Abstract
Comparisons of paleofaunas from different facies are often hampered by the uncertainty in the variation of taphonomic processes biasing the paleoecological parameters of interest. By examining the taphonomic patterns exhibited by different facies in the same stratigraphic interval and area, it is possible to quantify this variation, and assess inter-facies comparability. The fossil assemblages preserved in Badlands National Park (BNP), South Dakota, have long been a rich source for mammalian faunas of the White River Group. To investigate the influence of the variation of taphonomic bias with lithology whilst controlling for the influence of changes in patterns of taphonomic modification with time, taphonomic and paleoecological data were collected from four mammal-dominated fossil assemblages (two siltstone hosted and two sandstone hosted) from a narrow stratigraphic interval within the Oligocene Poleslide Member of the Brule Formation, in the Palmer Creek Unit of BNP. Previous work in the region confirmed that the two major lithologies represent primarily aeolian- and primarily fluvial-dominated depositional environments, respectively. A suite of quantifiable taphonomic and ecological variables was recorded for each of the more than 800 vertebrate specimens studied here (857 specimens were studied in the field, 9 specimens were collected and are reposited at BNP). Distinctly different patterns of taphonomic biasing were observed between the aeolian and fluvial samples, albeit with some variability between all four sites. Fluvial samples were more heavily weathered and abraded, but also contained fewer large taxa and fewer tooth-bearing elements. No quantifiable paleofaunal differences in generic richness or evenness were observed between the respective facies. This suggests that while large vertebrate taxonomic composition in the region did vary with paleodepositional environment, there is no evidence of confounding variation in faunal structure, and therefore differences between the assemblages are attributed to differing preservational environments producing a taphonomic overprint on the assemblages. The lack of apparent taphonomic bias on paleofaunal structure suggests that such paleoecological data can be compared throughout the Poleslide Member, irrespective of lithology.
Highlights
Taphonomic biasing is one of the major obstacles impeding paleoecological reconstruction
Of the four potential outcomes of the taphonomic and palaeoecological comparisons of the Poleslide Member assemblages (Table 2), our analyses demonstrate that, while the patterns of taphonomic modification exhibited by assemblages from different facies differ significantly, both diversity and taxon abundance structure are indistinguishable between facies
We suggest that the Palmer Creek faunas are preserving some aspects of the Oligocene paleofaunal structure of the Poleslide Member
Summary
Taphonomic biasing is one of the major obstacles impeding paleoecological reconstruction. In this study we assess both the taphonomic biasing and the faunal structure of assemblages from two distinct depositional environments within the same formation to better understand how preservational environment influences paleoecological signal fidelity. Initial study of the WRG in the area of Badlands National Park drew on outcrops from all areas administered by both the National Park Service and the Oglala Sioux Tribe, and noted some significant differences in lithology and fossil composition within formations and members of the WRG in different regions of the park [13]. Courtesy of the collaboration of the Oglala Sioux Tribe and the Oglala Sioux Parks and Recreation Department, we were able to undertake the first significant paleontological survey of an area of the South Unit in more than 30 years, focusing on sections within the Palmer Creek Unit (Fig 1)
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