Paleontological Census and Unclear Taxa
Richard Javier Stephenson
The main concern of this paper is whether the use of phylogenetic species concepts in paleontology affect the choice to use higher-level taxonomic ranks in biodiversity analysis. It seeks to address this question and see if there may be a solution to the conflict of undefined higher ranks but often inaccessible species, namely in the devaluing of species as a natural concept of interest in paleontological phylogeny.
An interesting area of conflict in systematics can be found in the difference
between how paleontology and neontology count taxa and what for. The counting of groups of organisms is often used to understand trends in evolution, speciation, extinction, the composition of ecosystems and understanding the general diversity of life on Earth. In neontology diversity is most often counted via genes, species or ecosystems. (Liu, Zhang, and Hong 2011) However, in the case of paleontology there is less clarity in what should be counted and how. For more recent biodiversity events, such as the end-Pleistocene extinction of large terrestrial mammals, there is enough confidence in known species that these can at times be compared with modern groups. (Turvey and Fritz 2011) However, as highlighted by Raup & Sepkowski (1982), the uncertainty of the fossil species record has resulted in biodiversity counts favoring the use of higher taxa, such as genera, families or orders in the investigation of major events through the Phanerozoic.
This use of higher ranks presents two issues for paleontologists. The first is that the lack of confidence in species for taxa counts means that such counts do not use the only naturally defined taxon rank. The second is that the use of undefined higher taxon ranks means that there may be inferences being made in the biological record that are based on units which have no definitions or reasonable basis for comparison. What, then, would motivate the use of such taxa in the formation of hypothesis about historical biodiversity? Additionally, are there potential solutions to this conflict, such as a how to conceptualize species or to consider the lack of definitions of higher ranks?
This paper considers two potential solutions to this problem. The firs tis to consider what the use of genus as a possible substitute for species in paleontology and what its use might imply of other ranks and assumptions made in paleontological research. The other is a consideration of what a phylogenetic species concept in paleontology implies for any major grouping in paleontology, be it a ranked taxon or a defined clade and their use in taxon-counting.