INFLUENCE OF COLLECTION METHODS ON ASSESSMENTS OF PALEOCOMMUNITY ECOLOGY: A CASE STUDY FROM THE EARLY MIOCENE OF WYOMING

Numerous recent studies in vertebrate paleontology have focused on reconstructing the ecology of terrestrial fossil communities. Large collections of specimens from stratigraphically well-resolved sites are often used to study change in community structure through time. One of the biggest impediments to such studies is that taphonomy alters the composition of fossil assemblages relative to the faunas from which they are derived. While most taphonomic biases can only be recognized, and not removed, collecting procedure is a preventable source of taphonomic bias. Collection bias can significantly alter the composition of a collected assemblage relative to the one present in the rocks. This study endeavors to determine how large an influence collection method has on analyses of community structure. The data set used to address this question is a sample of roughly 4800 vertebrate specimens from the early Miocene Split Rock local fauna, which was collected both by surface picking and screenwashing. Results indicate that the species richness values derived from the two different methods are fairly similar; however, the structure of the reconstructed community is dramatically changed by the method of collection. Also, the relative proportions of specimens collected by the different methods has a strong influence on the reconstructed community structure, although species richness is again not strongly influenced by this factor. When change through time in community structure is considered, these problems are magnified by changes in proportions of specimens collected by different methods. It is clear that changes in the mode of collection can have large effects on our assessment of how ecology has changed though time. Accounting for collection methods will make it possible to get a clearer picture of paleocommunity ecology.