On the temporal inconsistencies of Linnean taxonomic ranks

The inconsistency problem in systematics refers in part to the fact that disparate taxa of identical Linnean rank are not necessarily similar or even readily comparable in any other specifiable biological feature. This shortcoming led to a 'temporal banding' proposal in which extant clades associated with particular taxonomic ranks would be standardized according to a universal metric: the absolute time of evolutionary origin. However, one underexplored possibility is that same-level taxa in disparate organismal groups already might be similar (fortuitously so) in evolutionary age. In the present study, we explicitly address this possibility by reviewing published molecular inferences about the known or suspected origination dates of taxonomic genera, families, and orders in diverse organismal groups. Our findings empirically confirm that currently recognized taxa are far from temporally standardized, thereby adding support for the contention that this kind of taxonomic inconsistency should ultimately be rectified in our biological classifications. © 2011 The Linnean Society of London