The paleontologic reasoning that led to the recognition of time-averaged assemblages in the early 1970s, and to elaborations of the concept in the 1980s and 1990s, has now undergone considerable actualistic testing, primarily using marine mollusks. Although many more actualistic studies are needed to document environmental and taxonomic variation, the results so far greatly increase our confidence in the indirect sedimentologic, stratigraphic, and paleontologic evidence used to evaluate assemblages in the older fossil record. The strategy outlined for evaluating fossil assemblages stresses breadth of evidence, most particularly geological context and origins of the host interval.
Numerous questions remain.
We have testable hypotheses and even preliminary evidence for these larger scale patterns, and they are exciting avenues for future research. Rogers, R.R., and S.M. Kidwell Abstract. A field test across fluvial, paralic, and shallow marine facies in the Campanian Two Medicine and Judith River formations of Montana indicates that the distribution of vertebrate skeletal concentrations is poorly correlated with the inferred durations of erosional and omissional hiatuses. Instead, vertebrate concentrations associated with discontinuities of all durations tend to be patchy, and closely track the abundance of fossil material in underlying and lateral facies. Despite being unfossiliferous itself, this discontinuity does mark a regional change in the richness of the vertebrate fossil record, with overlying beds characterized by a much greater abundance of skeletal material.