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Table 1. Compilation of biostratigraphic zones for the Frio and Anahuac Formations from the literature. Although biostratigraphic markers are generally listed in stratigraphic order, there are differences in interpretations found in the geologic literature and differences based on geographic area. In this table, the Anahuac Formation is placed in the upper Oligocene, based on Galloway et al. (1991). Key: * denotes occurrence in Chickasawhay Formation; ** denotes occurrence in Paynes Hammock Formation.