Body size does not predict species richness among the metazoan phyla

We present a comparative study of the relationship between body size and described taxonomic diversity in the Metazoa. We find no pattern between body size and taxonomic diversity; neither the smallest organisms nor organisms at an intermediate body size are consistently more diverse than their closest relatives. This conclusion holds for both nonphylogenetic analysis, in which phyla are treated as independent points, and analysis of independent contrasts using several recent hypotheses of metazoan phylogeny. These results appear surprising in the context of existing models of body size distributions. However, such models are built around the prevalence of right-skewed distributions and we find no evidence for such a distribution.