COMPARISON OF QUALITATIVE AND QUANTITATIVE COLLECTING METHODS AT THE IN SITU CASTLE ROCK RAINFOREST SITE, COLORADO

An early Paleocene (63.8 ± 0.3 Ma) fossil assemblage known as the Castle Rock Rainforest flora, located in Castle Rock, Colorado, has been extensively excavated using two different quarrying techniques. To date, over 6000 fossil plants have been recovered and analyzed and over 150 morphotypes have been identified from this in situ forest assemblage. Because the leaves were buried in close proximity to where they fell, both qualitative (“cherry-picked”) and quantitative (“census”) collecting techniques were employed to adequately represent the ancient forest floor leaf litter. Initially, we collected samples from five distinct quarries by cherry-picking, meaning that only complete or unusual specimens were collected. Interesting patterns of spatial heterogeneity emerged as a result of our initial collections. These observations prompted the development of a sampling plan to census seven discrete quarries that were ~2 square meters in area and spaced 20m apart. In these seven quarries, rigorous census techniques were employed so that every identifiable leaf fragment was collected until either 500 or 1000 specimens were tallied from each quarry. After census quarrying was completed, intact leaf layers located between the seven discrete quarries were cherry-picked, allowing for the collection of complete or nearly complete specimens. These fossils significantly supported the identification of fragmentary material gathered from the censused quarries. Specimens from both types of quarrying were scored for leaf margin, leaf area and insect damage. The census data was used to produce rarefaction curves, estimate paleoclimatic parameters and study spatial heterogeneity patterns which in turn were compared to datasets from modern leaf litter collected from temperate forest and tropical rainforests. Results from this study indicate that both quantitative and qualitative fossil-collecting techniques are needed to reflect the true nature of a diverse, in situ, fossil floral assemblage.