Citation: Sandvik, H. (2001) Fylogeni Grand Prix: dyrenes topp 10 [Animal top 10: what are the ten largest animal taxa? (In Norwegian with English abstract)] Fauna (Oslo), 54, 132–139.
Key words: Metazoa, largest taxon, phylogeny, Linnean category, species count, arbitrariness.
Abstract: Even though the question posed in the title seems to have a straightforward answer at first glance, it is trickier than might be expected. Not even the question of what is the single largest animal group is answerable: is it beetles, insects or arthropods? Any attempt to be consequent along this line of reasoning results inescapably in the answer: the largest animal taxon is Metazoa, i.e. the totality of all multicellular animals. This renders the original question meaningless, unless it is reformulated so as to exclude taxa that are sub- or superordinate to other taxa considered. In this case, the question boils down to an argument over nomination: which taxa should be nominated in the "competition for the largest animal group"? This question does not have any objective answer either, just as it is an entirely arbitrary decision what resolution I chose to give to different branches in a phylogenetic tree. A phylogeny is necessary for nomination in the sense that it can tell us which taxa are real (i.e., monophyletic). However, a phylogeny is not sufficient because no level in the hierarchy of life (with the possible exception of the species themselves) is comparable across taxa. Picking out those taxa that share a given Linnean category (e.g., "phyla" or "classes") does not make the matter more objective, because also categories are entirely arbitrary and, consequently, differ widely between different systems. The last method could be to nominate taxa of equal age. It is argued that none of these methods is right or wrong, they merely illustrate different aspects of the complex hierarchy of life.
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