Diversity and disparity are decoupled in the most ecomorphologically diverse rodent radiation

One of the major questions of evolutionary biology is what mechanisms drive the outstanding species diversity and morphological disparity across the Tree of Life. Using a species-rich and ecomorphologically diverse lineage of rodents, Hystricomorpha, we (i) estimated lineage diversification and morphological evolutionary rates from measurements on more than two thousand specimens, and (ii) tested for an association between those rates. We found support for an overall decoupled dynamic between diversification and morphological rates, with these quantities generally uncorrelated through time. However, our results highlight a major positive shift early in the evolution of the subterranean family Ctenomyidae, characterized by coupled lineage and phenotypic diversification. In addition, we find a decoupling of skull shape and body size evolutionary rates, suggesting that using any single morphological metric may obscure the evolutionary trajectory of a clade. Hence, by uncovering the complex macroevolutionary dynamics of Hystricomorpha, we present evidence in favor of multiple biogeographically and ecologically mediated modes of evolutionary change rather than a single adaptive radiation style of evolution. The extensive fossil record of Hystricomorpha will permit future investigations of ecomorphological diversification within this unique clade.