used as a guide for interpreting field data on first and last occurrences, such as evaluating zones of likely high or low biostratigraphic precision. Similarly, these results can be used to evaluate the support for paleobiological interpretations of local radiations, migrations, and extinction episodes.

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