PULL OF THE RECENT? WHAT PULL OF THE RECENT? AN ANALYSIS OF MARINE BIVALVES

Geologic range data on Cenozoic marine invertebrates indicates a marked increase in generic diversity through the Cenozoic and especially the Neogene. This increase may be partly an artifact if the Recent fauna is sampled more completely than the fossil fauna. That is, recorded fossil diversities in the late Cenozoic would be lower if ranges were not extended by Recent occurrences. Raup termed this effect the Pull of the Recent. To assess the magnitude of this effect in marine Bivalvia, we compiled Pliocene and Pleistocene occurrences for all living genera and subgenera in the fossil record to determine the proportion of taxa whose fossil ranges are extended by Recent occurrences. We revised Sepkoski’s compendium of 841 living genera with fossil records, eliminating 15 synonyms and adding 118 genera, many through taxonomic revision of older literature, for a total of 939 living genera. Of these, 866 (92%) occur in the Pliocene or Pleistocene. Thus, inflation of Cenozoic bivalve diversity due to range extensions can be no more than 8%, and, contrary to previous suggestions, has little impact on the trend of Cenozoic diversity. The missing genera are chiefly endemic to regions where Pliocene and Pleistocene faunas are not well-studied (e.g. Indian Ocean, West Africa) so further work should decrease their numbers; we found little effect of shell mineralogy or body size. Bivalves are one of the "core taxa" of post-Paleozoic faunas, and so are probably a good proxy for the general invertebrate record, and reflect broadly the diversity trends of the Cenozoic biota. Although other factors relating to fossil preservation might increase Neogene diversity relative to earlier times, the Pull of the Recent is at most a very slight tug.