Effects of Different Data Types on Paleocommunity Analyses: A Case-Study from the Finis Shale (Pennsylvanian) of Texas

Most paleoecological studies apply multiple analytical techniques to one data type (e.g., abundance, biovolume, biomass); few have examined multiple data types using one analytical tool. Here, we use a consistent protocol to compare and quantify the different ecological signals determined from 1) the use of biomass versus abundance data, 2) inclusion or exclusion of taxa that are colonial or frequently disarticulate post-mortem, and 3) various taxonomic levels (i.e., generic, clade). The Pennsylvanian Finis Shale of Jacksboro, Texas is an ideal sampling locality to collect diverse, abundant, and well-preserved assemblages. We examined the >2.8 millimeter size fraction from nine 13 liter samples collected from a 2.7-meter thick section. The total biomass of specimens was 590.2 grams from 53 genera in 21 clades. Abundance counts, which could not include colonial organisms and taxa with extremely high disarticulation rates, totaled 2956 specimens among 36 genera in 18 clades.

Using Relative Sorensen distances, we performed Bray-Curtis (Polar) ordinations on different combinations of data-types (i.e., abundance or biomass, of genus or clade, for all genera or only brachiopods) to infer ecological gradients among taxa (R-mode) and among samples (Q-mode). Pearson's and Spearman's rank correlations between the Q-mode first axis scores, which account for 79%-91% of the variation in the data, yielded significant results (p<0.05) among the following: abundance and biomass, all taxa and brachiopods only, genus and clade.

These data suggest that within the larger size-fraction, certain brachiopods within each clade are driving the community structure at this particular locality. The above correlations and the strong separation between A) benthic molluscs+Crurithyris+Neochonetes, and B) other brachiopod taxa in R-mode ordinations support the primary role of brachiopods and molluscs in structuring benthic communities. However, these results are provisional, as the yet unstudied small size fraction (<2.8 mm) includes abundant fragments of the non-brachiopod and mollusc fauna.