The fossil record is adequate to determine the general patterns of diversity of genera and higher taxa across geological time, for most groups of organisms. The Linnaean hierarchy, in which most of the fossil groups have been classified, is ideally suited for such studies. Marine invertebrates are represented by three successive faunas that display increased diversities, but lower evolutionary turnovers; perhaps increasing specializations favoured lineages with higher extinction resistance. Tetrapods are also represented by three faunas that display increasing diversities and similar though more complex patterns of decreasing evolutionary turnovers. Tracheophytes have been placed in four Phanerozoic floras with generally increasing diversities, but by contrast with animals display increased species turnover with increasing diversity, perhaps in response to competitive requirements imposed by the successive origination of major clades.
The Linnaean Hierarchy and ‘Extensional Thinking’