TESTING SPECIES-ABUNDANCE MODELS OF THE HUGHES CREEK SHALE (CARBONIFEROUS) OF SOUTHEASTERN NEBRASKA

The Hughes Creek Shale Member of the Foraker Formation (Carboniferous) is exposed in road and stream cuts in Richardson County of southeastern Nebraska. Two coeval exposures separated by approximately 16 km were sampled extensively for (mostly) invertebrate fossil specimens, yielding over 5,000 individual specimens. Brachiopods dominate, but Bryozoans, Echinoderms, Molluscs , Cnidarians Arthropods and Chordates are also represented among the 36 species recovered. All taxa were identified to the lowest taxonomic level possible, then counted using (mostly) MNI (minimum number of individuals) methods. Counts of the fauna were then compared with the geometric, log-series and log-normal species abundance models. For a null hypotheses of no difference between actual data and the models, goodness of fit tests of all samples for both exposures were not significant for the geometric and log series models, but highly significant (P< 0.005)for the log-normal model. The log-normal model of species abundance fits many large, mature communities today, and that assumption is extended to the Hughes Creek Shale fauna. At both exposures, maximal faunal diversity occurs less than one meter above presumably anoxic, black shales, suggesting that reassembly of these mature paleocommunities occurred quickly once oxic conditions returned.