METHODS OF MICROVERTEBRATE SAMPLING AND THEIR INFLUENCE ON PALEOECOLOGICAL INTERPRETAIONS: PRELIMINARY RESULTS OF A STANDARDIZED EXPERIMENT

Microvertebrate assemblages have been traditionally used for paleoecological interpretation and reconstructions of ancient terrestrial ecosystems. However, inherent biases exist in these assemblages as the result of various associated depositional and taphonomic processes. A potentially more significant bias is introduced by non-standardized collection and recovery methods of displaced fossils. This study experimentally investigates two microvertebrate localities from different facies that were sampled and analyzed using two commonly employed microvertebrate collection methods: a qualitative method (surface collection) and a quantitative method (quarrying). The results of this experiment address how fossil characteristics such as relative density, shape, size, and degree of weathering and abrasion vary within these two methods of microvertebrate collection from two lithologically distinct microsites from the Upper Cretaceous (Maastrichtian) Hell Creek Formation of southeastern Montana, USA. The goals of this study are (1) to statistically assess taphonomic differences under different sedimentary conditions, and (2) to determine how taphonomic characteristics of microvertebrate assemblages vary by collection method. The variations in data obtained from the two methods are analyzed using Chi-Square Test of Independence and Fisher's Exact Test with a significance level of p = 0.05. Both collection methods are shown to be valid approaches, but each suffers from a definable systematic bias. The results corroborate previous correlations between fossil characteristics (shape, size, and degree of weathering and abrasion) and depositional environment. Furthermore, they illustrate the importance of standardized collecting and analytical methods used in a paleoenvironmental study. The experimental design employed should be guided by clearly defined project objectives and guiding hypotheses, as well as by practical and logistical constraints.