Biovolume Revisited: A Relative Diversity Index for Paleological Analyses

A new application of the biovolume abundance index is proposed for relative diversity demography in paleoecological analyses. Use of this technique will improve confidence in data validity and solve the following inadequacies of other numerical census techniques: all groups are treated equally, samples from different lithologies can be meaningfully compared, colonial and solitary organisms are treated equally, whole and fragmentary fossils are treated equally, and time averaging effects are assumed. Biovolume is the paleontological analog of biomass, and it is a measure of the relative amount of energy expended by organisms to secrete skeletal material that has been incorporated into the rock record. OHIOJ . SCI. 81(6): 268, 1981 During the past 15 yr, statistical treatment of paleoecological data has become quite fashionable. Cluster analysis (Valentine and Peddicord 1967, Hohn 1976), factor analysis (McGhee 1976), and canonical variate analysis (Buzas 1972) are a few techniques that have provided insight to paleoecological studies. In evaluating such studies, concerns for data base validity can be raised. Was sampling and sample evaluation completed in a statistically random manner, were all groups treated with equal rigor, and how comparable are samples from different lithologies? In analyses that utilize relative abundance data, additional problems arise. How were colonial organisms counted, how were fragmentary organisms counted, and what effect does time averaging and variable life spans among different species have? These and other problems may prejudice paleoecological data. The reliability of any paleoecological study is a function first of the fidelity of the primary data collection and only secondly of factors such as the mechanical manipulation and interpretation of quantitative techniques. The paper will outline a new means by which to use the biovolume relative diversity index introduced by Walker (1972a, Manuscript received 2 June 1980 and in revised form 27 January 1981 (#80-30). 1972b). Many of the problems mentioned above can be overcome with this biovolume method, thereby increasing the confidence in the data base. In order to bring attention to the biovolume index, I will only discuss this procedure here. The paleoecological interpretation of the faunal data used is presented elsewhere (Ausich 1979). Initial reconnaissance of fossiliferous localities during a paleoecological study of Lower Mississippian (Edwardsville Formation) delta platform sediments indicated that crinoid stem debris and broken bryozoan colonies were numerically the most abundant faunal elements. Standard methodology entails counting the minimum number of individuals of each species in a given sample and excludes consideration of fragmentary faunal elements. This methodology was considered inadeqauate for this Mississippian study, and it is probably inadequate for many Paleozoic settings. In previous studies, taxa such as crinoid pluricolumnals, bryozoans, and algae were normally treated separately from other groups and were classified as being either abundant, common, or rare. Meaningful comparison between abundant-commonrare determinations and numerical counts of different taxa from the same sample cannot be made. Only in extremely rare instances where crinoids and bryozoans are