COMPARATIVE TAPHONOMY OF THE MAMMALIAN REMAINS FROM THE CABBAGE PATCH BEDS OF WESTERN MONTANA (RENOVA FORMATION, ARIKAREEAN): CONTRASTING DEPOSITIONAL ENVIRONMENTS AND SPECIMEN PRESERVATION

摘要

The study of faunal change through time in the fossil record requires a careful assessment of the potential biases introduced by the filtering of death assemblages by depositional environments and other agents of accumulation such as predators. The investigation of taphonomy of the mammalian remains from the Arikareean-aged Cabbage Patch beds of western Montana reported here used both sedimentological evidence and characteristics of the preservation of the fossil specimens to test two hypotheses regarding their preservation pattern: (1) the pattern of faunal change through the section is not a product of differences in the preservation of fossils and (2) the taphonomic characteristics of fossil specimens are linked to the environments in which they were preserved. The interpretation of the sedimentological data, combined with the analyses of the taphonomic filtering of mammalian fossils, suggests that the attritional accumulation of fossils in floodplain settings was the result of predator activity, attrition, and local reworking by fluvial processes. The fossils from these deposits experienced little transport. Moreover, despite complexities in the dataset, select specimen characteristics, including size, shape, and surface modifications, can be linked to the depositional environments determined from sedimentological data. The fossils recovered from a high energy deposit of the lower Cabbage Patch are significantly different from those found in low energy deposits. These low depositional energy fossil assemblages appear to be sufficiently taphonomically similar to be used in faunal analyses despite a change in postmortem filtering through the section.