Don't toss out the "Wastebasket" genera!

In the most recent issue of Paleobiology Roy E. Plotnick and Peter J. Wagner investigate the nature of common fossils that dominate most collections. By exploring the online database "The Paleobiology Database" they concluded that many genera of fossils are rare (15-25%) occurring only once in the database, while the 100 most common genera contribute to over 50% of the occurrences.

Is this an underlying biological reality or are there fundamental problems with how data from the fossil record is collected and compiled?

One of problems is that many fossil groups have not been systematically studied or revised in many years, leading to a large number of specimens being assigned to a particular genus with little regard to the validness of such assignment. These genera are often referred to as a "wastebasket" group (a term that I have seen in the literature as fall back at 1915). Plotnick & Wagner offer a nice definition of the term "wastebasket" and explain how such groupings may come about over time. Of course it is very difficult to conclude that a particular group is a "wastebasket" or not. By looking at the number of species within the group, plotted against the number of occurrences there is an almost linear relationship between the two. This implies that a problem might exist, and that when it comes to determining diversity in the fossil record one must be careful to examine the wastebasket carefully.

Plotnick, Roy E. and Wagner, Peter J. 2006. Round up the usual suspects: common genera in the fossil record and the nature of wastebasket taxa. Paleobiology, 32(1), 2006, pp. 126–146